Big Briar etherwave CV, gate and pitch out mod.

[sean k]

I bought a populated etherwave board some years ago and considering I also have a Paia Fatman half finished it seems silly not to build the extra board for the etherwave so I can control the fatman. I've started drawing up the board from the schematic in the hot - rodding manual but need some info on the 1k 3% P.T.C. resistor and the 3046, 3086 monolithic pair.
I know the positive temperature co-efficient resistor and monlithic pair of transistors are used in analog synths in pitch to voltage creation to stop the transistors drifting as they heat up and cool down but I've never seen or used them so I'm looking for info to do the board. I suppose a place to supply them would be good as well.

Are the P.T.C. just like ordinary resistors with flying leads and does the 3046 monolithic pair come like a TLO72 with 4 pins down each side?

[Albert Kreuzer]

Hi Sean,

can't help you with a parts source in the US, but yes, PTC resistors come with flying leads (sometimes look more like ceramic disc caps), and no, CA3046 is not 8 pins but 14 (see attachment). CA3086 has the same pinout but slightly better specs.

Cheers,
Albert

[sean k]

Precision resistor is in Florida and they do a stock 1k for 4.50 and as for the 3086 and 3046 I think I'll just match up some 3906's. Music from outer space mentioned them as a substitute... I think. Any matched pair with an hfe about 300 should do the job. Thanks for the datasheet! I'll look on there for the individual transistor specs.

[Albert Kreuzer]

Yes, match them as close as possible and glue them together. It will be slightly less temperature-consistent, but probably good enough for this purpose.

Cheers,
Albert

[sean k]

Actually, it's npn's I'm after so they'll be 2N3904's and I'be been told I'm to match them base to emitter voltage drop which I've got a diagram of so thats what I'll do. Is there a specific type of glue thats best and while I'm thinking about it would it be advisable to then, once they are glued together, to wrap some aluminium around them as a heat sink?

[Albert Kreuzer]

IIRC there is a special thermo glue for this purpose, but I can't remember details. Anyway, I think superglue will be ok, and a common heatsink for both will improve the situation

Cheers,
Albert