solarbird: (Lecturing)

All those posts I made about data cleanup and old hard drive data recovery got someone I know from my old SF club interested in his old Amiga hard drives, which he sent me, and which I imaged for him, and did as much file recovery as I could.

One of them was just fine – complete image, files pulled off separately as well, life is good. The other…

This is what’s actually in the disk’s partition table.

And for those who have no idea what that means: disks can be divided up into smaller disks, more or less. There are reasons to do this, mostly on servers, mostly not workstations, but whatever. These are called partitions.

This particular drive is cut up into six, count ’em, six partitions, sort of, except that two are completely broken and one is made up of parts that are also at the same time parts of two other partitions, and just kind of… overlayed atop each other.

Spoiler: this don’t work.

It’s like if you got to chapter two of a book, and midway through, chapter three appeared, overprinted and interleaved with the second half of chapter two. And after chapter two ended, chapter four picked up, printed underneath the rest of chapter three, making chapter four unreadable. But you can still make out chapter three if you squint.

There is no partition utility in the world which would let you do this.

The amazing thing is that I managed to recover the contents of both “TWork” partitions, which is a lot like getting chapters two and three from my analogy back and sorted out separately and readable. Couldn’t do anything for chapter four, though. And chapter six… I don’t know what happened there. It’s some kind of goddamn chainsaw murder scene with horror movie implications.

Sadly, both of these drives did the all-too-common very-old-drives-out-of-storage thing, where I managed to image them and pull contents, but after one last heat up/cool down, they just said “aaaaand we’re done here” ’cause that seems to be that. They’ll work long enough to come online, but the Viking won’t even stay up long enough to format it, and the Quantum ST will format, but will only let you write between 10 and 60 megs before taking itself offline and hiding from the controller until you reboot the machine. So no eBay listings for these.

Still, I’m happy. I made enough auctioning off all this old stuff to buy another microphone kit and I am closing in on another toy. Expect more DIY studio gear posts! It’ll be fun. 😀

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solarbird: (korra-fruck-out)

This is what’s left of the rubber feet of my 1994 Commodore Amiga 4000/040.

Yep. That’s a viscous tar-like residue that ran along the bottom of the case and into the gap between the bottom case and the cover. It’s very sticky and resistant to detergent, but, fortunately, not to citrus-based sticky tape removers. Isn’t it gross? I mean, seriously, doesn’t this look like some sort of OOZE OF SATAN special effect?

Oddly, the stickytape used to hold the rubber feet on was intact! And, as far as I can tell, fine. This actually saved me a lot of cleanup, because the cores of the old feet were pretty solid? The further I removed down, the more like rubber it became. The thickest material had an actual rubber-like consistency.

Fortunately, all the rubber that ran could be cleaned up pretty easily with an old spudger and a lot of orange oil. But goddamn.

I’ve repaired tube equipment from the second world war and this is the most bizarre materials degradation I’ve ever encountered.

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solarbird: (molly-oooooh)

I wanted to post about the cool second-generation crystal microphone today BUT NO IT’S ALL STUPID AND NOISY AND I DON’T KNOW WHY but it sounds like either a really bad cold solder joint (please be that) or a bad transistor (@&*$&!!! special orders please don’t be that) and I don’t know which.

It’s too bad because I came up with a nice little jury-rig jig (say that five times fast) and so the backplate of the housing came out really well and I was looking forward to showing that off. Fingers crossed this is some sort of Surprise It’s Easy! fix – that would indeed be a surprise, to be honest about it, but a pleasant one.

In the meantime, enjoy this video of Overwatch players in custom game mode making some genuinely gorgeous Genji Beams. These are effects created by lining up opposing teams of Genji players opposite each other, in continuous-shot-deflection mode, and hitting them with various weapons. The shots bounce back and forth between the teams, and you get some really neat graphics interactions. It’s pretty cool and occasionally hilarious. Enjoy:

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solarbird: (made her from parts)

I’ll be at Orycon this weekend! I have panels and workshops and a concert on Sunday afternoon, so please come out for it!

They’ve actually given me a panel on building old-technology microphones, which is pretty cool, and I’ll let people record themselves on a 1920s-ish carbon mic and a 1940s-ish crystal mic, so hopefully that will be fun. People really seemed to enjoy it when I had the setup running at my dealer table at CBCC.

I need to find time – somehow – to wedge in building a new amp board for the microphone panel, because I don’t want to take apart the existing crystal microphone for show-and-tell, and I think it’ll be neat to show that off. Later today. Hopefully. Assuming nothing else explodes.

Like, Monday, right? Things Happened, and then I got to spend the afternoon pulling unimaginably gross material out of a fluid pump system while going, “oh gods, oh gods, I hope this is only cat litter, please let this just be cat litter,” and when that’s happening, you have officially reached what one might call a BAD SCENE.

Not “darkest timeline” bad scene, but: bad.

so disgusting

Anyway. Thank the gods that’s over. See you this weekend!

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solarbird: (music)

Oktava has some great microphone designs. But the quality of the components can be pretty random, particularly in the used market, since a nontrival number of those were made in the early post-Soviet era. My two 012s sounded pretty different – one in particular rather unpleasantly harsh – so I implemented Recording Magazine’s recommended component upgrade* on the harsh one, which we’ll call Nr. 1.

Nr. 1 may have been modded a bit before. It’s certainly been opened before; one of the three screws was stripped and useless, the other was jammed badly. I had to drill both out, so I’m hoping I can order replacements. The third was fine.

As soon as I had the microphone open, I saw what Recording meant by random components. The key transistor was a make so old that it had a metal shield ground cap, and separate lead to that cap, something I haven’t seen in gear made after about, I don’t even know, 1978? I also saw what they meant by “fragile circuit board,” because wow, you could lift these circuit board traces with an overly-aggressive hair dryer. Take care!


Comrade!

Still, it was mostly a matter of being methodical and not rushing things, and in good time, I had the key components upgraded, with no surprises other than the transistor’s extra lead.

These are three unmodified before/after snippets in one recording – recorded under identical conditions other than the internal microphone electronics – of Oktava mk-012/mc-012 nr. 1 in my studio. Even on laptop speakers, I can hear the harshness, particularly in the first sample. In all cases, it’s pre-modification first, then post-modification after:

Oktava MC-012 nr. 2 sounded very different to nr. 1, before; opening it, I could see that the components used were of a significantly more modern variety. It may well have been made later, which would be part of that. Now, the two microphones sound much more like each other, indicating that nr. 1 really was meaningfully different in component quality.

Here is a recorded comparison of nr. 2 (still factory) and nr. 1 (upgraded). These recordings were made simultaneously, with the two microphones right next to each other. The differences are much subtler, but I think the upgraded nr. 1 has a bit more presence – or maybe sense of stage – than the factory nr. 2. Despite being mono recordings, it’s almost like there’s a slightly better stereo image in the modified nr. 1… but give a listen and hear for yourself, see what you think.

You’ll definitely need headphones to have any chance of hearing anything interesting here. Factory nr. 2 comes first in all cases:

So, all in all, very glad I did this to nr. 1; pretty sure I’m going to go ahead and do it with nr. 2 as well, though I expect a much less dramatic change.

