REI <==> Reverse Engineering, Inc.

Old Crow's Synth Shop -- The yamaha CS-50

The CS-50

Although the CS-80 is in a class by itself, this does not mean the CS-50 and 60 aren't quality instruments. In fact, some things are better done on a CS-50 than the 80 simply due to the fell of the keyboard action. The CS-80 has the ideal touch for those who prefer the piano, but the CS-50 and to a lesser degree the CS-60--I say lesser because the action is longer and thus a little less crisp due to the extra mass--are very good at sharp attack-style notes and chords--something that just can't be done on a weight keyboard.

Part of this is based on the fact the aftertouch, though monophonic, is not based on force sensing resistors but instead on a light source and photoresistor. The photoresistor alone has "fast to lose resistance, slow regain resistance" that imparts a sort of fixed attack-release that sound very nice as part of a pizzacato or staccato playing style for a given phrase. On the CS-50, with the lower-inertia 49-note keyboard, for a composer this is a very useful tool.

Since the CS-50 shares the exact same voice cards (save for some resistor values changed to select octaves differently than the '80), any sound is directly transferrable from one channel of the CS-80 to the CS-50 or CS-60. Since all three machines have the exact same ring modulator and controls, the same "breath phrasing" can be applied. Vangelis is a master of this technique.

Restoring a Trashed CS-50

I bought this machine originally for use as spare parts for my CS-80, but after reading Juergen Haible's account of the aftertouch feel of his CS-50 and experimenting with some lead-type sounds, I decided that the machine should live its own life. The problem is that the my CS-50 got so manhandled by a popular parcel shipping service (UPS) that considerable internal damage was done. When I opened the shipping carton and an electrolytic cap fell out, right away I knew something was not right. Even so, I set out to repair the beast...

The 10kg power supply was sheared loose and went on a rampage inside the case.

Note the front panel slider potentiometers that were POUNDED FLAT!

Bad power supply, Bad!

Multiple compound PC board fractures, this PC board is finished.

Service manual pictorial of VSU board artwork.

My version of the PCB layout and circuit trace artwork.

I made the new board in a local circuit board etching lab, salvaged some parts from the broken board, and constructed the new one. It works fine, even if the layout is a little different due to what parts I had on hand formfactor-wise versus what was originally used.

Update: Repairs

New linear potentiometers installed and wired.

Rebuilt and remounted power supply.

Replaced some 4000-series CMOS chips on the KAS and SH boards. Tunes up much better now.

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Scott Rider --