One triode for parallel loop?

[JJman]

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

http://www.thegearpage.net/board/showthread.php?t=453823 (http://www.thegearpage.net/board/showthread.php?t=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?

[donnyjaguar]

Short answer, there's no easy fix. Longer answer, it depends on the amplifier. :)

[Structo]

Perhaps the Dumbleator is the answer to your quest?

[RedMan]

If youre willing to cough up the bucks for a transfomer that's all you need really. That will give you phase reversal and high impedance gain. I'm guessing the PI has a fairly high impedance input.

[JJman]

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 http://www.thegearpage.net/board/images/icons/icon12.gif

[JJman]

Here's where I am so far.






http://home.comcast.net/~jjsant3250/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?

[RedMan]

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 http://www.thegearpage.net/board/images/icons/icon12.gif

What I was thinking is to use a step up transfomer instead of a triode for recovery, then you wouldn't need an extra tube, hole, power req. etc. and you would have the ability to reverse phase easily. You would end up with a pretty high impedance out of the transformer and it could vary quite a bit depending on what was feeding the return jack but you could match it to a high impedance grid without a grid resistor, just running the secondary for the grid to ground reference. Then just a phase reversal switch in between if needed.

[Fuchsaudio]

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.