Solarbird (solarbird) wrote,
Solarbird
solarbird

Project Kohaku A-B-C

I made another thing! A magnetic (electric) Irish bouzouki pickup, the kind used on electric guitars, but with some extra features. I retconned a project name for it (Kohaku A-B-C) because it has three primary modes – “single coil,” “humbucker,” and “electric/acoustic mix,” which to be honest is kind of two modes depending upon the single coil vs. humbucker setting, but Kohaku A-B-C-D is too long and didn’t sound enough like a JDF anti-Godzilla plan.

Sounds!


Originally I was just going to do a basic wire-up with a level knob, but then I found out that humbucker pickups gave you separate access to both coils, and so can be used as a single-coil pickup as well as in humbucker mode. So that meant adding a switch. Which means it’s probably worth doing a tone knob while I’m at it. And while I was thinking about that I realised there was no reason I couldn’t also build in a tap to the extant acoustic pickup, which means I should also add a little mixer to control relative levels of the two pickups.

So I did! That was a good idea.


The two red knobs are the mini-mixer for the electric (left) and acoustic (right) pickups. Infinite relative levels! Or close enough. The two big black knobs are combined output level (left) and tone (right), the little switch is tone disable switch, the bigger switch changes the pickup mode – humbucker or single-coil.

I’ve had a bunch of those black rocker switches for a while, but I rarely use them because you need to cut a fairly precise rectangle for them to snap in correctly – there’s no screws or anything. Hearing that [CLICK] when you do it right and it pops into place and is straight and not loose at all or anything is so satisfying.

The pickup is held in place in the soundhole basically by foam and friction. Here’s the first test sitting, after I’d added the high-density foam to the pickup itself:


That was almost enough by itself, but not quite. I ended up adding a backplane and some spacer elements, as it had a tendency to rotate in place without those. The hot glue is mostly there to be cable stress relief:


The project box is an old Radio Shack room monitor transmitter – basically, a baby monitor. I don’t remember how I got it or anything. Regardless, I tested it a few years ago and it’d gone bad, so I gutted it and kept the cases for projects. I think it cleaned up well!

I can’t find a picture of a truly unmodified example, but I did find a decent picture with this mod where that modder kept the words “REALISTIC” and “FM WIRELESS ROOM MONITOR” on the box. I’d wanted to keep the REALISTIC logo, too, but I couldn’t – the knobs wouldn’t stay in place flat with the word still there, so I scraped it off with an xacto knife.

I did keep the big TRANSMITTER label though. That seemed important.


Here’s that little rectangular switch. [CLICK] into place. So satisfying. Looks factory. ♥


Here are the large-block components in place, without the wiring, and also without the tone knob bypass switch which was actually a later addition. (One that turned out unnecessary – 800K resistance and infinite resistance are pretty much the same as far as this tone circuit goes.)


The circuit itself is very simple. The larger switch controls which lead from the pickup (humbucker or single-coil) is fed into the electric pickup side of the mixer. The two mixer knobs are just straight-up variable resistance pots, as is the combined-output level control. The tone knob is based on the 1950s-1960s Les Paul-style electric guitar tone knob, only with a smaller capacitor which goes pretty well with the zouk. And the tone-knob enable/disable switch is just a ground lift on the far side of the capacitor and variable resistance pot.


Now I just need to find some way to make the controller stay attached to the face of the zouk (or any part of the zouk really) without making any change to the zouk itself. Maybe a suction cup?

I wasn’t even really thinking about that part when I started this project, past “keep it small so maybe if I want to think about it later, I’ll have the option.”


It almost looks like some kind of foot pedal, doesn’t it? The reason the controls are so large is just so they’re easier to grab without looking. I’m already controlling this thing by feel – if I can come up with some way to attach it, I think it’ll be legitimately viable as a stage device. It’s certainly no fussier than that piezo pickup I made for the octave mandolin, and I’m using that.

So – yeah! Kohaku A-B-C: much more fun than I expected. If you want to make one, Here’s where you can get the pickup bar, the only thing I bought new. The pots are all 1M variable-resistance linear pots, the single coil/humbucker switch is type SPDT and should be pretty clean since the signal goes through it, the capacitor is… 14nF film cap, because I had it and it was handy, and the tone bypass switch isn’t worth doing but if you want to regardless just use anything that’ll let you connect a wire to ground – it’s not in the signal path so you don’t have to worry about quality. The knobs were from the Radio Shack bankruptcy sale at 90% off, and since they’re going through another round of that now, maybe you can get some 90% off too. Or just use the metal posts for an industrial look, it’s not like you need the knobs.

As always, higher-resolution pictures are on Flickr. Have fun, and if you build it, let me know! ^_^

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