Guitar amp effects loop finally done.
Thanx to Sy for steering me to use an input tranny for my guitar amp enhancement project. Original thread:
Phase flip needed -Interstage Transformer?
It’s a parallel effects loop. I wanted to be able to use reverb and/or delay but running either before the main input doesn’t work correctly when cranking this amp. This because the 3rd preamp stage clips and compresses when cranked (as it should) resulting in the reverb/delay portion of the sound being “blocked” in a nasty way. Now I finally put it all together. (Being out of work frees up plenty of time for these things
I was committed to using only one tube stage for the loop and wanted to re-flip the phase in the loop so there is zero risk of it phase-canceling with the base/dry signal. Using a resistor and a pot I determined the correct voltage divider setup to tap some signal off the output of the 3rd preamp stage. My table-top reverb unit has a “line level” mode with a clip indicator light so I set the “send” strength to the loop to be just below the point that clips the effect unit when cranked. I then replace them with resistors to match the setting.
Attached is the final schematic for the loop. At the full-dry blend setting there is also some signal thru the loop which is fine. At full-loop setting the reverb is more than “wet” enough. At middle settings the full (good) distortion and compression of the amp is intact along with the added reverb from the parallel loop. I verified that the various stages in the amp are still clipping in there proper sequence so that “mojo” has not been compromised.
Thanx again !