Poly synth (string synth focus)

whomper · Last edited by whomper on Thu Dec 24, 2009 9:52 am; edited 1 time in total

Hi,

Recently I have been thinking of perhaps going on to build a poly synth. I am not too keen on complex features, like memory etc.

I am thinking about: 6 VCO, 6 ADSR, 6 VCA, 1/2 filters + ADSR, 1 LFO.

The main orientation would be pads and strings, so I might include a JH Solina Ensemble Chorus.

I am wondering whether there are PCBs for the VCO/VCA/ADSR combinations so that I can save $$$ and space.

Alternatively, which PCBs would be cost effective?

Any feedback would be greatly appreciated.

(Apart from builder's joy, I am going DIY here as buying an analog poly synth would trigger a home alert, vs. bringing it home in parts and pieces Smile

)

emdot_ambient · Joined: Nov 22, 2009 Posts: 667 Location: Frederick, MD

You should come up with a DIY divide down string synth like the Solina instead Very Happy

magman · Joined: Feb 04, 2009 Posts: 363 Location: Liverpool, UK

There were quite a few Polysynth designs published in magazines in the late 70's and 80's but they were either op-amp and discrete based or CEM based, so you aren't likely to find anything of interest in these old designs, apart from the key assignment matrices.

As a first port of call for more modern designs, I would have a look at the modules that George Hearn has built (he has built himself a Polysynth from these modules), here:

http://sites.google.com/site/hearnmorley/

Even with these modules, you are potential going to have in the region of 100 control pots, or you are going to have to build something computer control with Sample and Hold chips, like the CEM5510 (along with a suitable D/A convertor).

Other things to consider are the PIC based Synth chips that Electric Druid has developed, here:

http://www.electricdruid.net/forums.html?page=projects

Last but no means least, I have to ask the basic question, do you definately want to go analogue or should you be looking at some digital options as well. There are quite a few good AVR and Arduino based designs on the web that may be a much cheaper solution.

Good hunting

Magman

whomper · Posted: Thu Dec 24, 2009 10:32 am Post subject:

whomper · Posted: Thu Dec 24, 2009 10:37 am Post subject:

magman · Joined: Feb 04, 2009 Posts: 363 Location: Liverpool, UK

If you're going down the strictly analogue route for the synth part (you will almost certainly have to go the digital or MIDI route for the keyboard control and Key assignment), then effectively you are supplying a CV to the control inputs, so I suspect you will have to have some form of buffering for the CV's or the different modules will cause you all kinds of problems.

It might also be worth looking at some of the Oberheim designs, as they typically use voice cards that a computer controlled. The voice cards are often CEM based, so very difficult to replicate now, but an OBmx type design with a more modern voice card would be very interesting, especially with all of the modulation routing options that some of these Oberheim designs are famous for.

Regards

Magman

emdot_ambient · Joined: Nov 22, 2009 Posts: 667 Location: Frederick, MD

Another way of going about it is to look for things like Doepfer's A-190-3 Polyphonic Midi-to-CV/Gate Interface (not released yet). Where one MIDI input splits out to control multiple voices of monophonic modules.

The down side, of course is that each voice must be programmed independently. The up side is that each voice can be programmed independently, much like a lot of the early Oberheim synths could.

MOTM's 650 MIDI converter can handle 4-voice allocation as well.

emdot_ambient · Joined: Nov 22, 2009 Posts: 667 Location: Frederick, MD

Tim Servo · Posted: Thu Dec 24, 2009 4:04 pm Post subject:

As I recall, someone on AH or SDIY was working on a CPLD version of a top-octave divider. They had run into some snags, so I don't think the project is finished. This is one of those things that sounds simple (high-frequency clock in -> a bunch of dividers - > an octave of equally tempered square waves out), but really becomes difficult when you get down to actually implementing the thing. Also, there's a lot of repitition in a divide-down based synth. Look inside an ARP Omni someday if you ever get the chance; simple circuits, but LOTs of them.

Maybe a (relatively) simple way to do an analog poly would be to buy two or more simple synths like the PAiA Fatman. They're about $200 each, and you could just buy one at a time and put them together. They already have a built-in MIDI converter, although I'm not quite sure how a polyphonic setup would be pulled off (put each on on a different MIDI channel, and then get a controller that can output a rolling MIDI channel assign for note and velocity messages?). Too bad the Fatman doesn't have a "chain" mode like the Dave Smith Evolver line. Otherwise, maybe something like a set of ASM-2 cards?

Tim (relatively simple) Servo