Yamaha PSS-570- Owned from June May- present, bought with PSS-130 for $53
Yamaha loved FM synthesis in the 80's, and the lower end FM chips made it into the portable/home keyboard market. Most of these only have presets, but a few PSS and PSR models are editable. There seem to be 3 basic types of editable models- the 360, 370, 460, 470, 560, and 570 models use sliders with 5 steps, the 380 and 390 models use sliders with 8 steps (with a slightly different selection of sliders), and the 480, 680, and 780 models use digital editing and have midi. I don't think it's really worth going into all the details, but each model is a bit different and has its own advantages and disadvantages.
The PSS-570 has 12 rhythms and 21 "orchestra" sounds. It has 9 2-operator voices. Sounds can be edited by pressing the digital synthesizer button, which generates sounds based on the postions of the sliders, or by moving the sliders while playing orchestra voices. Not all of the parameters are editable, so editing the orchestra voices sounds different depending on what voice is selected. The parameters are wave (modulator frequency), spectrum (carrier frequency), modulation (modulator amplitude), attack, decay, and volume (almost useless). Attack and decay usually adjust the envelope of the modulator. The sound from this is pretty nice. It's easy to get good sounds out of it without programming the endless parameters of 6-operator synths. There are also buttons for stereo symphonic, sustain (extended release), and vibrato (which acts as tremolo on some presets). The keyboard can be split to play bass and chords (optional) on the bottom part. There's a stupid auto-chord feature too, of course. And a "duet" button, which adds and extra note to whatever is played on the upper part of the keyboard based on the bass notes played (or something like that). Bass and chord sounds can't be edited, but there are 5 variations of each, selected from the "bass/chord voice" section.
The rhythms are actually pretty good, and somewhat editable. Using the "custom drummer" button, it's possible to select variations for each part of the pattern- base drum, snare, cymbal, and extra percussion. There are 5 variations for each. And there's the keyboard percussion switch, where the upper part of the keyboard triggers all of the drum sounds (18 lo-fi drum sounds, seems to be 6-voice polyphony). When a rhythm is playing, the bottom part of the keyboard can be used to play auto-accompanyment. There are 3 variations for the bass and chord patterns here.
All in all the settings are pretty versitile. Almost everything can be adjusted to some degree, and this tends to make things a lot more interesting than a lot of similar keyboards.
Inside, the CPU is an XA927B0 running at 3.58MHz. The FM sounds are generated by a YM3812 (OPL2), which was also used in Adlib soundcards. The drums come from a YM3301. Each chip has its own DAC- I don't know which one goes to which but one is a YM3012 and the other is a Y3014B. So it should be possible to install separate outputs for the drums and the FM sounds. The stereo symphonic circuit uses an MN3209 BBD chip and an an MN3102 driver chip. With a few modifications it should be easy to add controls for modulation speed and depth, and maybe an external input. Also, according to the site linked below, it's possible to add an 8-way DIP switch for more sounds. I'll probably do this one day.
PSS-570-1- cheesy demo, but it shows how good the deep bass sounds can be, and there's another one here.
Circuit bending info for OPL2-based keyboards: Fujitone 6A, MC-6
Yamaha has user manuals for nearly all of their products available here: Yamaha Manual Library (English)
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