I’ve posted about this before but have now 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 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. I posted an inquiry on diyaudio.com for guidance on using a transformer to flip the loop’s phase. My assumption was that I should use an “Interstage” tranny to drive the loop’s triode, and just switch the phase as one could on an output tranny’s speaker connections. However the specs were not good and the old impedance demon was rearing it’s head. Sy on the diyaudio board recommended that I use a 1:1 “input” transformer and the specs on the Jensen-brand units could not be better. Not cheap at about $65 but so be it. I wired it in to merely flip the phase before the grid of the loop’s triode.
Attached is the final schematic. At the full-dry blend setting there is some signal thru the loop which is fine. At full-loop setting the reverb is more than wet enough. At middle settings the full crunch 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-sequence has not been compromised. This is not a clone as the output is Tweed Deluxe and I have a PPIMV and output bias trem. Now with the loop I can finally have it all!
Should be able to record some tidbits tomorrow.
