synthgeek's blog

Based on this schematic found at the Experimentalists Anonymous archives, using a Texas Instruments NE5532 (dual op-amp, interchangeable with the LM358). This is a voltage-controlled triangle/square wave LFO. Here you see the perfboard layout, minus the speed control pot. The schematic calls for a 100k pot, I used a 500k.

Here’s the panel- on/off switch, speed knob, and two outputs (triangle and square):

Here’s some audio, similar setup as the last one, but with the addition of filter modulation via the LFO as well:

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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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A few posts ago, I mentioned the passive audio input. This is simply a 1/4″ jack wired to a 1/8″  jack with a passive volume control in between.

I have also added a passive “mult” panel to one of the jacks on the far right. This just has an additional two 1/8″ jacks wired up to carry the same signal as the other two.

This was an ultra-simple 10 minute project designed for use with solderless breadboard experiments. All there is to it are a couple of 1/4″ jacks and a SPST switch with holes for the wires to come through.

I used the clipped-off bits of component legs soldered to the ends of the wires to create connectors that can easily be used with a breadboard:

A recording of SAM being fed with the Phoenix APC osc and Mimsy’s APC:

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There are things you could do to make it sound more like a real ring modulator, but I’m planning to build one of those too, using a completely different method.

As mentioned in the previous post, this is a very simple device- 1 IC, 2 resistors, 2 capacitors, 2 pots, and 3 jacks (2 in, 1 out).

I had read that the AD633 has a very short break-in period when first fed power, where it gets very hot- well, they weren’t kidding. In a few short seconds after hitting the power switch, I caught a heavy whiff of the unmistakeable smell of hot electronics. It was so strong, I expected to see the magic smoke wafting up- all was good though, and SAM was born. Audio to come soon.

I decided to make the first module a quick & dirty APC based oscillator.

I decided to make this module the home for one of my newly-aquired touch-plate switch panels. You can see it in the above photo, beneath the output jack. This takes the place of the cap-bank switches on Mimsy Modular. To the left, under the power switch, is a knob I plan to use as a voltage starve for the APC. To the right is a passive audio input.

I haven’t actually hooked it up to the power supply yet, just tested it with a 9V battery.

The next module I’ll be building for the Phoenix modular project (when the parts finally get here) is an amplitude modulation device based on the AD633 chip. I’ll be basing the AM device on a schematic found at the Experimentalists Anonymous archives, the Fatman Simple AD633JN Ring Modulator. As it turns out, this is little more than the basic multiplyer schematic shown in the data sheet:

I’m going to call it SAM, for Simple Analog Multiplyer.

Sorry for the terrible photo quality:

Simply called “Pocket Game Player”, this is a simple black & white-LCD mini game thing with several simple games onboard, including a version of the classic Atari tank battle game. The main guts are in one of those blob-style IC’s, and some probing revealed no real interesting bends, though I was able to get the pitch to drop, and to crash it, resulting in a stuck note.

There are some possibly useful bits- the buttons are on seperate daughterboards, and use those touch-plate style switches, which I’m betting I can repurpose for some other device.

Another interesting thing, though not actually useful, is the display. You can’t tell from the photo, but rather than tiny solder connections, it uses some kind of three-layer rubbery thing on either side (a black layer between two pink layers). The display was just pressed against the PCB contacts, and held in place by the pressure of the casing. I hadn’t seen anything like that before.

Figures- their prices are significantly lower than the competition in many cases- however, it’s been over 2 weeks, and I’m still waiting for my parts. My last order from Jameco took only 4 days to arrive. Heck, I got my stuff quicker from Small Bear, and I’m pretty sure that’s just one guy.

I’ve never claimed to be a patient man.

Some research recently made it apparent to me that the power supply from my ESQ would be a better choice to use for the Phoenix modular project, since it already has a bipolar 12v supply, as well as +5v and unregulated +9v- so I won’t have to modify it at all. I’ll use the other 12v supply as a bench supply.

The frame/rack arrived the other day, and thanks to a shelf unit from Kris already has a temporary home in my studio. Here’s some photos- a close-inside shot of the frame from the side, and a picture of it in its new habitat:

The next photo shows the PSU and the start of a temporary faceplate I’m laying out on cardboard:

On the left is the power switch, on the right 3 jacks which will be part of a 1/8″-1/4″ patch bay. I’m just going to wire a few 1/8-inchers right up to the 1/4″ to facilitate interfacing with other gear (I’ll be using 1/8″ for the modules).

The transformer and PCB for the power supply are screwed down to the wooden shelf, which slides out like a drawer for easy servicing. The PCB is attached  to a metal L-bracket, which is why is sticks up at a nice 90 degree angle like that. I’m planning to scavange the casing from a computer power supply to provide a stable mount for the 120VAC connector and a chassis ground. I’m trying to build it in such a way that everything will fit inside the frame when it’s done, but for now I just want it to be as easy as possible to work inside the frame.

In other news, the SID chip trade didn’t quite go according to plan- the chips he had all had dead voices, so I’m getting some other stuff which will be useful in other projects instead. What I’m getting will be more immediately useful, so it’s all good.