MATRIXSYNTH: Sequential Circuits Pro One Circuit Board with Mushrooms, Shiva & CEM 3340, 3320 & 3310 Chips

Sunday, October 11, 2015

Sequential Circuits Pro One Circuit Board with Mushrooms, Shiva & CEM 3340, 3320 & 3310 Chips

Rev 1.2 circuit board via this auction

I've seen the mushrooms and Shiva before, but I do not recall the writing on the digital interface card before. Anyone know what it says?

"The CEM chips are as follows:

Three (3) CEM3340's, one each for the synthesizers two VCOs - Voltage Controlled Oscillators, with the third (white dot version) for the LFO - Low frequency Oscillator.

One (1) CEM3320 Voltage Controlled Filter. As installed in the Pro One this part is configured as a 24dB Low Pass Filter for that classic synth performance. However, the CEM3320 itself is far more versatile on its own. According to that data sheet it can be configured as a low pass, hi pass, band pass or all pass filter and it has voltage controlled resonance!

Two (2) CEM2210 Voltage Controlled Envelope Generators - VCADSR's. In the Pro One, one of these is used to modulate the VCF cutoff and the other controls that final output level from the Voltage Controlled Amplifier - VCA . By the way, the VCA is one-half of a CA3280 dual Operational Transconductance Amplifier, or OTA, while the other half of this device provides the glide/portamento function.

THE STORY BEHIND THE BOARD: I purchased the Pro One that this board was removed from several years ago here on eBay. The seller stated that he had no way to test it so it was being sold As-Is and that it may not work. He also stated that it has been stored in an unheated outdoor storage shed for a long time. Well, I bought it and guess what? It didn't work or at least it didn't work properly. During my initial testing I discovered that it would not read the keyboard, and you could not program the sequencer leading me to believe that the 8021 microcontroller was shot. I was able to verify that all of the CEM chips performed their intended function when I used an external source for the control voltage and gate except for the fact that the VCO's did not track at 1-volt per octave. Also, to the best of my ability to determine, all the switches, both slide and rotary, as well as all of the pots were working as they should. I later sold the chassis, keyboard and knobs to a friend and I kept the board intending to make a project out of it. I now realize that I never will get around to it and so it's time to let it go. It has been stored in an anti-static ESD safe bag since its removal from the chassis."

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