The only thing I’m thinking about now is – there’s a bank of capacitors in back. They’re good ones – Philips, not generic, which have a good durability and spec-compliance record. (I don’t know whether they’re original; some Oktava 012s shipped with quality caps already in place, and their track record has improved with time.) So I shouldn’t need to upgrade them – and the article at Recording Magazine says not to bother if you already have “improved” capacitors.

But I don’t know how old these are, and electrolytics have a lifespan. That’s measured both in calendar time (years), and in use – tho’ the latter is in tens of thousands of hours, and these mics are certainly nowhere near that.

The small downside is time spent, the large downside is the possibility of circuit board damage, which wow I don’t want. The upsides would be 1. possible sound improvement if they are aging already, and 2. Never having to think about it again, in practical terms.

So I dunno. Get it out of the way, or leave sleeping caps lie? Hm.
 
 


*: errata for the linked article: Capacitor “C6” in the parts list is actually capacitor C1; there is no “C6” in the build description or circuit diagramme; I assume this is a typo.

Also, some of the items in their parts list are no longer made, but they have exact replacements. R1/R2 exact replacement part number as per my October 2016 Digi-Key invoice: MOX200J-1000ME-ND. Capacitor C1 (listed as “C6” in parts list, see previous paragraph) current part number: 445-4737-ND. Capacitor C2 current part number: 399-1418-ND. Capacitors C3 and C4: 4073PHCT-ND. Capacitor C5: 4047PHCT-ND. Mostly, the substitutions are lead-free versions replacing earlier versions with lead.

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solarbird: (made her from parts)

I made a thing! It’s called a focus knob. It’s quite simple and normally you’d built it into an electric guitar as a guitar mod, but since I don’t have an electric guitar, I built it as a pluggable external box.

Basically a mild high-pass filter that serves to pull out ‘boominess’ from instruments, it puts a bit more of an edge on an instrument’s sound – the more you turn it up, the greater the change. As effects go – on my zouk, anyway – it’s pretty subtle. But it’s also the kind of shift that is multiplied by later effects added in, and changes how later-in-chain boxes like distortion pedals work.

As you can see from the instructions here, the wiring takes all of about 20 minutes’ time. But it’s good warmup for making a bunch of component upgrades to my Oktava 012s, and I already had all the parts from the Great Radio Shack Lootfest of 2014. Plus, hey, cool hard candy tin!

So I have a a HARD CANDY knob now. It goes from Hard to Candy. Yum. 😀

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solarbird: (molly-oooooh)

Several months ago, I saw online a prototype of a sampling synth with waveform editing and a uniquely cool physical user interface. I don’t remember whether I blogged about it at the time or not, but I certainly talked about it on social media and such.

It’s not so much that it does anything you can’t already do; you can do everything it’s doing with a modern digital audio workstation, for example. But the physicality of the interface looked delightful, and that sort of thing really, really matters in instruments. Including synths. It made sample synths look fun to play in a new dimension – one far more instrument-like than I’d seen before.


Collidoscpe v2

I wondered at the time if they were looking for a commercial application, to build them to sell. But if they were, they’ve ditched that: it’s gone open-source. Not just source code for the software, but instructions and 3D CAD files if you want to build one yourself to their physical specs.

Admittedly, the case-build instructions are… a tad sparse. But that’s half the fun, right? Component-wise, it’s basically a cakewalk. (Silly me thought the waveform display was some fancy custom thing HAHAHAHAHAHA NO IT’S A STANDARD LCD MONITOR BEHIND A FRAME HAHAHAHAHA etc. But that’s the smart way, so.)

Anyway, yeah! Project!

h/t: Klopfenpop for the link

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solarbird: (Lecturing)

Well, that was neat – the “warmup” storm was the big one, the big one swerved north at the last minute and weakened, mostly missing us, and then surprise-collapsing over Victoria. Still, we did lose power and were offline most of a day, so if you missed Friday’s post about recovering damaged recordings – a bit of a geek-out, really – that’s what happened.

I took advantage of the unexpected uptime to finish up that project, by the way. It was interesting, and I learned stuff, like usual. The condition of the tape (and damage in the recording) varied all over the place, and arguably too much even to try to split it up into a million shards. Though there was a lot of this kind of crap:


This is one phrase of lyrics

That’s a combined automation of level and compression ratio. Here’s what it looked like over a larger area, about 3/4 of the way through. Yes, meaningfully more got added to this:

And the sad thing is, that’s just me trying to attain listenability throughout. I’m not trying for “good” – that isn’t attainable, but less noise and less distortion and fixing dynamics over time, that I can do.

Some of the tape wasn’t really that bad! I mean, it’s a 23-year-old cassette recording made on some sort of portable device set on what sounds like two different autolevelling schemes – it changes once when the recording was stopped briefly, I suspect the operator changed modes and I really wish they hadn’t – so “not really that bad” comes with a lot of caveats. But still, not that bad. Lots of hiss, lots of tape rumble, small dropouts, and so on, but not unintelligible. Fatiguing to listen to over time.

Here’s a short sample of “The Crawl,” early on, direct from the tape. Hissy, some sort of mid-band distortion that isn’t too bad in short doses (but really gets annoying over time), off-centre sound placement. But otherwise not that bad. You can hear stuff.

So I ripped the hiss off, did some work to improve dynamics, pulled out what I could of the distortion, threw on EQ to bring back out the low end, re-centred and smoothed it a bit, and here y’are.

Then there are other sections. After that mode switch got thrown, the whole recording got weirder. “The Profiteers” was particularly bad. Here’s the original. I know the lyrics and I still can’t make them all out here. But I can in the restoration. It’s not good, but you can make things out. This is where I needed that whole stack of plugins I talked about on Friday.

And just as importantly – and something short samples like the above won’t give you – it’s listenable over time. Some of these problems are really hard to tolerate over the two hours of this recording. They’re not bad in short doses, but they grate.

Like, the original seems to have more high end, right? But it’s not real. Eventually your brain figures out it’s just hiss, with your audio centre filling shapes into it, and it’s wearying. In short comparisons, the brightness is attractive, and the restored version sounds kind of dull in contrast at first – but as with light, your ears adjust to recordings, and that goes away with listening.

Similar are all the damn-autolevel-to-hell level changes. They’re not necessarily so bad in short doses – some of those are like punches to the face, but most aren’t. But even with that, EVERYTHING REALLY LOUD PUNCTUATED BY surprise underlevelling is also wearying.

So the restoration maybe doesn’t sound good, on any kind of normal scale – but I got it to the point where, particularly on laptop speakers, it sounds pretty okay. I can listen to it. Occasionally – just occasionally – it even sounds musical. And there’s enough there there to remind me how much I miss this Great Big Sea.

There was one thing I couldn’t fix though, no matter how I tried. And that’s during “Excursion Around the Bay,” wherein early in the song, some fucker orders espresso at a George Street bar. And so you get that espresso machine foam blast noise right in the middle of a verse.

WHAT. THE. FUCK. YOU WANT COFFEE, GO TO STARBUCKS.

