synthgeek's blog

Found this thing at a second-hand store cheap- since it’s made out of clear(ish) plastic, I could see a couple of resistors on the circuit board, and thought it would be worth checking out for the price, in case one of them was a pitch control. Score! It was.

Below is a shot (kinda blurry, sorry) of the circuit before bending. The resistor marked “R2″ is the pitch resistor. You can also see the backside of the built-in speaker:

The rest of the circuit wasn’t very exciting, the sound-making part was a blob-type IC. The other possible bend would have been to add external play triggering, but retriggering while it was already playing didn’t interrupt what was already playing, so that wasn’t super-exciting either.

What I ended up doing was taking out the existing resistor, replacing it with a 10k (it was 55k), and adding a 500k pot inline. Here’s a shot of the board after modification, notice the heat-shrink tubing around the resistor for added strength:

I ended up having to add a second 10k resistor to the opposite side of the pot, as 10k wasn’t enough resistance to keep the chip from crashing (easily fixed by cycling the power). Of course, a 20k resistor at the board would have worked too, but I’m fresh out anyway. I also added touch points (using screws) for changing the pitch- they also cause some glitching under certain circumstances, sometimes leading to crashes, which again can be easily remedied by cycling the power.

I also added an output jack (with a 1k resistor on the board end of the wire)- I had to go with 1/8 inch, due to size restrictions imposed by the enclosure. I also had to grind away some plastic which was getting in the way of the jack.

Some shots of the finished piece:

…and here are some sounds. First up, a dry recording, messing with the knob & touch points:

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Next, processed through the LM567 amplitude modulator in Phoenix, then a lowpass filter, and a delay:

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This one is just the Sorry Pawn with delay:

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