I’ve been working on a guitar pedal. It’s a reverb and I’m attempting to add an overdrive stage into the reverb signal but it’s proving to be much more difficult than expected. For some reason when the drive potentiometer gets to a certain spot it seems to bring out a pre-delay before the reverb starts and the reverb drowns out the dry signal as well. Changing the diodes has improved the problem but more improvement is necessary. I’ve had to reduce the drive gain so much that the diodes are clipping fully due to the voltage not getting high enough. If I increase the gain any more, the pre-delay becomes very pronounced and too loud. I’m hoping that I can find another diode that has a lower forward voltage so that it begins clipping earlier and gives the desired overdrive without the delay. I haven’t been able to find a list of diodes and their corresponding forward voltages so I guess I’ll have to make one. I’ve noticed the Germanium diodes bias much lower and they also have a softer clipping which guitar tone aficionados prefer. I like the softer clipping because I’m not looking for hard distortion, just some edginess for the reverb.
Moving the clipping stage in front of the reverb unit and increasing the gain in front of the clipping stage seems to have given enough edge and gain for a satisfactory overdrive though the problem still arises when the drive pot is larger than about 15k Ohms.
Removed R6. I don’t see that it is necessary if R12 is there, although every other Belton brick circuit I’ve seen leaves it in there. Added R17 to keep the bypassed input from being sucked by the always-on output. I didn’t have the problem with the early iterations so I considered it solved and quit using the footswitch Now that I’ve put the switching back into the circuit there’s a massive drain. I’ve added another capacitor from the output to ground to cut high-frequency noise that was seeping through the wet signal. There’s still a trace of noise when I crank the gain on my amp but I’ve compared it to other reverbs (even a digital one) and I’m getting no more noise than those so I consider that solid. Another problem has arisen, and I think it has been there but not as prominently as now. I’m getting footswitch pop at the input. I know it’s at the input because it echoes in the wet signal. When I measure the input pin of the circuit while the input is bypassed, I’m getting over 2V. On the other side of my capacitor I get just over 4V, which is approximately the expected reference voltage being fed from Vref but the cap should be blocking all DC from coming back across. Turns out the cap was bad. Now all the DC is being blocked but still getting some switch pop that can be heard when the amp is cranked pretty hard. Hearing it pop when switching into and out of the circuit but it’s more noticeable when switching it on because I get an echo of the noise.
Made more changes. Added output buffer and removed R17.