Gods damn you, espresso man – gods damn you.

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solarbird: (molly-oooooh)

In yesterday’s post, I posed a question: do USB chipsets matter in the 2.0 environment? I had reason to suspect they might.

The answer is holy crap yes they matter they matter so much it is unbelievable.

First, let me talk about what prompted this research, so you’ll know why this matters.

On my old sound interfaces I had live monitoring in hardware, so I didn’t have a lot of need to care about latency. Since that won’t mean much to most people, I’ll explain; when recording, it’s good if you can hear yourself, in headphones. If you’re multitracking, it’s critical.

My old audio interfaces did this with direct connections in the hardware. Whatever came in the microphones also went out the headset. There are advantages to this method, but also disadvantages, in that you aren’t actually hearing what’s being recorded, just what’s being sent in the microphone jack.

But now, I have this shiny new 1818vsl, which doesn’t do hardware monitoring under Linux. Higher-level kit generally doesn’t provide that; they’re assuming you have enough computer that your computer can send back what is actually being recorded, effects and all, and that you’ll do that instead.

This means I now have to care about latency in my system. Latency is basically delay, between mic and computer, and computer and headset. And if the computer is feeding my monitor headphones, that delay matters. You want to hear yourself live, or close to it, not with, oh, a quarter second of delay or something horrible like that.

Now, the good news was that straight out of the box on Ubuntu 16.04 (the latest long-term support version), I had better, lower latency numbers on my new 1818vsl than on my old hardware, when I was using that on 12.04. I could get down to a buffer size of 256 samples, and three frames, which gave me about 30ms basic latency – roughly half what I had with my old hardware and old install. I could use it as-was.

But I couldn’t go any lower on those buffers. One more setting down, and even playback would lag. It’d be okay until the system had to do anything else, then you’d get a playback pause, or a skip, or if recording – presumably, I didn’t bother trying – lost sound. That’s unacceptable, so 30ms was the lower limit, and I wasn’t sure it was a safe lower limit.

And that’s what got me doing all that chipset research I talked about yesterday, and I ordered a new USB card (plugs into PCI sockets) based on that research. I was hoping for a couple fewer milliseconds of latency, that I wouldn’t actually even use; I just wanted a safety margin.

So that new card arrived on Sunday, with its OHCI-compliant chipset made by NEC, and I popped it into the machine and started things up with normal settings.

At first, I was disappointed, because I only saw about half a millisecond less lag, instead of the 1-2ms drop I’d hoped to see. But across tests, it was more consistent – it was always at that same number, which meant I could rely on that 30ms latency in ways I wasn’t sure I could before.

They I decided to see what would happen moving the sample buffer setting one level lower, into what had been failure mode. And the result was 1) it actually worked just fine, where it hadn’t before, and 2) when running analysis, tests showed much lower latency at that setting than with the previous USB ports.

That was an ‘oh ho‘ moment, because it implied that the 256-sample run rate was basically the spot at which the on-motherboard USB could just keep up, and trying to run faster wouldn’t actually produce any actual processing improvement. It’d try, but fail, and time out.

So I did a couple of recordings on that, and they all worked. Then I dropped it another level, until finally, I just said hell with it, let’s just set it as far down as the software will allow and see how hilariously we explode.

I just successfully recorded test tracks four times with these settings, on the new card:

0.7 milliseconds isn’t even something you think about on USB 2.0. 2.8ms, maybe, okay. I’ve seen that managed a few times before, and that’s genuinely indistinguishable from realtime/hardware monitoring. But 0.7ms?

Seriously, this is well into “…is that actually possible?” territory. I’ve never even heard of someone running over USB 2.0 at latencies this low.

So, I guess it looks like the chipset matters a whole lot. Maybe not for most applications, and maybe not in the same way as in USB 3.0 or in FireWire, were there are serious compatibility issues. But in the 2.0 world, in realtime audio, it appears that the chipset makes all the difference in the world.

And yet, I can find this nowhere online. I’m beginning to think nobody bothered until now. Certainly when I’ve asked about it, the response has “why are you on USB get firewire” or “why are you on USB get PCI” because sure I want to throw out all this hardware and start over THANKS NO.

I think USB users have been trained just to accept it and deal. But surprise! You don’t have to! You can actually get a better USB card, if your system allows it, and it’s $30 instead of $1300!

So, HELLO, OTHER SMALL-STUDIO MUSICIANS! You want a chipset that uses OHCI on the USB 1.1 level even if it’s a USB 2.0 card or later because the 1.1 layer still matters, and still gets invoked by the higher-order drivers for card management. See previous post for why that’s important.

This means avoid Intel and VIA chipsets, and look for NEC or SiS – or anything else that loads OHCI drivers and not UHCI. If you’re on Linux, you want to:

cat /proc/interrupts | grep usb

If you see “uhci_hcd” in there, you have a UHCI chipset running your USB port and getting a new USB card with an OHCI-compatible chipset (and disabling whatever’s already installed) might help you with your latency issues.

Good luck!

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solarbird: (pingsearch)

I’ve been trying to find out whether there’s any sort of difference between USB 2.0 cards, specifically as addresses the needs of digital audio workstations on Linux.

Very few people in linux communities seem to have addressed this question at all, and none I can find on the audio side. (Firewire, oh my gods yes – huge lists. Just not USB.)

But I did a lot (a lot) of digging, and discovered via the Linux USB kernel driver dev mailing list(!) that while there’s not much difference on the USB 2.0 side, there are important differences on the 1.1 side. These difference manifest in two different driver models. That still matters at least a little bit in 2.0, because those 1.1 drivers still get loaded.

Anyway, that difference is that there are two very different driver interface models. One is UHCI, created by Intel and used by Intel and Via, mostly. The other is OHCI, which Compaq pushed when it was still around, and Microsoft preferred; it has less intellectual-property load, and NEC, SiS, and some other makers use it. If you see a “Mac compatible” card? It’s going to be OHCI.

The OHCI model puts a lot more of the business of doing USB into hardware on the card. UHCI has the processor do that work. And while that isn’t a heavy load, it is a nonzero load, and more importantly means that UHCI chipsets require more CPU attention than OHCI chipsets, on a recurring basis. And that is something we don’t need in a digital audio workstation; there are only so many board interrupt opportunities; I want them for moving data, not servicing USB mechanics.

Once I knew that, I did more searching and found people saying how switching to a NEC chipset card had (in one case in particular) ‘saved their bacon’ specifically on their digital audio workstation. They were using ProTools on Windows, not Linux, but it was still with a USB audio interface.

The chipset used by my on-motherboard USB ports is, of course, Intel, and therefore UHCI. (And UHCI drivers are actually loaded, I checked.) There’s also an on-motherboard hub between the outside world and the one true root device; that doesn’t help anything either. So there’s a nonzero chance I’ll see improvement both from changing from UHCI to OHCI, and from moving to a true root USB device instead of a hub device. It won’t be much, but I’m only looking for a few milliseconds of latency here. And even that’s more for… reliability buffer, I suppose? Yeah. Reliability buffer, rather than pure necessity.

