Designing a Patchable Modular Synthesizer with Memory

Clive Jones CJones at
Wed Feb 21 21:42:00 CET 1996

Hi Chaps

I thought I'd share this with you. A couple of years ago I was pondering   
with the idea of designing a patchable analogue modular synthesizer which   
actually *remembered* were the patch leads were meant to be connected, I   
don't know whether this has actually ever been done. The idea was to use   
somebody else's VCO, VCF, LFO (etcetera) designs that were proven and   
thereby preventing me from all the design headaches and swatting over   
text books on oscillator and filter design techniques, and integrate them   
with a digital system for patch recall and pot scan. Each module would   
plug into a "backplane" that supplied power and the bus for the digital   
interface. Each module would be uniquely "coded" with a 5-bit binary   
ident number which the uP would recognise as being on the backplane -   
this meant that any module could be plugged into any position and   
detected by a regular or one-shot power up scan routine. Also the   
firmware would have images of each modules front panel layout of pots and   
switches, each module having an inbuilt 4x4 switch matrix (for an obvious   
maximum of 16 front panel switches per module) and pot-scan handled by a   
cheap ADC with 7 or 8 bit resolution - this would leave the uP to handle   
everything other than those tasks listed above. The uP would remember the   
patch lead settings by using a three pole jack socket that sent the host   
module ID number on *one* ring, and received the connected modules ID   
number on another - the third ring would be used for the analogue CV or   
Gate or audio signal (depending on it's use of course) but *only* after a   
handshake had been established between the two connected modules (they   
were talking to each other). Each jack socket would have an LED above it   
that would light when connection was established - the same LED would   
indicate that a connection was necessary if a patch was recalled from   
memory. The idea was that before recalling a patch the patch leads were   
removed, you then entered the patch number and the uP would flash the   
LED's above the sockets of the first two modules to be connected, when   
this was done the microprocessor stepped you through each individual   
patch connection until complete. I planned a small backlit LCD display as   
well which could be for programming information, and a neat little   
backlit keypad which would recall and one of the 100 programs I had   
planned for. The uP was going to be my pet favourite Rockwell 6502. It   
seems that as I have very little time on my hands nowadays to do such   
things so I hope that anyone wishing build a similar unit gets some ideas   
from this post - *except* greedheads hoping to make a quick buck that is!

Sorry no jokes this post chaps.


/<c.jones at> / ...and on the 8th day
/01344 850213 Work   / God made Synthesizers
/01344 850209/291 Fax/ ...and God was called
/01628 602106 Home   /   ' Tom Oberheim '

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