Yamaha PSS-130- owned from May 2003- present, bought for $53 with PSS-570
The PSS-130 I think represented the lowest range of Yamaha keyboards at the time. It seems to have the same hardware as the earlier PSS-30 in a different case, and I think the PSS-120 is nearly the same thing, though I haven't verified it.
There are 8 sounds (duoponic pulse waves with low-resolution envelopes, and vibrato on 2 sounds) and 8 rhythms (very short loops, a lot of similar sounding rhythms, square wave for bass drum and tom sounds, noisy metallic cymbal sounds, etc.). And there's a short monophonic sequencer, which must be played with a rhythm, though it's possible to change the rhythm while the sequence is playing back. It's possible to play over the sequencer, using a different sound, and both voices. So really it's 3 voice polyphonic, but one voice can only be accessed by using the sequencer. Everything is selected by membrane switches, which means that sliding a finger across the instrument select switches while holding a note down can produce a very interesting effect. Unfortunately, the keyboard and the panel buttons are scanned by the same circuit, so only one key can be held down when doing this. There are 4 volume control levels, none of which are really quiet, and the loudest overdrives the amplifier. Also there is no audio output.
There's really only one chip inside, a YM2410, and also an LM386 amplifier on another board. It's very simple, so I figured out what all the pins do by following the circuit board traces. I found that the tones and the rhythms are output on separate pins, and that the only point which produced glitches of any kind was the clock input pin (though it really doesn't do anything interesting). Also, it's possible to clip the amplifier (pretty nasty sounding) by shorting out the gain resistor. So, I added an output (which switches the speaker off), a glitch button (pretty boring but I did it anyway), a distortion knob (I used a 5K potentiometer to replace the original 3.9K resistor, though a 1K potentiometer probably would have worked better as most of the range doesn't do anything), and independent outputs for the tone and drum sounds (inserting a jack removes the sound from the speaker/main output, and the jacks come directly off the chip, which bypasses any capacitors- so the sound is much harsher and unfortunately is also DC).
The sounds are decent if you like Nintendo-sounding pulsewaves (particularly the Piano and Harpsichord remind me of NES sounds) and very low quality drums. Unfortunately sometimes there is also a whining sound from the button scanning circuits in the output.
pictures:
links:
A page detailing the PSS-30 can be found here: Yamaha PSS-30
Yamaha has user manuals for nearly all of their products available here: Yamaha Manual Library (English)
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