I’m mostly posting this 1) so I remember it and 2) so other people looking for this data can find it. HI! I can’t be the only one!

I’ll update this post if I get interesting results.

eta: INTERESTING RESULTS AHOY: CHIPSETS MATTER SO MUCH OMG. I’ll write up a post with details, post it tomorrow.

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solarbird: (banzai institute)

I’ve been playing with that ‘added pressure adds bass response’ idea, for use with these piezo pickups. I made a little wooden chamber that would let me add light pressure, as with the bridge pickup design. It would be held down with a clamp for testing, but would isolate that pressure from the piezo itself.

Anyway, I made a bunch of recordings, two for control, and eight with a range of pressure in the chamber. The controls were made with the pickup taped to the front of my zouk with double-sided tape (standard attachment), and with the pickup directly clamped to the front (also a standard attachment) and come first and second in the recording. The other eight were with the pickup in the test chamber, with increasing amounts of pressure on the crystal, applied by inserting paper as seen here:


With thin cardboard and two sheets of paper

Note again that the clamp is not adding pressure to the disc in any way.

Audio samples in a single mp3, here. There is some extra noise in these recordings; I was trying the modular approach again and that’s the result. I think the TRS connectors are inherently noisy. But that’s a separate matter.

I also ran spectrographic analysis on each recording, and combined those into a single animated gif that cycles through the recordings in order. Here’s the key for both. The gif is repeating, so each frame is labelled in the upper left.

 1: taped to top
 2: clamped directly to top
 3: in chamber, no paper
 4: in chamber, thin cardboard (0.46mm)
 5: in chamber, cb+1 sheet  (+0.11mm)
 6: in chamber, cb+2 sheets (+0.21mm)
 7: in chamber, cb+3 sheets (+0.31mm)
 8: in chamber, cb+4 sheets (+0.42mm)
 9: in chamber, cb+5 sheets (+0.52mm)
10: in chamber, cb+6 sheets (+0.63mm)

You’ll note in both the graphs and the audio that bringing in the chamber at all, even with no additional crystal pressure, caused a big drop in high-end oversensitivity, and boosted the low-end. That was interesting; I have suspected for a while that the crystal side of the disc would actually be better as a source-facing element, but there are physical issues to doing that, since the wires have to attach on that side.

Adding pressure continued to boost low-end response through test 7, without inhibiting high-end response. After that, I think additional pressure began to overcome the benefits, and you see a return to a more midrange-heavy sound – though in all cases, I think it’s better than either traditional mount.

This is consistent with tests made in the bridge pickup from last week, and reminds me of a diagramme I saw of a period crystal microphone that implied the crystals themselves would be set up forward-facing.

Anyway, data! And lots of it, for lots of your crystal/piezo experimental needs.

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solarbird: (asumanga-yay)

A couple of months ago, I tried making a Cortado-based bridge pickup for the octave mandolin. It worked okay – better than the ad-hoc clamp arrangement I’d bodged together for last January’s Conflikt show, but not what I’d hoped. It was a lot more stable, but still needed lots of equalisation help.

I’ve built a new one, with a new design! It’s much better. Here’s an mp3 of the previous design alternated with the new design, on octave mandolin – no eq of any kind, no effects, just raw output from the old design vs. the new. (Old design is first.)

While working with the previous attempts, I’d figured out what really improved things was the right kind of pressure on the piezo disc itself. My thumb was pretty optimal, but you can’t exactly do that and play at the same time. The clamp wasn’t bad, but it was slippery and awkward and actually came off on me during rehearsal, so I didn’t trust it. Most piezo-style pickups live under the bridge of an instrument, but you can’t do that the usual way with this one, it’d be destroyed by the pressure.

So I went about trying to fix that.

First was to take the bridge plate and add a wide, flat channel – one wide enough specifically to contain the entirety of the Cortado piezo element. I made it by wrapping sandpaper around a flat piece of metal, and scrubbing back and forth to excavate out the wood I needed removed.


This is actually a new bridge plate.
But it’s made of the same material, so no real diff.

You need to sand away enough wood to make room for the piezo and all the tape wrappings, and some extra. But you do not need to sand away enough for the wires soldered to the disc – you want to avoid those entirely.

Keep sanding away wood until the bridge slides freely over both the new channel and the piezo, like so:

What this makes is basically a wide clamping chamber around the pickup element itself. It doesn’t do any clamping yet; it just creates a space for it. At this stage, in fact, if you hook it up and try it, there’ll no change in sound from the previous version.

(In fact, the “old design” recording I used in the sample is actually this version at this point in the process. I verified that it sounded exactly the same as the previous version, as predicted, which means I’d re-established the old baseline. Important for science!)

But now, of course, I have a clamping chamber! We just need something to apply pressure.

So what’s our clamp? Pieces of paper. Post-it notes, to be specific, just because they were handy. The right number of sheets in this exact case turned out to be four.

Five also worked, and did not feel like too much pressure inserting the papers under the bridge. But it did sound like a bit much compression, tonally, so I went back to four.

(Here’s that sample track again, alternating old design and new, old first.)

The beauty of this is that since it takes several thicknesses of paper, and since that paper be changed out without taking apart the pickup, you can use any number you like. You could even adjust the tone on the fly.

Interestingly, the pickup didn’t even get quieter with more paper. I’d worried about that, but didn’t need to. In fact, adding more sheets made it louder, meaning that the pressure is not so much “damping down treble” as it is pulling up bass. Which, in turn, makes me wonder if it’s not so much “resonating better” as moving the zero/no-vibration point of the crystals’ charge state from all-electrons-in or all-electrons out (doesn’t matter which) to a more middle-range position, which…

…hm. Actually, that’s interesting. No, that’s really interesting. That would explain why the pickup got louder with more clamping, rather than muffled or…

…huh. This is an hypothesis. If I’m right, I can make my next crystal mic substantially more modern sounding, by enclosing the piezo in a small clamping chamber, which is, like this, attached to the resonating disc of the microphone, and possibly…

…possibly I should take my SRMD meds now or I’m going to be up until 5am next Thursday playing with crystals and possibly taking over the moon again, aren’t I? Yeah. I am. Okay. BRB.

So. Yeah! I’m super-pleased with this result. I’m also thinking that maybe this could be used on other items that have flat surfaces which need pickups – like, a piano, maybe – and instead of the bridge, as here, you use a weighted flat bar of some sort across the pickup plate to create the clamping chamber. Then you’re off with tonal control via paper again. I have no need for this functionality at the moment, but it strikes me as legitimate nonetheless.

And most importantly for me, I now have a much more conventional DIY pickup for the octave mandolin. Here y’go, doc – just plug ‘er in, and we’re off.

Much better.

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solarbird: (banzai institute)

I have some mics that react badly to phantom power, so I made a phantom power blocking took. I had an old Smarties block handy, so I made it out of that.


It seemed appropriate. ^_^

I also went at improving an effects box I built a while ago called the Trash-o-Matic 68000. You would have heard it on Daleks Behaving Badly (Dalek Boy), a joke track that really needs a shorter edit, because it takes way too long to build up.

