David's polymoog restoration (video# 1)

Hello everyone, this is a video of David Koltai's polymoog.

[synthpro]

Unfortunately, I have never had any luck finding a datasheet for the E402.

The part # that i have used is a 2N3954 along with the NTE461 which also seems to work very well.

I have never worked on a memorymoog but do know that it uses a digital computer to control Curtis Oscillators but the VCF section is the moog ladder filter and I am guessing that the Moog Source filter setup is very close to the memorymoog.

Hope this helps,
Jareth

[skyprop]

Damn! You Know your Stuff!!!! I know who to contact if any of my vintage Synths need Serviced. At the moment I have a Moog Source and a Roland Juno 6

[tinkerwithstuff]

Maybe you can use them where you'd have to, cheaper than 402, e.g. 3 bucks for 20pcs on e*ay.
Then glue them together with thermal conductive glue on the flat sides, I've heard good things about this method for 2-transistor expo converters.

I didn't pick them randomly, the J111 was suggested in a siliconix(?) appnote for JFET attenuator circuits (which I initially tried to use to make VC-able feedback, not too satisfactorily), so I figured they may be usable for audio, not just as switches.

[synthpro]

I will get that part # for you. I have used a few different duel N channel JFET's which is what the original E402 was. I do have some new old stock E402's but I try to only use them when needed, hard to get and not a cheap part at that.

Will be in touch,
Jareth

[tinkerwithstuff]

Anyway, if you have datasheet for the 402 (couldnt find it), compare it to J111, 112, 113, if one of them's close enough to 402 . The pure filter, w/o resonance, sounded just like the version w/o the JFETs ( & manual emphasis only) I had before, so it seems the J113s I used did the job, just don't know if it will survive all conditions possible in the circuit. The 111, 2, 3 all have slightly different on-resistance & currents.

[tinkerwithstuff]

Could it be that you mentioned the memorymoog in one of your recent videos, if so, you may have helped me already :-D
Whan waking up I was thinking of that thing, never looked at its schematics, but since I thought a thing callled "memory", it surely must save patches and needs CV for emphasis, and voila - it has, and uses op-amps instead the JFETs...
I think I'll try that one out.

[lesingemonotone]

the caps you're refering to at 1.18 is C46 and C47 (10uf) right? I have to change these in my 203a, thanks for the reminder!

[tinkerwithstuff]

Hey! You mentioned JFETs on the filter having been replaced by more modern components.
Could you elaborate? Is the use of JFET similar to Source?
I recently became a electronis dilettant & synth fan :-D Wanted a moog filter, looked at the moog Source VCF for it has voltage control of emphasis, but uses old JFETs.
Managed to get it sort of working with two J111 which are not the most frequenly found parts either, though (wouldn't call it success since the resonance is not yet working properly)