Yamaha SHS-10 (guitar style FM keyboard with MIDI- out)

The Yamaha PortaSound SHS-10 was one of the first portable FM keyboards with MIDI- out and a complex orchestrated accompaniment section ("style bank") with 25 styles those have each 3 fill-ins + ending.

The accompaniment can not be played in realtime the normal way together with the main voice by the lack of key split the left keyboard half can not be assigned to the accompaniment section. Instead there is a strange "melody on A.B.C." mode, which plays monophonic notes with the main voice but recognizes standard chords and plays them with the chord or accompaniment voice. In an other mode only chords can be played (annoyingly refuses to play any non- chords, much like Yamaha PSS-390) and chords can be also recorded into a simple internal sequencer, which holds 3 sequences. The preset rhythms are made from classic, very electronic sounding FM percussion (like known from old PC games on the historical AdLib soundcards). Also the main voice sounds are made from simple 2 operator FM. Interesting is that the SHS-10 has a pitchbend wheel and portamento with both adjustable intensity. This instrument was also released in a red case version and a few other colours.

regard: On eBay people sometimes pay now moon prices (200 US$ etc.) for the Yamaha SHS-10 those are very questionable. Despite this is a guitar- style keyboard with MIDI- out and pitchbend wheel, the keys are midsize and not velocity sensitive, the wheel has gritty resolution and the sounds are all very plain and simple 2 operator FM (like from old PC games on an AdLib sound card) with thin FM drums. Also the accompaniment styles are mainly centered on country musics, jazz, 1950th rock 'n roll and the like; many sound over- orchestrated and they are not really a proper choice for playing pop or tekkno musics. Regarding these crazy prices now paid for this rather simple sounding guitar keyboard, I regard it only a matter of time until people also decide to pay their ass off for the similar looking toy keyboard "RJP 896 Programmable Guitar Organ" ;-) (which has only 2 monophonic sounds and not even rhythm).

main features:




This instrument has a lot of controls and parameters. If you want to know details about the exact operation, it is a good idea to download the manual from Yamaha.

The preset sounds are made from very simple programmed 2 operator FM (without sophisticated envelope tricks) and don't sound really realistic. E.g. the "piano" and acoustic guitar timbres have the typical FM plastic guitar appeal with dull and hollow bass range. "synthesizer" is a thin and gritty synth brass "meow" sound (with that the instrument comes up after power-on - no good choice). The "rock guitar" is rather a nice sitar sound. The "marimba" has a strange dull plastic knock during attack of low notes. The "whistle" resembles an high pitch ocarina and makes strange aliasing distortions at high notes when transposed up. Select "melody on A.B.C." mode to play the main voice monophonic. Nice the the portamento feature (like with Casio SK-1), which makes theremin- like glide tones with adjustable speed.

The accompaniment styles have each 3 fill-ins and ending, but they are mainly centered on country musics, jazz, 1950th rock 'n' roll and the like and many sound over- orchestrated and thus are not really versatile. Instead of a normal chord section on keyboard, this instrument has the strange "melody on A.B.C." mode, which plays monophonic notes with the main voice but recognizes fingered standard chords and plays these with the chord or accompaniment voice. Variants of it are the "auto bass" and "auto chord" mode, those play only bass or only chord instead of the full accompaniment. The "auto bass chord" mode plays only fingered standard chords (no melody voice) but also ignores anything beyond establishment chords, which is quite annoying. Also the "single finger chord" plays only accompaniment on the entire keyboard. With rhythm off, the instrument plays manual chords instead of accompaniment; its preset sound depends on the selected rhythm number.

circuit bending details

FM synthesizer upgrade

The SHS-10 has only 25 built-in instrument sounds; this is a description how to cheaply add some more. The soundchip in my SHS-10 is an "YM2420, 79 04 72A". By soldering an 8x DIP switch into the traces to pin 2, 3, 4, 5, 6, 7, 10, 11 it gets possible to create many other strange sounds by opening one or more switches while selecting a sound and then closing them again. This kind of modification works also with many other FM keyboards, for details see here about my Fujitone 6A

Unfortunately the resulting sounds on my specimen are a little random (due to multiplexed lines and the timing of switching?), though multiple attempts are necessary to select a desired sound this way. (Previously selecting a sound with all switches closed makes it less random, but this works far from perfect. But at least for proudly sampling the sounds of the new and cheap "do-it-yourself DX7" it will do its job well enough. Possibly this flaw is only caused by missing pullup resistors at the sound chip input lines, which makes them respond on EM interferences.)

add 4 lower note keys

The keyboard matrix is active low, thus its inputs respond on GND. So far I remember well, the keyboard matrix on the keys PCB consists of multiple groups of each 6(?) keys. One group (the lowest notes) misses 4 keys and thus only has 2. To add 4 additional keys, wire for each of these missing keys a button switch in series with a diode in the same scheme like the other groups to activate them.

add locking switches & pedal jack

I wired each [a locking switch in series to a diode] parallel to the vibrato, portamento and sustain buttons and the 3 fill-in buttons to make them lock. Unfortunately by software reasons only 2 of these controls can be enabled simultaneously (likely because a matrix mess protection algorithm blocks further button presses in the originally diode- less keyboard matrix).

I also wired a 9 pin Atari style joystick port through two "4071" logics ICs (each containing 4 OR gates) with the vibrato, portamento and sustain buttons to enable to play these functions through an Amiga racing game pedal unit (which contains 3 foot switches). The OR gates simulate a button press in the key matrix when one input (with 4.7 kOhm pullup- resistor against +5V) is pulled against GND by the joystick and the other input by the corresponding key matrix output. The OR gate output is connected with the corresponding key matrix input line through a diode to pull it against GND when low. The diode prevents short circuit when the gate output is high.

(The OR gates make it possible to demultiplex a keyboard matrix place (that connects an input with an output line to trigger a function) into a DC controllable switch input. With an active- high keyboard matrix you would need AND gates instead of OR gates.)
Unfortunately the instrument is incapable to react on more than 2 of these buttons pressed simultaneously (despite my diodes), though only a combination of maximum 2 pressed pedals can be used at any time for playing the instrument.

Here you see the additional key buttons and the DIP switch block.

These are the lock switches for the effect buttons.

And here you see the Atari style joystick jack for the pedals.
Attention: I have only incomplete draft schematics of my modification, thus this description might be partly inaccurate or even wrong since it is based on them.

A bigger variant of this instrument was released as Yamaha SHS-200 (with 49 midsize keys and more preset sounds). The case design of the silver Yamaha SHS-10 was imitated in the toy keyboards RJP 896 Programmable Guitar Organ (only 2 monophonic sounds, pitchbend, vibrato, 10 demos, no rhythm) and RJP - Dynamic Keyboard MU-7986.

 removal of these screws voids warranty...    
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