The best part of this box is the Berthold Ray effect circuit that I legit invented. That must have happened in a pretty heavy Science-Related Memetic Disorder attack (or spark hyperfocus, if you’re a Girl Genius reader), because I was trying to figure out how the hell it worked and I am here to tell you that this is some serious-business Oscillation Overthruster bullshit right here.

It’s basically a multi-store self-reducing sampler feedback effect with frequency shift that’s using the device’s amplifier as a delay loop and sending the amplified samples back to the input via a combination of the internal system ground and negative phase of a balanced signal lead. Both matter. I… don’t entirely know why.

Anyway, the whole thing is noisy as hell, and much of that is the platform I was building onto, and I was hoping to fix that. I was able to reduce noise levels somewhat – no, that’s unfair, meaningfully, it’ll be easier to gate out noise now – but it’s still buzzy as hell.

I’m kind of interested in seeing if I can re-implement the Berthold Rays in a less trashy environment. Sure, it’s fun in this mess of noise and grind and crunch, but it’d be nice to have in a cleaner box as well. Maybe I’d use it more then.

I’ve never used it for music before, but here’s a little bit of noodling I call “Broken Music Box, Found After a Fire,” played on Irish Bouzouki and run through Trash-O-Matic voice 6, with full Berthold Ray attack:

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solarbird: (banzai institute)

Okay, up front: I have built a working crystal microphone! It wants a fair amount of equalisation added to it, but that’s okay because I can do it in the digital audio workstation. (Normally there’d be some circuitry in the microphone to do that, but in this case there’s not. Reasons.) And, happily, it’s picking up the kind of range you’d expect out of one of these old mics. It may be boosting the midrange pretty hard – harder, I suspect, than traditionally – but it’s picking up a good chunk of the spectrum.

It also really should be used with a pop filter (I didn’t), because it has the biggest damn mic diaphragm you’ve ever seen:


70mm. YES 70mm I HAVE BUILT A LARGE-DIAPHRAGM CRYSTAL MICROPHONE.

So enjoy some old-school crystal microphone test recordings, made with a mic built from cardboard tubing, wires, piezo cristals, and old styrofoam cups(!), and I’ll tell you how everything I did last time got thrown out before I eventually got this to come together.

It’s 1944 Forever Faux BBC Radio: NO equalisation
Faux BBC Radio: WITH equalisation
Constant Sorrow: NO equalisation
Constant Sorrow: WITH equalisation

Okay, so, right. When last we left our intrepid crystals, I had a nice little circuit in a nice little modular box, so I could test about 90 kinds of resonating bodies without having to solder everything to everything, and maybe I could keep the most interesting ones and use them in different situations.

But it had a lot of noise – I mean, like goofy amounts – and wasn’t boosting signal the way I thought it should be. I just chalked all that up to being in a test harnesses, and all that.

WRONG.

I still don’t understand what was going on. I thought I’d built the circuit wrong, but taking a known good one and putting it into the modular box made it misbehave as well. Removing the plugs and soldering directly didn’t help either – just as much noise, just as little signal.

Eventually I figured out that if I had the circuit in the modular box, it would be full of noise and lacking amplification. But it could be the box, she said, desperately clinging to sanity, that doesn’t make sense! Besides, I’d taken the circuit out of the modular box, and set it nearby, and that didn’t help.

Then for unrelated reasons I moved the circuit further from the box. A lot further – like, up to head level.

And suddenly everything started working. NEAR THE BOX BAD. FAR FROM THE BOX GOOD. I AM NOT EVEN MAKING THIS UP. I DO NOT KNOW HOW A PLASTIC BOX LINED WITH METAL CAN DO THIS. THIS IS PUREST STUPID ACTION AT A DISTANCE AND I DON’T KNOW WHY.

Given that behaviour also improved when I shortened the cable leading to the piezo pickup, I suspect there is Something about My Cable Stock, and for now, I’m just going to leave it at that. But really, I don’t know.

That case is now Gone. It can be Someone Else’s Problem Forever.

I had also mentioned in comments a couple of places that I had a Really Cool Idea for a suspension harness to hold up the resonating element, which I’d chosen to be the base of a styrofoam cup, as it tested best overall. I was so pleased with this idea that when it utterly failed I was a whole ‘nother layer of So Very Angry.

Anwyay, the idea: take some nylon mesh, the kind used for pop filters. Stretch it across the resonating body. Adhere it to the styrofoam’s outer ring using – hm, This to That says hot glue. OKAY!

Then take that same foam and nylon assembly, and stretch the outer nylon across the microphone case’s front opening. Hold the nylon in place on the outside of the can with a rubber band. It’s perfect! The nylon is acoustically transparent, so will have no effect on sound, and being so lightweight, it won’t dampen responsiveness! It’s GENIUS!


We’ll cut away that middle mesh as soon as the glue is stable


Another can! This one make of shipping tube and aluminium tape.

ABSOLUTELY NONE OF THAT TURNED OUT TO BE TRUE! NONE OF IT!

Well, okay, it was pretty transparent in terms of frequency blocking, I guess that part was true, but even at nearly slack, the amount of response damping just… okay, when I was testing this, I was still testing it with the EVIL CASE OF EVIL, so that was probably part of it, but the amount of signal reduction just depressed me. SOUND SOUND WHAT IS SOUND NONE FOR YOU.

I don’t have any pictures of that setup, which is again because SO ANGRY. So there y’are.

After that, things started turning around. That’s about when I realised how light the styrofoam disc resonating body was. It’s made of sides of two styro cups, flattened a bit and adhesed together with very permanent double-sided tape and cut into a circle, and weighs practically nothing. It is, in fact, so light, that…

…the wire connecting it to the circuit board could maybe be used to hold it up. As long as we can hold the wire in place, that’s worth a try, right? And I’m taking everything apart anyway, so let’s try it:


Piezo crystal is on back of that foam


Circuits just kind of hanging out the back, lol


Foam pushed into the can. Giant resonating disc in front. Hit it.

And it worked. FINALLY SOMETHING ON THIS PROJECT WORKED it was such a relief – on Friday, with things just exploding everywhere, I was pretty damn crazy because seriously it was one of those escalating-personal-chaos-field days, and physics just took a holiday or something and it took a few days to hammer it back towards reality.

So then it was time to make a more proper kit. First, of course, cut some foam more precisely, so the resonator would stay held firmly in place, making sure you leave enough room for all the circuitry bits.

I used some of the leftover delrin plastic to make a back cap for the microphone can. This let me use a standard XLR connector, which I really wanted to do – wire nuts and twisting may’ve been okay in 1938, but with the amount of RF flying around the Lair (and off me!) I really can’t do that. It has to be shielded, too – more copper tape solved that problem just fine.

I still need to build a proper hanging system, so it can hang the way these are supposed to. It’s not as cool looking as the carbon microphone, I’ll just acknowledge that up front. But it’s nice and compact – relatively speaking – and it works.

Another variant will be to replace the styro with that clear Boeing plastic. When I was running tests, the signal level on that was… not real high. But neither was the signal level for anything else, and in the breakthrough moment when I figured out that somehow the plastic case was A Problem, I was using the clear Boeing resonator. And of all the things I tested, that had the best sound. So I think that’s worth another go, and I do have a spare circuit.

