A drum

One type of module I’ve been missing so far is drums. You can get drum sounds out of general purpose modules, but putting together a drum kit is easier with specialized modules.

I went looking and found a couple good candidates at Barton Musical Circuits. I bought a PCB and a panel for each and started sourcing parts.

First the Analog Drum. The PCB’s pretty reasonable, through hole, not crowded, cleanly laid out.

As for the panel? Minimalist. What Barton sells are pieces of unfinished aluminum with holes drilled. He writes, “I chose to do unfinished panels over finished panels to encourage creativity and self expression. Paint them, sticker them, engrave them, finish them however you want!” How he wants, to judge from the pictures on his site, is pretty lowbrow. You can get a more refined panel from Modular Addict. But it goes for $20 before shipping. The unfinished ones from Barton are $8. Yes, I bought a $15 panel and paid $5 for shipping from Magpie Modular last year, for the NLC Timbre, but that was a sale price and less than what NLC charges for their much less attractive panel. In both cases my inner cheapskate was happy.

The Analog Drum consists of a simple dual envelope generator, a simple VCO, and a simple VCA. Lots of simple: stripped down to what’s needed for a drum. The EG generates two envelopes at each incoming trigger, both with fast rise; there are knobs to adjust the two release times. One envelope controls the VCA: silence, loud, quieter, silence. The other goes to the VCO CV input to make the frequency decay from its initial value. There are knobs to control how much the frequency changes, to set a baseline frequency, and to attenuate an external CV, controlling the baseline frequency. That CV is one input and the other is the trigger (or gate, it only looks at the initial rise), and there’s one output.

I did take issue with a couple of design decisions. There are 10R series resistors on the power buses. I’m not by any stretch of the imagination highly knowledgeable about electronics, but Matthew Skala of North Coast Synthesis does seem to be, and he’s not impressed with that kind of design. Granted, part of what he grouses about is “filtering” with resistors but no capacitors, and here we do have the usual 10µF capacitors to ground. Still, he argues, a better use for those four holes in the PCB is to install Schottky diodes as voltage reversal protection, and I’ll buy that. I put in 1n5817s in place of the 10Rs. Yes, I’m using shrouded headers, which should make it impossible to plug the power cable in backward. But it doesn’t make it impossible for the power cable to have been made backward!

The other thing I found strange was that Barton specifies 0.01µF capacitors for bypassing. Pretty much every other synth module I’ve ever looked at uses 0.1µF and that seems more generally what people say you should use, unless you have a touchy filtering situation where you need to do the analysis and figure out which caps, maybe multiple values, are optimum for the frequencies you’re concerned with. Now, it’s definitely not critical here. Sam Battle (LMNC) always says go ahead and leave the bypass capacitors out if you don’t have them and don’t want to bother with them, and when I built the MFOS VCF at first I was out of 0.1 µF ceramics and so omitted them, and I never noticed a problem. I did go ahead and add them when the next Tayda order came in.

Anyway, I substituted 0.1 µF for 0.01 µF next to the ICs. There’s a fifth 0.01 µF as part of the pulse conditioning circuit on the trigger input, and I left that as is.

For the front panel, I decided to try a procedure recommended by Ray Wilson, one I used when I built the Weird Sound Generator. I drew up a design in Inkscape, printed it (in color at the local office supply), and had it laminated. Then I used contact cement to affix it to the aluminum, cutting to size and cutting holes as needed. I’m not that crazy about the result. It looks okay, but it’s very glossy and shiny. Also, Barton’s panels are already fairly thick (2 mm) and the addition of the laminated paper made it very difficult to screw the nuts onto the jacks. I managed the first two but the third gave me so much trouble, in the end I tried a different style jack to see if it would work better and it did.

Other than that the build went smoothly, nothing went in backwards! Well, nothing got soldered in backwards. I checked for power shorts, checked power connections to the IC sockets, plugged in the ICs, connected to power, and turned it on. It worked.

I’ve only played a little with it but I like it. The FM drum is next.

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