the bridge pickup improved

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.

another weekend of noodling with electrics

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:

three-gear meshes that actually work

A nice little bit of fun on Friday. You’ll see, pretty often, illustrations of gears for some sciencey or engineering-invoking illustration or logo, and they’ll be all shiny and pretty and stuff, right?

Problem is, those gears can’t turn. They’re wedged together. Play with it in your head, you’ll see one gear is forced to turn in two directions at the same time, and of course can’t.

So Numberphile – who has a youtube channel – decided to come up with some three-gear systems that actually work. They’re really cool. Enjoy:

not so much a primary lair, but…

A new lair is on the market! Yes, it’s small, might be a good starter lair for the aspiring supervillain, but I’m really thinking more a… rural redoubt, perhaps. And it’s got extra bedroom space for the minions you might bring along.

As I understand it, the Tesla Death Ray tower behind the lair is included, so that’s definitely added value there. A starting supervillain wanting to use this as a primary lair should convert it to a shield dome emitter, but, of course, that goes without saying.


Not Fancy, But Strong – that’s all rebar and poured concrete!


Features include a spacious meeting room for discuss your plans.
Note the built-in control panel by the couch –
I presume that’s for the ejector chairs that fling your enemies into the fire pit.

a close call with hiatus

Yeah, yesterday was fun.

Night before last I started having these visual effects in my left eye. Now, I have a history of repeated childhood head trauma, and visual effects are real bad because it turns out when you have that trauma history, your retina can start to disintegrate in adulthood. That’s how I lost most of 2014 to repeated eye surgeries.

So when I started seeing these odd effects in my left eye, some of which were similar to previous effects, I was pretty much freaking out, because Oh Shit Not Again. But they weren’t exactly the same as the previous times, and what I was seeing also matched the description of a strange and rare migraine variation called ocular migraine, where it’s basically a migraine, but entirely confined to your retina and optic nerve.

And that’s there the ophthalmologist went, too. The good news is: no surgery. The other, mostly good news: it’s probably a clean bit of vascular membrane separation. This happens all the time, including to you. If you see floaters in your eye for a while? That just happened to you.

For most people, it’s harmless. In large cases, there’s a small (2-3%) chance of retinal involvement, and that’s not at all good – if your field of vision changes, that’s the sign you need to see someone immediate.

For me, by contrast,, that percentage had so far been 75%, not 2%, because if there is the outer edge of a bell curve to be found, I will goddamn well find it.

Those odds now down to 60%, which is much better. He examined the hell out of my retina and couldn’t find any sign of disturbance. It looks healthy as all hell.

Which is why haven’t actually ruled out ocular migraine either, because what I’m seeing with the neon-like lights business actually fits that better. If I didn’t have a big new floater, that’d probably be the only thing under consideration. Good part of that is: nobody understands it, but it’s confined, and has no symptoms – no headache, even – other than the optical effects, and the prescription is “well, just put up with it, it’ll go away. And then come back, and then go away, but it doesn’t hurt and generally won’t change much.”

The doc doesn’t think anything will happen, I just have to keep an eye on it – EYE on it! HA! – for six weeks to be safe, and I have a follow-up appointment in July. If something retinal were to happen, well… I’d be back on hiatus.

But not today.

I gotta say, I have never been so happy to be working on a drum track all my life. 😀

i learned something today

I guess it’s obvious in retrospect, but Monday I learned that a drum machine is basically just an overgrown sequencer. I kind of wonder if the original progression was the opposite way.

This is new to me because I’ve never used one before – all those drum tracks on previous work is microphone on live drums. Timing edited, sure, but live. But now I need a drum kit for a thing and I’m not a kit drummer and don’t have a drum kit, so OFF WE GO.

I’m using Hydrogen. It’s pretty cool so far. And really easy to use and comes with a lot of sampled drums. I wish it had arbitrary label marks so you could make notes on where you are in a song other than by measure count. But maybe you can and I just haven’t found it yet.

aaaaaait has a mixer i just found the mixer i was trying to figure out how i would do this later in ardour and i don’t have to i can do it here 😀 \o/ \o\ /o/

I love discovering new useful tools. Have you discovered any lately?

when last we left our intrepid crystals

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.

confused by background radiation

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.

presumably the crystal gems would use this kind of microphone

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.

the kalamazoo gals: gibson guitar’s erased women

It’s a common story – lots of women enter the workforce during World War II, doing all the jobs normally restricted only to men, before millions had to go off to fight Fascism. Then the war was won, the soldiers came back, the women were forced back out.

But, at least, it was acknowledged, and, at least, some credit was given.

But not at Gibson Guitar. They officially say that they shipped no instruments during World War II at all – not a one. But that’s simply not true. They did – they made and shipped thousands of instruments, with a wartime workforce of women. Some even went with GIs overseas.


Women instrument makers, Gibson Guitars, Kalamazoo, Michigan

Apparently, management decided that people wouldn’t want instruments made by women, so they erased the Kalamazoo Gals from history. When law professor and music journalist John Thomas got a hint there had actually been wartime production, and found out the story, the acoustic department was initially very interested – and then corporate found out he had been digging, and started threatening him for revealing it. It’s fascinating:

Women guitar makers scratched from Gibson history
By Ryan Grimes

Women are constantly being erased from history, including music history. Sometimes more aggressively – and pointlessly – than others. Never forget that.

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