Yamaha PSS-80

Yamaha PSS-80 (squarewave keyboard with simple synthesizer & accompaniment)

This Yamaha PortaSound keyboard from 1989 is quite unique, because it combines coarse unfiltered digital squarewave sounds with a simple synthesizer (320 sound variations), reasonable polyphony and grainy electronic percussion.

(Photo taken from eBay; my specimen has no box.)

(Note: This keyboard sounds great, but don't buy one of these so far your only intention is to get a keyboard with faithfully imitated natural instrument sounds. Remember, this is a squarewave instrument and though many of its sounds sound not even remotely like what is written on its buttons, though bought with wrong expectation it may disappoint you.)

main features:

32 midsize keys
polyphony 6 notes (only 2 with accompaniment)
built-in thin sounding speaker
8 OBS preset sounds {clarinet, trumpet, piano, accordion, vibraphone, rock guitar, mandolin, fantasy}
8 OBS preset rhythms with interesting percussion {8 beat, 16 beat, tango, samba, swing, march, 12 beat, waltz}
tempo +/- buttons (16 steps)
volume control (4 steps, reduces bit resolution badly)
simple synthesizer ("voice variator" buttons {bright, mellow, short, long} => 8 timbres + per preset sound 5 envelopes permit 320 voice variations)
single finger chord (only with accompaniment, no organ chord mode)
simple sequencer (monophonic record & playback, no edit, but it can be played live to it)
sound generator is multipulse squarewave. The digital envelopes (with audible zipper noise) are linear and thus sounds unrealistic because they fade silent too soon.
drums are digital squarewave:

base & tom	= very low & slightly higher (squarewave?) pop noise
snare	= shift register noise
open cymbal	= unique electronic metallic timbre (low- res waveform sample??, or 2 mixed squarewaves?) with truncated decay and audible end click.
closed cym.	= dto. with shorter envelope

sound generator is digital squarewave (crystal clocked)
CPU="Yamaha XF7780, 35V0B78P, 9F3" (40 pin DIL), additional IC "YM3427, 96 09 67 F" (16 pin DIL)
demo button (short pop music monoto, cycles through all sounds & rhythms)
power supply jack

notes:

Like with Yamaha PSS-20, the volume control of this instrument steals bit resolution from the sound, which dramatically truncates some envelopes and thus even turns some sustaining tones into short blips because only the attack and decay phase stay audible at low volume setting. Thus it is strictly recommended to add a real potentiometer for volume control and treat these buttons rather as an additional envelope control feature. Also a sound output jack needs to be added for reasonable use. An even greater variant of the PSS-80 (that includes the same sounds) is the Yamaha PSS-100.

The sounds are digital multipulse squarewave with audible zipper noise (similar like the Letron/ MC-3). The "piano" ignores key press duration. The "trumpet" starts with a strange smack, has a fast and strong vibrato and its harsh timbre is at least slightly more natural than trumpets on other squarewave instruments. The "vibraphone" has a slow tremolo with such a high amplitude, that with most volume and envelope settings it completely mutes the tone in the quieter phase. The "rock guitar" is rather a thin and harsh organ tone that starts with a click and resembles bagpipes timbre. The "mandolin" rings fast. The "fantasy" is a sort of slower ringing mandolin which fades silent.

The "voice variator" synthesizer buttons {bright, mellow} change the pulse patterns of the square wave in 8 steps and thus permit to select any of the 8 existing timbres for the sounds. The {short, long} buttons permit to select among 5 different preset envelopes for each preset sound. Unlike the timbres, the 5 envelopes differ among the preset sounds, thus every sound has an own set of 5 envelopes. The longest envelope typically softens also the attack phase while the shortest envelopes reduce not only the decay phase but also the sustain level (with "fantasy" this disables ringing). The {bright, mellow} buttons also change the timbre of still held notes, while {short, long} only affect new pressed keys. Selecting a preset sound always mutes held notes and resets "voice variator" values to defaults. All button presses on the soft touch panel cause a blip sound, which limits their use as a realtime sound control.

The cymbal consist of a metallic digital waveform, similar like MC-3 cymbals. The base and tom drum are a very low and a slightly higher short popping noise. The "16 beat" rhythm has an accent on the cymbal and "tango" features a drumroll. Rhythms can not be switched immediately but always wait until the pattern ends. The single finger accompaniment plays only 3 standard chords. The sequencer can be used to playback a monophonic voice while playing to it. (Rhythm does not reduce polyphony, but sequencer playback always starts the rhythm it was recorded with. The sequencer can not be used without rhythm, and always plays with the sound that was selected first during recording. The accompaniment is not recorded.)

circuit bending details

Aaron Howald e-mailed me the following info:

"I got a damaged Yamaha PSS-80 as my 3rd bend attempt nearly 2 years ago. I found that the key press beep CAN be disabled! It comes from the CPU, at pin 5 (I just cut the line) also try playing with switching the 4 data lines in/out between the CPU and sound generator - you can get weird beats, alternate keys sounding different, etc..."

Attention: I haven't verified this info yet.

A quite similar but simpler Yamaha squarewave instrument (no synth, no accompaniment) is the small Yamaha PSS-30. An even greater and more advanced variant of the PSS-80 was released as Yamaha PSS-100 (same case, each 16 sounds & rhythms, better sequencer, no OBS buttons).

*removal of these screws voids warranty...*

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