(I think. I think I have a spare circuit. I also have more and larger pictures, like usual, over here on Flickr.)

But even if that works, and if I prefer it, I’ll keep this one. It does have a very old-time-radio sound – newer than the carbon mic, but still… old-time.

Plus, the damn thing functions. After this past weekend, that counts for a lot.
 
 


This is part of a collection of posts on building microphones and microphone-related kit, such as mic pre-amps.

Mirrored from Crime and the Blog of Evil. Come check out our music at:
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solarbird: (korra-fruck-out)

A really weird thing is happening with the crystal mic. I do NOT understand this.

The same circuit board taken from another box and put in this box is much noisier. Like, 15-20db noiser. Both boxes are metal or metal-lined, and I’ve checked – repeatedly -the metal lining on this one is grounding.

This is true even with no crystal element attached.

Also, any board put in this box is quieter – less signal. This makes even less sense.

I’m so confused.
 
 


This is part of a collection of posts on building microphones and microphone-related kit, such as mic pre-amps.

Mirrored from Crime and the Blog of Evil. Come check out our music at:
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solarbird: (Lecturing)

Apparently, I’m really into old-fashioned microphone technologies at the moment, and really, I’m just fine with that. I’ve had this boundary-microphone idea in my head for a while – I even ordered a bunch of parts to build it – and that idea and crystal microphone technologies go together!

Okay, first, crystal microphones were an actual thing. Popular from the mid-1930s through the early 1950s, they were used on-air and in music recording. They’re still in use in certain applications, much like carbon microphones are, but more widely – if you’ve heard of a “piezo buzzer” or “piezo instrument pickup”, that’s exactly the same technology, only applied to a different goal.

The underlying physics: there are crystals which, when flexed, will produce electricity. The charge is positive or negative, depending upon how the flexing is done. Sound waves are enough to do it, which means bing! Microphone technology! This is Neat. And, yes, I have a sample mp3 below.


Hey, that 60s and 70s Skiffy fascination with crystals had to come from somewhere.
(Speak clearly into the pinky ring, Zed.)

It works the other direction, too – current one way will flex the crystal one way, current the other way will flex it back. You can make speakers out of this, and that’s been done. This is also how piezo buzzers work – cycling AC power through a piezo-effect crystal.

I’ve built a couple of piezo-based pickups before, using the Cortado kits, so that seemed like a good place to start. I’m not bothering with a second board-construction write-up; the first one is here, if you’re curious.

But building the carbon microphone driver circuit as an external box made me realise that I should build this mic using an external driver circuit as well, so I can experiment without taking apart the box every time. So I used the housing from a dead laptop power supply I’d recycled a while ago.

The best part was that the AC mains connector slot was almost exactly the right size to hold the XLR connector. I just had to file away a bit at the narrowest points. And, of course, I had to line the whole thing in conductive metal tape, for RF shielding, and ground it.


The Now-Modular Cortado. Piezo lead on the right, XLR to board on the left.


Looks almost professional!


TRS: Tip is outer disc, ring is crystal disc, sleeve is shield ground


Standard balanced XLR mic-level output

This lets me plug in anything crystal or crystal-signal-level-like and use this amplifier on it, just as with the carbon microphone, but for carbon-technology elements. In this case, I’ll be plugging in a piezo disc. But since that’s just the crystal, the real question becomes, what resonates it? What vibrates in the presense of the sound, causing the crystal to flex?

My initial idea for materials involved a lightweight, rigid plastic. I’d also thought briefly about metal, but decided that would be too heavy, and I was right about that. The bad news is, that also turned out to be true for the plastic – it takes too much energy to make it move, so it doesn’t move very much just from soundwaves, and the signal levels were really low.

This is the best I got, using the lightest of the “heavy” plastics. That recording was made talking into a small, clear rigid plastic sheet – I think it’s some sort of acrylic, but I don’t know. It came from Boeing! But does not fly.

I love distant-shortwave-sound of this recording, but that hiss isn’t an added effect – it’s amplifier noise from boosting the signal high enough to hear properly. So, obviously, that won’t work as planned – unless I need exactly this effect, of course.

Still, I’m thinking I could put it in front of a guitar amp or something else VERY LOUD. It’s modular, so there’s no huge reason not to keep it, and I have like 50 of these piezo discs. It also works as a gigantic contact microphone/pickup.

So I started working my way down material weights until I found something too lightweight.


THE HEAVY HEAVY DELRIN SOUND


The thin and tinny base of a styrofoam cup


FAILURES, ALL OF YOU! GET OUT OF MY SIGHT!

More and larger pictures on Flickr, as usual.

The lighter I got, the more response to sound I got, and the more signal – to a point, of course.

It turns out that the best weight is way closer to the styrofoam cup bottom than to any of the plastics I’d hoped would work out. A pair of thin foam dinner plates did actually rather well – I’d thought it was just one thicker plate, but no, it was two plates! – and I’ll try that again with a better (by which I mean actually shielded) test harness pickup, and plates that don’t have divided food sections.

And also, that styrofoam plate with the last 15mm or so of the “cup” still attached worked pretty darned well, without the echoy effect of a “cup” microphone. Some people want that; I am not one of those people. (But again, modular! And I have 50 of these piezo discs, I could make one anyway.)

This gets closer to the original construction materials used in the original crystal microphones, so really, I have no business being surprised here. I was just hoping that with improvements in crystal technologies that a heavier plate would work. But it’s just not generating enough signal output.

And that’s really kind of putting the kibosh on my whole boundary-microphone idea – at least, using this technology. Nothing strong enough to deal with the requirements of a boundary microphone – they’re quite large – is going to react enough to sound to give a decent amount of signal. Unless there’s some unexpectedly light and strong foam.

At least, not with these discs.

Maybe NASA has something I could, you know, appropriate. And I wonder if I can find that crystal material in, oh, one big giant sheet, and stick that to something strong enough. It has to come from somewhere
 
 


This is part of a collection of posts on building microphones and microphone-related kit, such as mic pre-amps.

Mirrored from Crime and the Blog of Evil. Come check out our music at:
Bandcamp (full album streaming) | Videos | iTunes | Amazon | CD Baby

solarbird: (Lecturing)

Building microphones is fun and seems to be of interest to readers, so here’s a collection post for posts about that! These posts discuss building both microphones, and, when applicable, their matching microphone driver circuits and/or pre-amplifiers.

Building a Carbon Microphone:

Related posts:

Building a Crystal Microphone:

Building a Ribbon Microphone:

Other microphone and preamp customisation/modification posts:

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solarbird: (korra-excited)

The last parts for the carbon microphone arrived yesterday! And once I got back to the Lair, I set about adding them to the circuit and building out the final version. Here’s a quick sample recording I’ll talk about more later.

I’m starting with the previously-discussed circuit, now taken out of the test harness and reassembled on one of the small breadboards. The new isolation transformer on the left – basically the outputs of the original circuit are attached to one side, and new outputs picked up off the other. This serves two purposes: first, it eliminates some kinds of hum noise if they start to crop up, and second, combined with 2K of resistance on the other side, brings the line-level(ish) output down to microphone level.

