Yet one more George Dennis Volume Pedal thread...


Just got a GD20 (mono) pedal today from eBay. I plugged it in, and was not too excited; the sweep was very smooth, but I lost the punch when it was hooked up. So, I went back and forth between it plugged in and it bypassed to see what it was that it was missing. It seemed deceptively simple -- it just didn't have quite enough volume on full forward. So, I opened it up and traced the circuit out.

For anyone who cares, the components are pretty good. The dual opamp is a very high-quality one, not your run of the mill 4558. There is a 4.7K resistor in the feedback loop of the first opamp that sets the initial gain, and the second opamp is set for unity. I simply swapped out the 4.7K resistor for a 10K resistor, and, if anything, I have just a touch of boost. I would ballpark a 7.5K to 8.2K for complete unity. It's got beef, punch, sparkle, and sounds great overall.

A simple little mod, but well worth it. The pedal action on this thing is great, I like the size, and the construction is very nice. It just needed a little bit more oomph. My guess is that it was set with a signal generator rather than a guitar pickup.

Oh, and the trimpot has little to do with the gain, as internet legend professes. I figured that since they are in Czechoslavakia (OK, my spelling failed me), they might be tough to get customer support, and there weren't any schematics on the internet. It's just a straight-ahead dual opamp buffer/volume circuit with the photoresistors between the two opamps.

If you've got one and don't like the "tone-sucking", as people call it, this helps it out mightily. I didn't think of it as sucking tone, just not enough output to be where it needs to be. Personally, I'd rather just add a resistor to the feedback loop of the second opamp, but the circuit traces make that one kinda difficult.

Good pedal, great price, good stuff.


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