Hi everyone
I've been reading intensely here for a while but this is my first post. I have to say it's seems to be a great resource and populated by great people.
I'm hoping I might be able to get some thoughts from you guys on an issue that is coming up on the amp i'm currently building.
First I'll briefly describe the project, then detail the issue in question.
It's a DC30 circuit but with tremolo and the tube effects loop from 'The Ultimate Tone Vol.1' (titled 'The Best All-Tube Effects Loop'). I have a 3 position switch on the front which will allow Series, Parallel or OFF....totally switched out of the circuit at both ends and restoring the circuit to the normal non-loop configuration.
Each pair of EL84's has it's own standby switch and triode/pentode switch, so every combination is possible. There is no master volume.
The chasis is aluminium and the transformers are a pair of torroidals i had built to my spec's. I am using a choke and GZ34 rectifier tube. I will try to post a couple of pics as soon as i can work out how to do it.
Okay...now....here's the issue. I want to have both channels run through the effects loop. This will mean summing them just before the PI, the point where the loop is inserted. It looks like the simplest method will be take the signal from the EF86 channel volume pot wiper through a 220K resistor to the PI end of the 220K resistor in the TB channel heading into the PI. I wonder whether there will be loss of gain through the added 220K. I am also concerned about the 100K resistor to ground at that point, if i leave it in it could pull too much gain from the EF86 channel, if i remove it it might create too much gain from the TB channel. Any thoughts?
The second issue is the issue of phase. It looks to me like the 2 channels are out of phase, but as they normally feed each side of the PI, they will end up in phase at the output. If I sum the 2 channels , they will both feed one side of the PI and they will be out of phase, and i imagine will show up that way at the output. I had hoped to avoid that because sometimes it's great to play through both channels together. Basically i can't think of any way i can resolve this, it looks like if i want them in phase at the output, i'd have to run only 1 channel through the FX loop (no room now to install a second loop) and keep to the original 1 channel per input of the PI configuration , or, have the 2 channels through the loop and live with the fact that i have to have the channels out-of-phase.
I think the gain issue is more pressing at the moment.
Any thoughts or comments anyone?
(sorry for the long post, this stuff has been brewing in my tiny brain for a LONG time, hehe).
_________________ Lumbering dinosaur....what's a master volume?
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