synthgeek's blog

Here’s a couple more recordings from Mimsy Modular, showing some sounds made using the CV input on the APC module. These two recordings also show some of the interesting randomness & instability which is made possible by the voltage starve effect.

Up first, the APC being modulated with the output from osc 2 of the other module:

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And now, the APC being modulated with the output from the Coffee Can of Doom:

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Well, it’s done, and the last bit of experimentation yielded some unexpected results. During my initial tests with using the other side of the second 556, I accidentally found a way to use it as a pseudo-noise generator of sorts. I noticed similar behavior on the APC side at certain settings, but thought it had something to do with the interaction between the oscillator and monostable- apparently it’s possible without the monostable as well.

There are various strange interactions between these new controls and the existing ones- for instance, the new switch not only acts as a pitch drop for the new osc, but also enables the touch points on the first one.  There also seems to be a sort of cross-modulation effect going on (see the audio example further down). All in all, things seem rather unstable with the second module now (certain things seem to make the second half stop working until the power’s cycled, various other strange things happen), which leads me to believe I’ve done something wrong- but it also makes things interesting, so I’m going with it.

Another “happy accident” that happened was that I came accross a nice touch point to make use of the spike- in fact, I found two, so I added a second spike.  I also added some other decorations. Yep, ugly as hell, just like the sounds it makes. :)

Back panel- there are now two outputs for the second module, as well as the output and CV in for the APC:

And now the audio (random touching & twiddling)- first “osc 1″ of the second 556 module (note the sort of AM-type ringing):

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and then “osc 2″:

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This update includes some cosmetic changes, as well as a voltage starve mod (the knob on the top) and a CV input to the oscillator which drives the APC (the silver knob on the “faceplate” controls its level). I’ve decided to name this synth the Mimsy Modular, in honor of the inventor of the Stepped Tone Generator the APC is based on (Forrest M. Mims III), and in reference to my favorite poem (Lewis Carroll’s “Jabberwocky”).

The black stripe is electrical tape, the spike is just something I had in a junk drawer- though it currently serves only as a decoration, it may be used as a touch point in the future. The batteries are now held in place with metal clips which are hot-glued to the box. The metal strip with the voltage starve knob is also held in place with hot glue, and also holds the on/off switch for the APC in place.

Here’s a shot taken during the latest update showing the output of the right-hand module being fed into the APC’s CV input:

And here’s a recording of some knob twiddling with the second module plugged into the CV input, no effects:

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My next plan is to wire up the unused side of the second 556 in a similar fashion as the first, but pitched lower. I will also be trying to find a way to make interesting use of the CV inputs.

I ended up using another 556 for the second “module”, right now it’s just wired up as a simple tone generator with a single frequency knob, an on/off switch, and a high/low range switch. I also added the capacitor bank to the APC side, with a momentary switch (button) for each of the two caps.

Nice thing about this box enclosure- easy to open up for modifications:

Hole shot:

Build of the Atari Punk Console circuit using the Kaustic Machines schematic, housed in a nifty-shaped cardboard box.

As you can see, plenty of room left on the perfboard for experimenting with mods. I’ll definitely be adding a capacitor bank as seen on the Get Lofi APC boards, and a voltage-starve pot. I’m also planning to put a 566-based oscillator on the other side with a seperate output to use as either a second sound source or a CV for other gear.

The pots I was waiting for were in the mail today, so I did the first round of mods. These mods are all documented elsewhere, so I won’t bother repeating all the info here. I just did the noise level & “Moog slayer” mods for now.

Here’s a shot of the main board with the trim pots for the filter cutoff & resonance and noise level removed:

Here’s shots of the new knobs (filter, then noise level):

One hint which I don’t remember seeing online elsewhere is that you want to use a reverse-action knob for the noise level.

Next I’m going to replace two trim pots on the delay board with front-panel knobs:

The knobs will go to the right of the noise level knob, in the middle of the two blank spaces, like the noise knob.

Still waiting for the parts to mod/fix the Poly-800, so I decided to do another quick project in the interim: the Coffee Can of Doom! This is a circuit-bent instrument based on a toy soundboard called the Doomsday Device that makes ticking sounds & beeps an alarm, like a bomb I guess.

Here’s the board, pre-modification:

Here’s a pic of the board with extra parts/wires soldered to it (this is another board, not the one used in the CCOD- the only real difference is shorter wires for the jack & switch):

And here’s the Coffee Can of Doom:

The Can is “played” via the contact points on the lid. Here’s what it sounds like (just a recording of randomly touching various points and combinations thereof):

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Came across some cool stuff while looking for the parts to mod the Poly-800. I guess most people know about Jameco, I found some better deals at these other places:

Electronic Goldmine – surplus parts. Limited selection, but really good prices on some stuff. $10 min. order.
Futurlec – good prices on pots & knobs, good selection.
Pedal Parts Plus – seems like a good source for stuff that’s harder to find elsewhere, like stomp-type switches.
Harbor Freight – not for electronics supplies per se, but a good source for cheap tools & other supplies related to electronics (drills, multimeters, etc.).

Got some goodies for other projects too, so after I’m done with the Poly, expect more fun-with-electronics posts.

This should be required reading for anyone entering the world of digital audio & plugins, as the basic concept applies to more than just equalizers. From the signaltonoize blog:

All digital parametric EQ’s are the same.

The subject came up in a conversation today, and this guy puts it better than I ever could.

My Poly-800 MkII has developed a problem where the noise source is always on at full volume. Neither the envelope or volume parameter has any effect. The envelope still works on the filter.

I’ve got it pulled apart to see what I can do, if anything (will probably require replacing a chip I’m thinking, not sure)- and while I’m in there I’ll probably do some mods too, starting with the moog slayer mod. I’ll be posting pics as I go. The first set of pics are the innards before any poking around (other than some air dusting/vacuuming- it was pretty dirty in there):

main board 1

delay board

delay board- no flash

long view

main board above

The project may take awhile, since I’m not sure how easy it will be to find replacement parts. If it requires buying another Poly to cannibalize, then it will definitely be awhile before the repair gets done. However, the parts for the mods are easy to come by & cheap, so that may get done first.