(These are standards which matter in a studio and … not many other places. XD )

The zig-zag in the resistors doesn’t serve any function purpose other than fitting into a smaller space – ideally, I guess I wouldn’t’ve been making needed values out of collections of other values? But I had what I had.

Signal flow is right to left in this photo. Underneath, at the top and bottom of the board, I’ve built wire rails to connect the components. That probably means I’m not really using the breadboard entirely as intended? I don’t even know. It holds everything in place and that’s definitely what I intended. XD

To house all this, I’m using an “experimenter’s case,” which is basically old-radio-speak for a metal box. XD It has soft metal on two sides, easily drillable and workable, and a hard case. I’m using one side for input, the power lamp, and the on/off switch; the other side is for output, or, as it turned out, outputs.

The carbon element (in the can) is connected to the driver/amplifier circuit via a 1/4″ TRS phone jack – like an old large headphone jack – with the two leads to the carbon element being on tip and ring, and the shielding ground being on the sleeve. (Tip, Ring, Sleeve: T R S.) That socket is on the left in the above photo; the middle component is a small LED, to indicate power on/off, and the right is a BIG CHUNKY POWER SWITCH. I love big chunky power switches. CHONK

For output, I quickly realised that I could have both balanced XLR output at microphone level, and line-level output on a phone plug, if I could find a way to isolate the chassis ground from the phone socket’s sleeve connector.

Normally, both being grounds on the same circuit, they’re connected automatically. Finding one that isn’t already connected is actively difficult! But careful use of electric tape did the job; I drilled the mounting hole larger than it needed to be, and basically lined anyplace the case and the socket would touch. Isolation achieved!

If you look for the blue and white wires, you can see where the TS (mono) phone plug is tapping the raw (line-level) amplified mic signal, just before it’s fed into the isolation transformer.

The transformer is really pretty optional – powered carbon circuit signals are pretty high as microphone signals go, and as I mentioned above, we’re actually reducing that signal to create the balanced XLR output on the other side of the transformer. But it’s nice to have the option of using line level, since it already exists. That’s what built-in sound inputs like on your laptop want, too, so there’s a point to it.

And here’s the whole driver/amplifier circuit, with a battery holder made of velcro.

Is that cheating? Holding the battery down with velcro, I mean. totally cheating I’m hoping it works out – I didn’t have a 9v battery case and it seemed excessive to try ordering one.

That LED power indicator? It’s warm white, left over from another project. I was planning on putting in your typical red LED, but realised that if they’d had a power indicator on one of these in 1932 or whenever, it most certainly would’ve been a little incandescent bulb, and it may and may not have had a colour lens. So I went with warm white, because period accuracy! Sort of.

The neat thing about the way this circuit works – and all carbon microphone driver circuits work – is how it points you right at vacuum tubes, and from there transistors, conceptually. It really, really does.

See, in tubes and transistors – which are both signal amplifiers – the input signal is used to create an amplified copy by controlling how much raw input power is let through, from another source. That’s why tubes were called “valves” originally; it’s because they are valves, electrically controlled, and regulating the flow of electricity from an input, just like the valve on your faucet controls the flow of water from the plumbing.

In this case, exactly the same thing happens yet again. But the input signal is sound pressure (how loud the sound is), which is controlling how much electricity is let through from the battery. And those changes in sound pressure – and therefore electrical flow – make the electrical copy of the sound waves.

Neat, huh?

Anyway, that’s the inside. Let’s look at the case!

I really like how chunky and primitive it looks. This is an old experimenter’s case; I’ve had a box of random cases in which I can build things for a while, and I don’t even know where I got this one, or when. If you saw it on the set of a 1950s television SF show, nobody would give it a second glance.

Always document your builds! You never know what might confuse people later. And by people, I mean yourself, after you’ve come down from the science-related memetic disorder high. I want at least the theoretical possibility of using this amp with other carbon elements, so writing down how the interface works is pretty important!

Except for the glare from the power light, I think this would be the Radio Shack Catalogue photo from, say, 1975:


Good, Better, or Best? Probably “Good.” It is just carbon, after all!


Or maybe this is the catalogue shot? Not sure.

Finally, here’s a test recording I made, using both outputs (phone/line level and XLR/balanced mic level) at once, hooked up to two different inputs on my board. I put both recordings in the same mp3; one’s on the left channel, the other’s on the right. The two tracks should be pretty much identical – being the same signal picked up at two different places on the board – and I wanted to see if that actually happened. Fortunately, it did!

Well, eventually it did. This is actually the second time I tried this, because the first time, I discovered that I’d managed to wire the two outputs up as electrical inverses of each other. Playing the two tracks back at the same time resulted in massive waveform cancellation. Which was hilarious, but also a good indicator; they wouldn’t’ve cancelled so well if they weren’t really similar. 😀


EXTREME WAVEFORM CLOSEUP

So that’s about it for this project! I’ll most likely do something to the ring to control the elastic better. And I’ll probably build a case for the whole kit, like I’ve done before – mics should have cases for protection! – but that’s a separate project.

This has been such a fun build, you have no idea. If you have any interest in this kind of DIY audio, I totally recommend this as a fun, easy project. Particularly if you don’t have studio gear, because you can look up the line level part of the output to damn near anything (including a PA system, I might mention) and it’ll work.

As always, more and bigger pictures on my Flickr account. And if you’re out of work, that’s a great time to listen to the new (NSFW lyrics) single! It’s awesome.

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solarbird: (Lecturing)

My carbon microphone is actually in a can now! I’m super happy with it, and yes, it works, even if most of the circuit is still in a test harness. The can itself does not contain anything important in the way of circuitry, though it does contain quite a bit of grounded shielding which is very important, and that shielding is carried forward out the cable, which is a TRS phone plug.

I made the decision to put the support circuitry in a separate box for a couple of reasons. First, the signal level is pretty high, so a decently-shielded cable should prevent most issues from being actual issues. Second, the support circuitry for these things tended to be external in the originals, so it’s period-accurate. Third, opening the can to replace a battery every 15 hours of use or so was going to be annoying; much easier to do it an an external experimenter’s cabinet.

And yeah, one of the downsides of this mic is the high power consumption. I thought about trying to tap phantom power, but from what I can tell reading up on it, the amount of power actually supplied – voltage aside – is dramatically lower than a battery’s supply and is not well defined, by which I mean is not defined, so… yeah. Batteries it is.

Anyway! I decided to make it look like a vintage carbon-element microphone of its era, only using elastic instead of springs. Springs look cool, but they’re also noisy as hell and create other issues, and it’s easy to tell that they would’ve used elastic if they’d had it just by how quickly they changed to using elastics as soon as they had elastics to use.

BUT SOLARBIRD, HOW DID YOU DO IT?

Well, first, let’s ask the eternal question: ah, junk shop, is there any build problem you can’t solve?


No. No, there is not.

If you’re wondering, that’s a vaguely-20s-looking kind of drink can holder in the middle, and I believe a hand towel holder designed to hang from the top of a door.

