Yamaha PSS-150

Yamaha PSS-150 (digital squarewave keyboard with programmable rhythm)

This simple Yamaha PortaSound beginners keyboard from 1985(?) has only 4 rhythms and 5 sounds, but features an interesting programmable drum pattern ("custom drummer"). The instrument has 4 note polyphonic squarewave sounds and a few interesting electronic percussion.

(photo from eBay, showing my specimen)

main features:

37 midsize keys
polyphony 4 notes (only 2 notes with accompaniment)
built-in speaker
5 preset sounds {organ, violin, vibraphone, piano, guitar} (selected in sequence by a single button)
4 preset rhythms {march, waltz, rock, swing} (selected in sequence by a single button)
main & rhythm volume sliders
tempo slider
single finger chord (only with accompaniment, no organ chord mode)
5 percussion sounds {base drum, tom, snare, open and closed hihat} of unique electronic style.

base & tom	= low & higher squarewave blips
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

programmable rhythm pattern ("custom drummer")
drumpad mode on highest 5 white keys
CPU "8530RX, 1G15030 251" (64 pins with strange zigzag layout), sound chip "Yamaha, YM2142, 57 09 82 C" (24 pin DIL)
sound generator is digital squarewave (same sound like "Yamaha YM2163" soundchip)
drums are digital squarewave {medium blip, low blip}, cymbal/ hihat = metallic digital waveform
demo button (Mozart serenade "Eine kleine Nachtmusik" ("A Little Night Music"))
alarm tone (2 note vibraphone "ding dong") warns to save batteries.
headphone and power supply jack

notes:

The sounds are selected in a sequence by pressing a single button multiple times. Rhythms are selected the same way; the rhythm select button also starts the rhythm. Unusual is that the instrument had despite this button saving concept a real analogue tempo slider. (The rhythm tempo can be set very low, but not extremely high.) This Yamaha instrument sounds very much like the Letron MC-3 and similar squarewave keyboards based on YM2163 soundchips, and like these it is only 4 note polyphonic, thus I guess that the YM2142 chip that is used here contains the same sound generator. The keys of the PSS-150 are held by a sheet metal frame with triangular metal leaf springs, which is quite unusual. According to an embossed stamp in the case it was likely made in the year 1986.

The main voice sounds are made from squarewave with different pulse widths and the envelopes have audible zipper noise. The "violin" features a delayed vibrato (a feature that none of my many YM2163 no-name instruments has) and also the vibraphone has a vibrato. Unfortunately the accompaniment tends to drown the main voice because it is a bit too loud and has no own volume control.

The drum pattern programming works here different from the "custom drummer" of the MC-3 and rather resembles the Elta KE-6. You have to select one of the preset rhythms as a template and press the "program" button which makes an empty rhythm repeats in a loop while a closed cymbal goes as a metronome (which is not recorded). Then you can now add additional percussion in realtime with the rightmost 5 white keyboard keys. (The pattern length depends on the selected rhythm.) You can delete the current pattern by pressing "program" again. The programming mode can in a limited way also be abused as a realtime tekkno drum computer and unlike the Elta KE-6 you can even play keyboard(!) during this on the remaining keys (with or without accompaniment). The pattern resolution depends on the selected rhythm and is high enough to get bizarre and complex "tribal" drum loops out of it. After finishing programming (press "stop"), the user pattern can be played by pressing "play". (The accompaniment of the user pattern can not be changed afterward, because starting the pattern with a different rhythm switches the accompaniment back to the one of the rhythm it was recorded with.) When "play" is pressed without recording (or after deleting) a user pattern, the instrument turns rhythm off and switches the rightmost keys into drumpad mode. Interesting is that although sound selection of this instrument is in no way OBS, you can play on the keyboard with rhythm and accompaniment, then program (and delete) in realtime a new user pattern and switch back and forward between the user and the default rhythm pattern all without stopping the accompaniment.

The nicely programmed polyphonic demo melody (which is even advertised on the box and gladly labelled on the case "programmed music") ignores manual sound/ rhythm switch attempts and does not even respond on moving the tempo slider.

A similar looking beige toy instrument with animal and voice samples was the 32 keys Yamaha PSS-110. A competitive product to the Yamaha PSS-150 was likely the Casio MT-36, which looks and sounds fairly similar.

*removal of these screws voids warranty...*

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