How difficult is it to install a passive effects loop?

[mike9]

I have an 18 watt Trinity SIII TMB MV that a TGP'er built from a kit. It's a killer amp and I loaded it with NOS tubes. It compliments my Omega HRDLx really well, but I like having my wet signal post preamp. Is it difficult to install a passive effects loop, or is a tube driven loop better? Thanks for any and all intelligent advice.

[Funkalicousgroove]

A passive loop is just a matter of installing 2 jacks and a couple wires before the PI, an active loop will change the tone of your amp all together and will be alot more work.

[benoit]

Passive loop and a standalone dumbleator might be cool, no?

[mike9]

A passive loop is just a matter of installing 2 jacks and a couple wires before the PI, an active loop will change the tone of your amp all together and will be alot more work.

Than you - that was what I was hoping to hear. Do you think it's OK for a DIY project?

[Tonegeek]

+1 on what Funk said for the labor involved, but you may be disappointed in the results unless you consider the part of the signal chain you put the loop in and the voltage and impedances you are dealing with particularly when you bring the signal back into the amp. I put a passive loop in my Twin before the phase inverter and it works great, but one in the same location in a Marshall probably won't because the Marshall's usually expect a higher voltage which most effects units can't deliver. Translation: Low volume and distortion. If you post a schemo of your circuit indicating where you want the loop, someone here could probably tell you if it will work.

[rhubarb9999]

+1 on what Funk said for the labor involved, but you may be disappointed in the results unless you consider the part of the signal chain you put the loop in and the voltage and impedances you are dealing with particularly when you bring the signal back into the amp. I put a passive loop in my Twin before the phase inverter and it works great, but one in the same location in a Marshall probably won't because the Marshall's usually expect a higher voltage which most effects units can't deliver. Translation: Low volume and distortion. If you post a schemo of your circuit indicating where you want the loop, someone here could probably tell you if it will work.

Can you post more details on the FX loop you put in the twin?

[Tonegeek]

+1 on what Funk said for the labor involved, but you may be disappointed in the results unless you consider the part of the signal chain you put the loop in and the voltage and impedances you are dealing with particularly when you bring the signal back into the amp. I put a passive loop in my Twin before the phase inverter and it works great, but one in the same location in a Marshall probably won't because the Marshall's usually expect a higher voltage which most effects units can't deliver. Translation: Low volume and distortion. If you post a schemo of your circuit indicating where you want the loop, someone here could probably tell you if it will work.

Can you post more details on the FX loop you put in the twin?

oops. I may have been wrong about it being passive. I just pulled the scmemo and it is showing a passive send but active return. The send comes right after the last preamp tube where verb and channel comes back together. I did this mod 20 yrs ago with some other big changes at the same time so apparantly I had an extra tube triode left over which went for the loop. No wonder it works so well. Sorry to get your hopes up. see attachment

[David Root]

A properly designed active FX loop should not affect the amp's tone. Unfortunately they can be fairly complex, messy to add point to point and a LOT of work. Ask me how I know that.

Should be done in a PCB ideally, but still using a 12AT7 or 12AX7 if you insist on tubes only in the signal line. Good ie non colored SS designs do exist too.

[mumford]

David Root-- no wonder you stopped coming to the UT luthier meetings-- you live in AZ now.

I've been wondering about adding a loop to my express. Hmmm

[RedRock]

Take a look at the schematic for the Fender Twin II.
The effects loop in that amp has a send level control
and a return level control. It uses both sides of a 12ax7,
and is out of the circuit when nothing is plugged into
the return jack. The switching jack for the return is available
from Mouser Electronics. This was designed by Rivera when
he was with Fender in the 80s. It is an excellent series
effect loop. It takes an extra tube, and four chassis holes
for jacks and control pots and a lot of work!