One triode for parallel loop?

JJman

Member
Messages
994
I did some tinkering with the perfect-world no-buffer approach:

https://www.thegearpage.net/board/index.php?threads/453823

Definitely need at least a boost after the return. The approach “worked” but the wet path was too quiet as feared. Also confirmed the need for mixer resistor(s) before the final output to the PI. So I'm now ready and willing to add a tube but I'd like to try using only one triode at 1st. (This way I can also change the trem from one to 2 triodes.)

I'm working on a scheme but I'm wondering about the phase cancellation. The single triode in the loop will put it’s path out of phase with the dry path. Running a delay unit, where the unit is set for wet-only-output, I already know would not generate phase cancellation. However, with running a reverb "pedal" I'm not certain. My guess is that very wet settings on the reverb unit would not phase-cancel with the dry path, but full-wet settings may not sound good. Speculation at this point. :dunno I know I’d like to avoid the cancellation risk if easily done. Reverb and delay are the only affects I would need to use the loop for.

Is there a simple way to re-flip the phase in the loop? How do they do it in those A/B pedals that have the phase switch? Is it a small 1:1 audio transformer or something? Can it be done w/o a power supply for the flipping gizmo? SS blasphemy required? :Devil Tone destruction?
 

JJman

Member
Messages
994
Redman, please indulge me some more on this. Would I use the tranny to feed the plate of the loop-recovery tube, similar to a SE output? Or would I be employing it somewhere else? Would 1:1 be appropriate? DC ohms important?

It would not be a problem to spend some $ on a tranny if that solves the dilemma. This is my final build after all
icon12.gif
 

JJman

Member
Messages
994
Here's where I am so far.






Parallel.jpg



Can you tell I'm winging it? :messedup I would probably replace one or two pots with resistors once the workable settings were determined. I’m guessing on the transformer wiring and have no idea what the appropriate impedances and/or ratio would be.

The LTPI has 1megs on it’s grids, 470 on it’s cathode(s,) and 12k tail to 5k presence pot/resistor to ground. I’m thinking those numbers affect the appropriate tranny specs but I don’t know how to do the math. I’m still learning about load impedances and such.

Can this be done? Is there a tranny that might work? Maybe something small from mouser?
 

Fuchsaudio

Member
Messages
7,918
A true active buffered loop is unity gain and buffered on the send side, to drive long cables and low impedance solid state inputs on effects. The return side has gain, to compensate for the potentially lower signals coming back from a pedal or rack effect, and to match the return signal to the power amp. The loop is for matching, not so much boosting anything, when run correctly. They need not be tubes, although FET's and chips don;t sound as good as true tubes run at the proper voltages. Ideally you want the input to equal the output. With a few knob twists, you can get it easily.

There are no free lunches Gentlemen. Plug the wrong gear into a passive loop an hear tone-suck a la mode...

Simply buy something like a Verbrator and have a blast ! :) It's the simplest way to address these issues and has a great reverb built in too.
 




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