synthgeek’s blog

Fixes some errors, and adds some minor enhancements.

Here’s a video of Mimsy, Phoenix, the Modutronic Messmaker, and the Dirty Cow amp all making noise together, along with the Blue Lantern filter:

I recently came across some nifty schematic and PCB design software called ExpressPCB- the download includes seperate programs for schematic drawing (ExpressSCH) and PCB design (ExpressPCB). I haven’t tried the PCB part yet, but here is my first schematic (click for full-size):

This is my first schematic, so there may be errors. Both of the basic circuits are well-documented elsewhere, however, with only minor changes in my implementation- so if you build from this and it doesn’t work, google “Atari Punk Console” and “555 oscillator”. I just wanted to try out ExpressSCH, and this seemed a nice, quick way to do so.

Having learned a few things since building this, there are a few small changes I would make if I were to do this now. I may post a “revised” schematic eventually.

First, two Phoenix vs. Mimsy videos:

One of just Phoenix:

…and one of just Mimsy:

Here are a couple of longish (8+ minutes) recordings made with the Phoenix/Mimsy combo. Not to be confused with music.

The first one is the raw dog: no effects, just a single output into a mixer channel. There are some bits in this one that do a fine job of demonstrating the fun that can be had using Mimsy’s 555 osc as a modulation source, while modulating it with the Phoenix LFO. With the voltage starve in the mix, some interesting semi-randomness is possible.

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The next one gets the Kaoss pad and rack effects in on the fun:

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I decided to try something different, this time with a 555 timer chip. I removed the second side’s synth (the non-APC one), and replaced it with a super-simple 555 osc, very similar to this one from the Get Lofi site.

The controls are now arranged thusly: on/off switch at the top, second switch for choosing triangle or square wave, red knob for voltage starve, upper silver knob controls frequency, lower one controls CV input level.

This osc has a very wide frequency range, from sub-audio LFO freqs to very high. Here’s some audio which shows this range using this osc to modulate the APC side. The very first bit demonstrates the LFO sweeping from low frequencies into the audio range.

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In this recording, as with the last, Mimsy Modular is being fed into one side of the Simple Analog Multiplyer, and the Phoenix APC osc is feeding the other. The Phoenix APC is also modulating the Blue Lantern filter’s cutoff frequency (the orange & blue unit in photo below- not one I built). There are parts of the recording where the filter itself is also being used as a sound source (self-oscillation ftw). No other effects were used.

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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.