Yamaha PS-30, PS-20  (wonderful analogue keyboard with accompaniment & arpeggio)

These instruments from 1981 were the first portable fullsize instruments with versatile "auto bass chord" accompaniment and belong to the last analogue keyboards created by Yamaha. Technically they were the direct successors of the Yamaha PS-2 hardware and have nice analogue timbres, arpeggio and unusual analogue percussion.

Yamaha PS-30

(pictures taken from eBay)
Additionally to the normal (polyphonic) main voice, the PS-30 has a "solo" voice section that can layer the highest currently played note with an additional voice, that is produced by a more sophisticated monophonic sound generator. This solo voice employs a real analogue filter envelope and produces a wonderful analogue synthesizer timbre. Unfortunately this instrument seems to be very rare. An even rarer black version (seen on eBay) was released as Yamaha PS-30B.

main features:



This instrument sounds very much like an analogue 1970th home organ and seems to be based on similar analogue technology like the Yamaha PS-2. The built-in speaker is ok, although it is a bit small and has a noticeable mid-range resonance. The main volume slider can not mute the instrument entirely and its lowest setting is still a bit loud. Unusual is that this instrument has not only a cinch sound output but also an input jack.

In the case bottom is a groove to store a metal bow that can be used as a note stand. Like with the Bontempi Minstrel Beta, instead of a battery holder (mine is missing) a special power supply module PP-1 can be inserted into the battery compartment. Very bizarre is that the volume and tempo sliders work "wrongways", i.e. pushing them up makes sounds quieter or tempo slower, while pulling them down makes sounds louder and tempo faster. Likely sound mixers and graphic equalizers were so uncommon at that time that the control panel designers didn't come in mind to standardize this. Also the locking switches have an odd shape; they have a pivot at their rear end and tower up only with their front end when not pressed. I never saw such buttons at any other keyboard; possibly their design was inspired by piano keys. Also the golden "YAMAHA" logo at the front edge below the keyboard looks noble and piano- like.

The polyphonic "orchestra" preset sounds of the PS-30 feature many different vibratos; unlike with the Yamaha PS-2, the vibrato of "trumpet", "string" and "oboe" are delayed and fade in only after the sustain phase of the envelope begins, and even the accordion has a very shallow version of this vibrato. The "organ 2" has an undelayed medium speed vibrato, and the "vibraphone" has a rather strong and much slower vibrato. When a key is trilled with sustain, each new note occupies a new sound channel, which produces a great phasing sound and volume increase effect although this eats up polyphony. The sounds are based on squarewave tones with different pulse width, those are post- processed by different analogue filters, but unlike many early Casio keyboards with filtered squarewaves, the tones of this instrument are not just muffled duller but differ a lot in timbre, and regarding the technology they are even reasonable realistic. Only in the bass range many sounds turn into a more or less buzzy, sonorous purring drone, but this is a characteristic style element of squarewave based instruments. Such basses can resemble some of the famous POKEY sound effects on Atari XL homecomputers and are very different from the gradually duller and duller growing sine wave bass behaviour of average Yamaha FM keyboard sounds, but unlike e.g. Casio MT-60, the PS-30 features no really dry and creaky bass timbres but plays rather round and sonorous ones. Particularly the "organ 2" has a wonderful "black", droning squarewave bass, which is likely also enriched by the zipper noise of its digital vibrato. The "organ 1" sounds like a reed organ. The "trumpet" is duller(!) than "string" and should be better labelled "cello". The "piano" is a little dull and the "harpsichord" is harsh, a little thin and suffers from a slightly too slow attack rate which makes the envelope less credible. The "vibraphone" otherwise is a highlight of this instrument; it sounds great and (besides bass range) astonishingly realistic, although its sustain can not be turned off. The "oboe" sounds thin, but that is what it should. Also the "clarinet" is ok.

