George Dennis Parametric Wah + Vol

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George Dennis Parametric Wah + Vol

Postby KippeKiller » 25 Mar 2018, 15:10

Hello,

i currently obtained a George Dennis Parametric Wah Volume Pedal, i guess it's the GD65.
It has some issues with crackling in the Volume Mode, i did not solve it yet.
I have not found anything to help me finding the culprit so i started tracing the unit myself.
The gut shots are attached and the first tracings of the signal path. I left out the switching part and the led drivers.

The circuit is somehow different than the others GD wahs i had or found schematics of.
The Wah circuit consists of a TL074 for and a ML5207, this part works fine.

The CV for the ML5207 is generated with a TL064 which is also used for the Volume circuit, as far as i understood the ML5207 is not used for the Volume.

I used different colors

Yellow is the signal path
Black is Ground
Green is the virtual ground
Light Blue is a Voltage generated via two resistors and a TL431 in between (bottom right corner)
The rest is red as of now

Maybe anyone has an idea where the crackling could come from or has fun looking at the pictures.
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modman (29 Mar 2018, 15:16)
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Re: George Dennis Parametric Wah + Vol

Postby lars-musik » 29 Mar 2018, 16:48

I once had to repair a George Dennis wah (the normal orange one). I wrote an email to them and had schematic and layout in my mail the same day. Maybe there is no need to trace that.
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Re: George Dennis Parametric Wah + Vol

Postby KippeKiller » 30 Mar 2018, 17:09

I might consider that, but it's somehow fun to get to the bottom of that circuit.
Considering the static noise i had no luck so far. Changed all the bipolar caps, no luck. Changed the opamps, no luck. Took out the TL431 and fed the 2,7 Volts externally, no luck.

Is it possible for the LDRs to go bad and cause the static noise? because it comes somehow from that area.

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modman (25 Apr 2018, 15:03)
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Re: George Dennis Parametric Wah + Vol

Postby KippeKiller » 05 Apr 2018, 23:38

I got the Schematic.
Just in case someone needs it George Dennis still has it, or i do.
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