Hoffman AB763 Twin issues (cont from 2012)

[proaudioguy]

I went ahead and ditched both of the 220K mix resisters.  I've attached the Normal channel output to the vin channel output as discussed in the Dan Torres article.  No ill effects there,...or is that affects.  Anyway, it works.  I have all those articles stashed somewhere.  Its so hard to read them.  I am so much better with a schematic.  Perhaps I'll run across them at some point and now that I have a better understanding of what I'm looking at compared to 18 or so years ago, I might find some useful info.  That's if I can find them.

[proaudioguy]

https://www.youtube.com/watch?v=83l3rKw5zVE  2:30 in (there abouts) he cranks the reverb..... That's the sound I'm expecting to hear from my amp.

[proaudioguy]

I installed a post PI master volume using the circuit on page 193 of Weber's first book, which I purchased new when it came out.  Wish it had an index or table of contents.
I like it.  I will probably keep it.  At the moment the gigantic .1caps are floating off the 1 meg dual pot so I would not call it reliable.  It may benefit from being moved to the ground switch hole but it fits in the trem jack hole, which I don't use because I use a 1/4"TRS to switch trem and reverb.  I'm grounding it at the preamp ground bus.  I'm not sure if that is the right place.  I also used shielded cable (install mic cable).  Not sure if it needs to be shielded. but I figured it's signal and it's running about 6 inches each way.  The reason I mention all this is because the hum seems louder to me, but if I crank the input and turn down the MV then the hum is reduced dramatically.   The POT is grounded to the preamp ground bus, but mounted on the back of the amp.  Should I lift the ground from the back of the amp and just ground the signal to the preamp ground bus?  I think I have a ground loop through the pot casing.

[proaudioguy]

The reverb problem is fixed!!!

Princeton kit came in and I tried the reverb transformer in the twin. It worked so I mounted it and shortened the wires. The microphonics are gone, the feedback is gone.  The reverb is working as expected.  Not lush and phenominal sounding but I do not think that is unusual.  I can take it to 10 with a little hum/rizz coming up. Surf city!

My friend the tech told me day one to replace the tranny. He said let it hand and we if it improves but it didn't and being at the input of the reverb, but the microphonics being on the output, I could not connect the dots. Experience beat logic in this case.  He said "a bad reverb transformer will cause all kinds of weird issues."

I pulled the master volume back out.  It was a fun experiment.  Not needed for his amp.
My tech also told me attaching chan one to chan two together before the reverb without mix resisters was a bad idea.  I can find no where other than Torres and reference to Torres that say to do this.  Does it work?  Yes. But it sounds better when I pull chan 1 off.  I reinstalled the 220K resister before the PI (the original mix resisters). The gain was way too high and the tone too raw.  Pulling the channel one and that 220k opens it up a ton as it is.
So now that I have extra gain, but not too much extra at the PI, combined with the extra gain and tone by not using a bug based tremolo, I'm going to experiment with mix resisters at the connection point where Torres says to connect ch1 to get reverb on both channels.  Going to start with 100k-220k. Open to suggestions.

Once that is done I'd like to swap out cap values in the ch1 tone stack to be more tweed sounding.

Then I'll try the bias trem again.  I have the turrets and the tube socket so I might as well keep trying until I get it right.  Besides I changed (fixed) the bias circuit since pulling that out.  The tone is very close to what it was at its best only now I have a fully functioning reverb.