The "solo" preset sounds can be layered with the "orchestra" sounds. The solo sounds are only monophonic but include an analogue low- pass filter with decay envelope, which permits more realistic and expressive timbres. E.g. unlike above, the "trumpet" here really resembles what it was supposed to be. The trumpet and trombone fade duller and include delayed vibrato. Also both guitars fade duller; "guitar 1" is a dull one while "guitar 2" has a brighter timbre with some vibrato. The violin also employs delayed vibrato and sounds quite realistic. The saxophone has a mild, delayed vibrato. The "piccolo" is a sweet analogue tone with quite strong vibrato, that fades slightly duller; it doesn't sound really like a flute, but almost voice- like and resembles more a theremin or singing saw and gets a little brassy in the bass range; this cute and cheesy analogue timbre is definitely one of the great highlights of this instrument. The "funny" sound is a sort of e-bass with tuba timbre that fades brighter and has a strong vibrato. Interesting is that also in many early Casio keyboards (see Casio MT-60, CT-410V, MT-70, MT-30) sounds with "funny" in their name exist. The sustain button affects only the orchestra section but not the solo voice. There is a separate solo volume control and 2 "ensemble" switches to enable solo and/ or orchestra section separately. Unfortunately the solo section can not be used for a key split mode but only layered with the rest.

The analogue percussion sound a bit dull, but has an unusual timbre. The base is just a dull and quiet "pop" noise (like heard in the speaker when switching a radio on) consisting of 2 pulses muffled by a capacitor. The 2 tuned drums (tablas?, or congas??) have a strange timbre between drumming on empty plastic bottles and ceramic jugs. The hihat seems to based on a similar semi- digital technology like with the Yamaha PS-2 and sounds a bit more metallic than the analogue transistor noise ones found on other electronic percussion of that era. With the "8 bar variation" switch, an automatic fill- in is inserted every 8th bar of the rhythm; a manual "fill-in" button would have been much more useful. The default tempo settings of the individual rhythms seem to vary quite extreme (caused by different internal pattern resolution?). Likely to compensate this, the range of the tempo slider is quite wide, thus it needs to be tweaked with care because the tempo reacts audibly already on very small changes. In spite of this, the maximum tempo of some rhythms can not be set really high.

The "chord memory" switch makes simply that current chord is held after releasing the chord keys (this is no sequencer), but unusual is the way how rhythm and chord memory interact. The rhythm is activated here by 2 different locking switches; when only "start" is on, rhythm plays always and independent from the chord section. When also "synchro" is on, rhythm is started as soon a chord key is pressed, and then keeps playing until rhythm is switched off. But when only "synchro" and not "start" is on, then the rhythm pattern starts as soon any chord keys are pressed, and so far chord memory is off, the rhythm stops each time you release all chord keys; this permits interesting improvisations e.g. by trilling on chord keys. This odd mode I yet only found at a single other and also very old keyboard, namely my Bontempi Minstrel Beta. Unlike the latter, the chord memory here works only with the automatic accompaniment and not in organ chord mode (with rhythm stopped). In fingered chord mode the accompaniment plays the more notes the more keys are pressed, and this works even perfectly with all key combinations (up to 4 keys) and not just the few ones establishment has defined to be "chords", which permits very versatile accompaniment sound patterns. (This flexible behaviour is absolute no matter of course, see the later Yamaha PSS-390 for an annoyingly stubborn example.) The "multi bass" button changes the accompaniment; with most rhythms it makes a walking bass pattern. When no rhythm is selected, the instrument plays instead of accompaniment plain organ chords with a fixed timbre and a little sustain. The arpeggio has a decay envelope (like a harp) and the notes it plays change by the currently pressed accompaniment keys (but the count of notes stay the same). Its variation switch switches with most rhythms between a 16 step and an 8 step arpeggio pattern; only with "rhumba" it changes the speed.

circuit bending details

I haven't modified this instrument yet, but this is what I found out. The following descriptions relate to the instrument opened and placed keys facing down with view at PCB solder side. The bulky plastic case is mainly empty; there are only 4 small main PCBs in it those would likely also fit into an average PortaSound. In the middle is PCB 1 which contains the digital main components; they are the main CPU "YM1011" (IC1, labelled "key assign & rhythm"), the sound chip "YM1101 E" (IC2, labelled "tone generator"), the clock oscillator and some strange DAC hardware. Behind it is the vertical PCB 3, which contains sound preset switches , pots and helper circuits. To the right is PCB 2, which contains analogue filters for the main voice; behind it is the vertical PCB 4 which contains rhythm switches, pots and further helper circuits.

