DOD G7, different versions

[Reidk]

Hey all. A voice from the old Ampage days here. (Search the archive for "Reid")

I'm trying to fix a DOD G7 rack unit ("Guitar FX Processor/Preamp"). I have a schematic, but it seems to be for a very different version. The schematic says "05-6016 Rev A0". The board I have says "05-6216 Rev A". There seem to be quite a few differences (not the least of which is that the schematic shows a -5V supply that does not exist in my hardware). My unit also has LM353 opamps, while the schem calls out NJM4560s. Lots of other diffs, too, although it seems to be the same product.

I got the "wrong" schematic from DOD support, and I'm waiting to hear back from them if they have any others. In the meantime, can anyone offer any help? Maybe at least a source for obscure DOD schems? The G7 seems to be The DOD Product that Time Forgot.. It's not mentioned anywhere on the DOD "discontinued products" support page.

The symptom is no output with the noise gate active. With the gate bypassed, if I crank up the level I can hear the input signal very faintly along with a lot of hiss. The odd thing is that the input signal seems to be intact through the first few input stages, past the point where the schem says the gate sense is taken, so I don't know why the gate is shutting it down. I'm wondering if the gate sense is really taken somewhere else in my version.

Thanks for any help.

Reid

[Enzo]

LF353 -- 4560... both are dual op amps and are more or less interchangable. In fact I just installed a 4560 in place of a LF353 last night in a GK amp. Works fine.

Look at your old schematic. What in there uses that -5v? What now does that same job in your newer product? Without looking, I'd be betting the -5 was part of some FX circuit, maybe a chorusing circuit.

Otherwise is there great similarity? Enough to steer you through?

And do give them a chance to correct their oversight. You told them your board number, right?

[Reidk]

Enzo, thanks for replying.

I know the op-amps are interchangeable. I just gave that as an example of the diffs in case it rang a bell with anyone.

The -5 supply in the schem is used all over the place. The opamp chips, for example, are shown with +5/-5 supplies in the schem. On my board, they're at +9/0, with 4.5 V bias on the inputs and outputs.

The circuits are similar enough that I can get by, and I did give DOD my board number and am awaiting a reply.

Thanks again.

Reid