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Old 01-27-2013, 11:08 PM
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Synthetech Synthetech is offline
Join Date: May 2012
Location: USA
Posts: 711
Default DW8000 filter PCB repurposing help (klm 662)

OK.. time to pick some brains on an idea I have.

I have a DW8000 filter board.

I'm trying to understand how the board works.. how Korg applied it to the voices
and try reuse it as an external FX somehow..

Schematics are here-


pg. 19

It has 8 of the NJM2069 analog filter chips (same as the one inside the Korg Poly 800)

It appears to have a 74138 driven by the '175s FF's (used as a buffer?) to select which channels the 4066 bilateral switches
will be on or off to pass Sig1 and Sig2?
I can see 1 sig comes in on connector 12B/pin7 and is called "H"
What is Pin 6 for? A select line for the 74138 to use?
Are both Sig1 and Sig2 the same?? From "H" and being split to them?

Going over to connector 13B, I find we have 3 4051 1-of-8 switches.
FCV goes into IC2/Pin3
CV goes to IC1 and IC3 @Pin3 on both.
Q1-3 are used to create a 3bit word to select which output line on the 4051's
will pass the Pin3 signal onto the quad op amps..
Q3-5 are select lines.. to choose which 4051 is active/using the 3bit data word.

IC8 looks like it controls Signal levels for Sig1&2, the Resonance Level and
Noise Level.

IC5 looks like it's a modulation control.. I've got a bit lost as to what MG.CV
"D" and D. Time "E" do..
"D" goes to connector 13B/Pin9
"E" goes to 19A/Pin6

It appears the noise source is on this board, but not the actual waveforms for
tones. Tones apparently originate from a DAC on another board.

From the looks of the traces, it seems that all filters are modulated the same way.. all 8 at the same time.
I thought the DW8000 might make each filter modulate differently/independent of each other...

I was under the impression it would use two different tone signals and one extra
for the noise at each filter.. but it looks like only one signal comes into the
entire board at connector 12B/pin7.

Each of the 8 "voices" has their own group of trim pots to control VCA, VCF Lin,
VCF Log, Reso and Sig2 Level (Level 2).

It seems that this relies alot on digital signals to quickly change the mix of
actual audible signals, plus distribute CV values amongst the OP AMPs.. so the
filters will be modulated.

Did one of the 74138s chop up a multiplexed audio signal and divvy it out to
each filter?

I'm just curious if there's a way to bring a signal into the board and for
simplicity, use each group of pots to tweak the filters open/close/resonance..
maybe even use the Noise in there...
Perhaps patch one filter's out to another filters's IN..

and just how would I go about creating a LFO modulator?

And of course somehow utilize the -12d filter output (not even hooked up on this

If anyone cares to take a journey into this beast, I'd love to hear opinions..
I've spent most my Sunday morning tracking down traces/components to get a grip
on how I can repurpose this for some kind of custom filter bank.
I only have seven of the filter chips left.. I sold the eighth one. I might
keep the seventh and try to use just 6 or less on this board if I can find a
good way to utilize it.

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