In the PS-30, to the left of these PCBs is the solo voice section which consists of PCB 5 and the vertical PCB 6. These PCBs are shielded at the keyboard side and partly on the back with aluminiumized cardboard to protect the sensitive analogue filter circuit against hum. Interesting is that the IC numbering on these PCBs restarts with "IC1", thus it was likely not included by Yamaha in the initial instrument design but came as a later addition to the finished hardware of the Yamaha PS-20. (The solo section is connected with the 10 pin connector "C3", which is only an unused solder pad row in my PS-20.)

Unlike the ancient Yamaha PS-2, the ICs in this instrument have no ceramic packages but are normal black plastic. But bizarre is that both large ICs are operated with negative(!) supply voltages; pin 1= GND, pin 39= -9V, pin 40= -4.5V, thus key matrix diodes against GND need to be installed "wrongways". Many functions (e.g. preset sounds) in the behaviour of this early analogue instrument are mainly controlled by the wiring of PCB traces and not hardcoded inside ICs, thus with some skill it can be likely upgraded to a versatile analogue synthesizer.

CPU YM1011

The YM1011 polls the keyboard matrix and outputs trigger pulses and digital waveforms for the percussion, those seem to have external envelope capacitors. Where present, the pin function names were taken from the writing on the PCB. (I haven't examined all of them.)
pin name comment
2 N2 connector C1
key matrix outputs
3 N3 ''
4 N4 ''
5 N5 ''
6 N6 ''
7 N7 ''
8 N1 ''
9 KC1 connector C3
(percussion trigger pulses?)
10 KC2 ''
11 KC3 ''
12 KC4 ''
13 B11 connector C2
key matrix inputs
14 B12 ''
15 B13 ''
16 B14 ''
17 B15 ''
18 B16 ''
19 B17 ''
20 B18 ''
21 (B19?) NC (higher note keys addable)
22 (B20?) NC
23 SY connector C3
24 ?  
25 IC connector C3
26 ?  
27 S. hihat percussion sound outputs
28 S. cowbell(?) ''
29 ?  
30 ?  
31 W. hihat percussion waveforms
32 W. snare ''
33 W. low drum ''
34 W. mid drum  ''
35 W. high drum ''
36 ?  
37 tempo in slide potentiometer
38 ?  
39 -9V supply voltage (measured ca. -8.5V)
40 -4.5V supply voltage (measured ca. -4.7V)

Pin 28 outputs a very clear and metallic cowbell clang, which seems to be used only as a component of the tabla(?) sounds although it sounds astonishingly realistic (may this have been Yamaha's first and unofficial use of an FM sound on a home keyboard?!?). The rhythm waveform outputs respond with continuous tones when connected through a resistor with GND(?); apparently these signals are sent through envelope capacitors.

tone generator YM1101 E

The sound chip YM1101 E outputs the squarewave accompaniment tones directly (using capacitor envelopes?), but the 8 note polyphonic main voice sounds are output through 4 lines as digital data and decoded by a strange kind of external DAC consisting of a few capacitors and IC6 and IC7; both are "Texas Instruments TL4558P, J104, LTJ" (8 pin DIL) and look like op-amps. The unusual thing is that they output 4 separate, polyphonic organ tones (labelled with the (organ pipe?) names {2', 4', 8', 16'}) those already contain digital envelopes (without vibrato & tremolo) and are mixed externally (apparently a kind of additive syntheses like in a drawbar organ) to form the final timbres (but there seem to be also capacitor filters). Connecting the data outputs directly with the amp produces no tones - likely the data have very high frequencies (the instrument makes no audible aliasing), although they may be simple bit streams decoded by op-amps and capacitors. So far I remember well, my Yamaha PS-2 has no external DAC and outputs squarewaves with 8 external envelope capacitors at its CPU.

It is difficult to figure out what this IC does in detail, but here is an incomplete pin assignment:
pin name comment
2 ? NC
3 ? NC
4 ?  
5 P. accomp. 1 accompaniment envelope trigger pulses
6 P. accomp. 2 ''
7 P. accomp. 3 ''
8 P. accomp. 4 ''
9 ?  
10 ? NC
11 ?  
12 ? NC
13 VIB vibraphone vibrato
14 DV  
15 ?  
16 ?  
17 ? NC
18 DAC data 1 digital encoded main voice
19 DAC data 2 ''
20 DAC data 3 ''
21 DAC data 4 ''
22 S. chord sound outputs
23 S. arpeggio ''
24 S. bass ''
25 ?  
26 ?  
27 ?  
28 ?  
29 ?  
30 P. percussion 1 percussion trigger pulses
31 P. percussion 2 ''
32 P. percussion 3 ''
33 P. percussion 4 ''
34 P. percussion 5 ''
35 P. percussion 6 ''
36 ?  
37 ?  
38 ?  
39 -9V supply voltage
40 -4.5V supply voltage

additional keys

12 additional high note keys can be added by connecting them through diodes from {N2..N7} at connector "C1" to CPU pin 21 and 22.