My only worry was whether the towel ring assembly was just screwed into the plate, or bolted to it; most excellently, it turned out to have been attached with a screw. So I just separated the ring from the existing base, sanded the attachment point down a bit to make it nice and flat, and attached it to a small metal L, using a rubber plumbing washer to make up the extra space.

Attaching to a standard microphone stand attachment is just as easy; unscrew one of those infinite number of cheap mic clips that are floating around every studio ever, toss the bit that holds the mic, drill out the hole in the L metal to be large enough, and pad with more plumbing washers.


Result!

Now the ring is ready to attach to any standard microphone stand.

Now, the can itself was a little more of a trick. This is all mechanical construction, not circuitry, since all that will be in an external box. But! There is some electrics, because given my particular… affinity… with RF (and radiating it, hi, it’s solarbird for a reason), I wanted a good heavily-shielded pickup enclosure.

Did you know you can buy adhesive tape made of copper? With conductive adhesive? It’s made exactly for this purpose. I love it. I started by lining the back, and peeling excess up the sides a bit intentionally. You want a good amount of overlap with this tape.

Lining the sides involves another ring of copper metal tape, with – again – overlapping tabs made of the excess height. Getting the height right is really simple – just put the tape in and cut inwards, using any common scissors – this may be metal tape, but it’s pretty thin, and no special tools are required.

After I took that photo, I realised I needed smaller tabs, so I went through and made another set of cuts, halfway between each existing cut.

Once you’ve fiddled around with it a bit, you’ll end up with something that looks like this:

Make sure the copper is well rubbed down against each other, so the conductive adhesive can really carry current without adding any resistance. Again, no special tools, a fingernail is fine – but make sure it’s well stuck down.

You might also notice in that photo, a small black line – I broke the tape, and fixed it with just a small piece to cover the gap. As long as you have well-connected metal throughout, you’ll be fine. We’re talking very low power with RF noise, in most circumstances, so you don’t have to worry about carrying power or anything like that.

Unless you have a tesla coil, maybe. That’s different.

Now, I also needed a grill for the microphone, and – importantly – it had to be a conductive grill, because I need that RF blocking all around the carbon element. I know, I know, some of you are going, “it’s a carbon element how are you doing anything to it?!” and all I can say is I have recordings and I have to ground myself with a wrist strap if I’m using AKG microphones, and again, supervillain.

Fortunately, a material that serves this purpose quite well is common and cheap: aluminium window screening! I’m kind of annoyed with myself, because I threw away a bunch two weeks ago – used but still clean and good – because I had no thoughts I’d need it. What was wrong with me? I can’t even tell you. Moods. So I had to stealbuy some. Fortunately, it’s pretty much dirt cheap.

I got a ring of heavy flexible rubberised foam to make a structural ring, and measured the right size just by pushing the screening into the bottom of the can until I had good edges. Since it is window screening, it has a lot of room to compress, and that helped. You want that excess screening material, for reasons which should be obvious momentarily.

In the above photo, I’ve sized the screening material, and am getting ready to make a ring of copper tape to surround both the inner and outer layers of the support ring. This is partly structural – you can see that my support ring is not a single loop, but a bent straight piece – and partly to help make sure of good, solid contact between the metal screening, through copper tape, to the interior copper shielding of the can. Make this part a little too large, if anything, and you end up with a solid pressure-contact connection.


Swaaaaank

Holding the carbon element in place is also a job for foam. In this case, I have some high-density impact-absorbing foam left over from my case making projects earlier, so I just used that. It can be a very rough cut, as long as it’s just a tad bigger than the ring it’s going into. It’ll compress, and that provides a little more outward pressure to make the grounding contact between the grille and the interior shielding better.

You’ll also note inside the can, against the back, I’ve placed a spacer ring. This keeps the grille’s support ring from going too far into the can; it’s just a physical element, since you want the carbon element nice and forward, and not sinking into the can where sound would get echoey.

What you can’t see is an important step I … didn’t remember to photograph. Sorry! And that’s drilling a hole for the cable. The cable is three-conductor; two signal leads (which connect to the two contact points of the carbon element) and one shield ground. The shield ground gets soldered directly to the copper tape, which is why you use copper metal tape instead of some other metal. This is a little tricker than you might expect, mechanically; I had to use higher temperature on the soldering iron. I think it mostly has to do with soldering wire (physically complex, wicks well) to a flat surface (physically simple, does not wick well). Just take that part as read.


[Win95TADA.wav]

Some of you might be looking at this picture and going, “…wait. The carbon element is right up against the grill. It’s touching, and metal, and isn’t that a problem?”

Well spotted, you! It would indeed be a problem! I solved it by cutting out a couple more layers of plastic window screening – also left from another project – to provide an insulation barrier between the metal screening and the actual pickup element. If you don’t have any of that, hosary would do fine – the same material used in pop filters. Acoustic transparency is important here, of course, but to be frank – less so than usual.

“That’s not like you.” Yes. But think about it, I mean, what’s a telephone use? Oh yeah, THICK PLASTIC WITH SOME HOLES IN. Does it hurt the sound? NOT VERY MUCH, because it’s a carbon element with a range of around 300hz to 3500hz, maybe. So you can afford some loss in the high end, because what you don’t lose, the mic will lose for you. And this screen material is plenty acoustically transparent for these circumstances. So would be hosary, or the right foam, or all sorts of other things. Just, you know, use good judgement.

Anyway, the build stuck on hold – ON HOLD! HA! – for a couple of days as I wait for the 600ohm isolation transformers to arrive. They aren’t essential, necessarily, but do reduce RF noise and hum in some circumstances, so I’m going to use one. I’ll post more when I’ve got more done. I’m really pleased with how it’s coming along; this is fun.

Bigger pictures on Flickr, as usual.

ps: People were asking for a sound sample. This is from the test harness, before I built the ‘can.’ New recording sample next time.

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solarbird: (made her from parts)

I have a waveform! I did a bunch of testing of various parts and such, discovering that the carbon transmitter (microphone) I had was indeed fully functional, and really, it came down to “not enough voltage.” 1.5v is pretty borderline for carbon microphone power, so that’s fine.

The waveform is kind of lopsided, but that’s because this test harness doesn’t have the balanced output yet; I’ve ordered the balanced transformer, and that should help. It’s also a bit noisy – here’s a sample – which is partly related to SHIELDING WHAT IS SHIELDING because it’s a test harness.

Talking of, here’s what version one looked like:

This is a direct implementation of the first half of the circuit described in this instructable, which runs off a 9V battery. Once the rest of the circuit is added, it’ll have balanced output, which is pretty snazzy.

This is a closer view, and also after I added an LED, because hey, LEDs!

After that, I tried a smaller capacitor, and that’s working fine – mostly, I’m just picking from what I’ve got, which goes along with what the circuit designer described.

I’m going to play more with the circuit a bit, pending getting the matching transformer. And some shielding.

And, of course, the can. 😀

ps: this harmonica “bullet mic” looks pretty cool too.

Mirrored from Crime and the Blog of Evil. Come check out our music at:
Bandcamp (full album streaming) | Videos | iTunes | Amazon | CD Baby

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