Added the Active Effects Loop Circuitry tonight.

Last night I was able to get a rough prototype of an Active Effects Loop to function properly. It took all day to do it. Initially it didn't work, all I kept hearing was a loud tone shifting noise when I turned on the effects loop. I had to step away from it, and went to dinner. Upon my return I tried a few other things and finally was able to get it to work. Today I spent all day adding the circuit to the amp.

Here's an inside shot showing the added daughterboard with the effects loop stuff on it. I also was able to squeeze in a tube socket for the added 12au7 tube.


Here's the back panel. It will basically be totally removed from the amp until needed.
You then pull the Send Knob out. This adds the effect loop circuitry to the amp.
With the Send and Return volume knobs, you can then vary the input to the effects and vary the output from the effects back into the amp. I tested using a patch cord and It actually boosted the preamp output a little more than stock. It also gave the amp a little bit more crunch at max volume which was an unexpected side benefit. I've very happy with the end result as I was reading how a passive (with out an extra tube) effects loop cause a significant reduction in output. With the addition of another preamp tube we get the benefits of an effects loop without any loss in headroom.

Here's the 3 12ax7 preamp tubes with the added 12au7 Active Effects loop tube.