[sdiy] pre Uprocessor schematics with ADC/DAC?

thx1138 thx1138 at earthlink.net
Fri May 22 17:35:46 CEST 2009

On 5/21/09 1:37 PM, "Aaron Lanterman" <lanterma at ece.gatech.edu> wrote:

> The Synergy is a prime example - the digital oscillator board has
> about 120 standard TTL chips.
> You can find schematics/pics on my Synergy page.
> But really, all that is easier now with microprocessors or FPGAs.
> I think the Wave PPG had a lot of logic in the raw, but I'm not sure.
> Sent from my iPhone
> On May 21, 2009, at 9:28 AM, Dan Snazelle <subjectivity at hotmail.com>
> wrote:
>> this might be a strange request but i am very interested in ANY
>> information/links/ideas on finding old schematics from the 70's
>> (audio related but not just necessarily synth) that use Analog to
>> Digital Converters AND Digital To Analog converters but which use
>> logic instead of a microprocessor to control them.
>> all the synths i have looked at that have ADC/DAC setups have a
>> programmed brain of some kind controlling them (prophet 5, etc)
>> but i know there were some that used TTL or CMOS to send commands.
>> anyway....one particular example is the EVENTIDE H910.
>> i think i could learn some interesting things, such as how they got
>> the Audio In and Out, how they used multiplexers or sample and
>> holds, and also what types of clocks, and if they had presets,etc.
>> thanks!
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Hi Aaron and Dan,

This is a reply from Terry Shultz who worked at PPG from 1984-85 designing
and building PPG products in Hamburg.

The PPG system was build on the MCU6809 from Motorola. The EVU, Waveterm,
PRK, and PPG 2.2-2.3 were all 6809 based. The HDU was 68000 is I remember
correctly as was the Realizer which was MC68000 and TMS32010 DSP based.

We used the FLEX OS on the WaveTerm and may have been called UniFlex for the

The PPG Wave system used a few PAL's, TTL/CMOS Logic and SSM2044's for

Several implementations of this PPG system have been built into VST based
plug-ins and I have built a more advanced system for myself using DSP563xx
devices from Freescale.

Most people forget that many of these synth's were at best 12-bit systems
until recent history.

VC Clocks were built for modular synth applications while I worked at E-Mu
systems and were pretty good in those days.

At Oberheim in the middle 1970's we built the Poly keyboard controller from
discrete logic and used ready available CMOS devices. Our Dac's were
resistor Ladder based and were very good. It means you need to sort 100K 1%
resistors for even tighter matching. The TVS-2A and 4-8 Voice Modular were
all based on discrete d/a's.

If people are interested I am sure I can resurrect much of this older synth


thx1138 at earthlink.net

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