Greetings,
I have seen this issue mentioned here and there, but never any full resolution on is it normal.
On the bench I have a GP-1 unit with the following test conditions:
Input: 100mV RMS into hi-gain jack @1kHz
Tone controls at midpoint
Bright & Deep switches normal
Gain control 0
Reverb, phasor, rate at zero
Master volume: 10
Output: 8 ohm dummy load
With the gain control at zero, I get 8V pk-pk at the output. As I rotate the gain control, there is essentially no change in amplitude until the knob gets to 7, and the amp goes from 8V to clipping in the last 2.5 ticks of the gain control. That makes for a very touchy gain control. Is that normal? By the number of mentions it seems normal, but I certainly don't like it. It has a 1M log pot. The amp had a wire hastily tacked onto the open lug of the gain control pot and connecting to the ground lug on the treble pot, which I removed.
As far as I can tell the amp is working as designed, but yowsa. Just looking for a sanity check here. Thanks!
Reverse Log Taper?
The later schematics (GP3 &3A) use Reverse Audio Taper pots for Gain Control. Maybe the "behavioral feature" you found was the reason for the change. Just a guess..... -mgriffin
It's by design
It's not a great design necessarily, but I think that's how it was supposed to work with the components in the design. As noted, later designs of both RD and RP 2165/2100 used RA taper pots for the gain. The RA taper was used in the earliest RD design for the hot channel. The later RD-50 (1650-RD) design uses regular Audio taper but here the pot is the feedback resistor, not the input resistor. In the RD/RP 2165/00 amps with the original Audio taper pot in the gain control you have to be quite generous with the gain pot - it can not be treated as the channel volume in the older 2 channel design.
Cheers,
Lars