solo section

The pitch of the solo section can be tuned with the "solo tune" trimmer (which is also accessible through a covered bottom hole). Also the adjustable "master osc." coil changes the pitch. The trimmer "cutoff adj." likely sets the synthesizer filter cutoff frequency. (It is likely well replaceable with a real potentiometer.) 

synthesizer features

I haven't analysed this instrument closer yet, but the sound select buttons of this instrument seem to work very similar like the Yamaha PS-2 (see there) and thus can be likely modified similarly. Because IC6, IC7 output 4 separate organ drawbar tones, it is likely easy to add 4 potentiometers her to mix your own timbres. By adding a switch with a diode from GND to the VIB input (sound chip pin 13), the vibraphone vibrato can enabled with all sounds. This vibrato seems to contain even a mild chorus effect to enrich the timbre. As usual with analogue drums, the percussion looks also easy to modify. The  IC3 "1G02611" of the solo section is connected with multiple external capacitors and is labelled "VCF", which means likely "voltage controlled filter". The filter envelope reacts sensitive when the IC is touched by hand, thus it can be likely upgraded easily with additional pots to change the filter behaviour.

(Attention: I have neither modified nor fully analysed this instrument yet, thus I can not guarantee that the above instructions are correct. Especially the IC pin assignments may still contain some errors.)

Yamaha PS-20

This instrument is almost identical with the Yamaha PS-30 beside that it is missing the wonderful solo voice section of the latter; instead it has only the large brown logo "YAMAHA Automatic Bass Chord" there. In spite of this it is still a very nice instrument.
(picture taken from eBay, showing my specimen)

In my childhood my she- teacher owned this keyboard and she also took it with her into a hostel during a school travel where our class could play on it. As a little school boy with only a monophonic transistor toy organ, this fullsize instrument with its golden "YAMAHA" logo at the front appeared so huge and impressive to me like a concert grand piano, and it also became my 1st experience with arpeggios and automatic accompaniment. I first had bought a Yamaha PS-20 at eBay; the PS-30 seemed to be so unbelievable hard to find that it was fully out of reach and rather a "rumoured to exist" - not even Yamaha had listed it on their manual download site until I asked for it. My PS-30 has also the original brown imitation leather carry bag from Yamaha. The PS-20 seems to be much more common.
Such a dual colour button style on a beige case was also used on the Casio MT-60, although its controls are rounder. Model PS-20, SER. NO. 068209

(Caution: Both the Yamaha PS-20 and the PS-30 suffer of a really annoying disease; the foam rubber pods under their case dissolve into a tar- like, very sticky black goo. The only cure for this is to remove the black pulp from the pod holes at the bottom using a lot of Q-Tips and isopropanol (which still needs quite a lot of time), because otherwise it infests everything with black stains those at least on fabrics are almost impossible to remove. I had ruined a carpet floor with this stuff and could only get it out by rubbing it quite long with vegetable food oil and then removing this goo with concentrated liquid soap followed by plenty of water.)

A shorter 44 keys case variant of the PS-20 with only 6 sounds, 4 rhythms and far less features (no arpeggio...) was released as Yamaha PS-10, but this one is a totally different hardware class because it was instead just based on Yamaha PS-2 hardware. Already in 1982 Yamaha abandoned the analogue technology entirely and thus made all following keyboards only with strictly digital sound generation, while Casio kept analogue percussion and filters in their instruments far longer until the mid of 1980th. Nowadays the Yamaha PS-20 seems to be quite rare at eBay, and the PS-30 seems to be even extremely rare. Successors of these instruments were the Yamaha PS-55 (stereo) with the simplified variants PS-35 (stereo) and PS-25 (mono) from 1983, but these boring rectangular silver boxes with bulky speakers left and right to the keyboard were already digital (apparently based on Yamaha MK-100 hardware).

 removal of these screws voids warranty...    
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