using 1 effect in 2 guitar amps effect loops - Help please!

[mj_guitardude]

Hey guys and gals, I have a silly question that I can't seem to find an answer to anywhere.. here goes.

I have 2 amp heads, 1 clean and the other dirty. I have a tonebone switchbone to switch between the 2 amps and that works great but I recently purchased a deluxe memory man with tap tempo, which is very pricey and souds great! My question is, can I hook it up to both amps effects loop? The effect chain would be (I guess) amp 1 effect send into the delay's input. The delay out into amp 2's effect return. A patch cable would then connect amp 1's effect return to amp 2's effect send. Does that make sense? Will it work in keeping the actual 2 separate guitar amp's clean/dirty tones intact? I am gonna blow something up or ruin the DMM?

Any help would be great and I know, you can call me chicken for not just trying it out... :-)

Thanks again,

Marc

[Brad1]

Y'know...that's something I never considered...using one pedal effect looped through the effects loop of two amps. I don't think it can be done, and there a lot of considerations you need to take into account anyway.

Here's the problem with your proposed setup: A patch cable would then connect amp 1's effect return to amp 2's effect send.

Amp 1 sends it to the pedal, the pedal goes to amp 2's return. That MAY work to get delay to Amp 2, but it also gets everything in the preamp stage before the delay to it. AND,, at this point, if Amp 1 has a serial loop, nothing is getting back to Amp 1 effects return.

Now, here's the real problem, Amp 2's effects send won't send that back to Amp 1. Why? Because you injected the delay AFTER the send to continue to Amp 2's power section. Amp 2's effects send is AFTER the preamp section, and BEFORE the power section. The delayed signal is (probably) not available at the Amp 2 send.

ONLY anything introduced to the guitar input, or in the preamp stage, can be at either amps' effects send. It can't go backwards?

Some other considerations is whether the effects loops are serial or parallel, if either/both have input/output level controls, etc. Cumulative impedance mismatches may also be a factor, but since they are designed for pedals...maybe not much.

I just don't think you can loop two loops.

If one or both of the amps has a parallel loop, you COULD get the delay to the second amp from the first, but it would only be injecting the characteristics of the first amp's tone (preamp tube overdrive, tone controls, etc), you'd need a splitter to feed the delay back to the first amp's effects return and also to the second's return. AND, if you switched out the first amp and played into the second amp, you'd have no delay. All you'd have is the residual noise of the first amp's preamp plus the delay (with no signal going through any of it) riding along with the preamp signal of the second amp into its power section. In fact, unless the second amp has a parallel loop that mixes the signal, you may not get ANYTHING from it by switching out the first amp, because you've disconnected the second amp's preamp.

A serial loop may absolutely break the path between preamp and power section. If something is plugged into only effects out, nothing continues to the power amp. If something is plugged into only effects in, nothing in the preamp gets through.

Some may allow an injection MIXED into the power amp section by plugging into effects in only, but if plugged into only effects out, the signal may stop from continuing to the power section. Anything like that may have a level control...but I'm not sure there are many like that. The opposite may be true. You may be able to 'split' the effects out, to let it continue to its amp plus another, but plugging into the effects in ONLY may stop the preamp in its tracks.

A complete parallel loop should let you plug something into only the effects out without breaking the path to the power, and let you plug only into the effects in without breaking the path. Those may (will probably) have level controls, also. The idea is to let the effect (chorus, delay, etc.) "mix" into the signal, leaving the original signal unmolested. This can produce a cleaner sound, because you are only mixing in whatever level of effects you need.

Even IF two parallel effects loops would let the effects out back themselves into the effects in, you'd probably have nothing but a nasty uncontrollable loop, so that isn't good.

About the only thing you could do, I think, is buy or build some kind of a dual switcher that can switch the amps' guitar inputs AND the loops of the amps at the same time. The problem with that is that it would have to an 'either/or' situation. because the delay pedal has only one input, it can accept only one signal at a time...you cannot run the effects out of two amps into it at once, so you couldn't use both amps simultaneously.

Unless it had a circuit built in to properly isolate the outputs, and mix them back in. Then, you'd have a box with #1) guitar input; #2) and #3) guitar out to amp in; #4) and #5) pre-out (effects send) A and B; #6) and #7) amp-in (effects return) A and B. you'd need seven 1/4" jacks, and a couple of switches that can do double-(triple?) duty. Plus, a circuit if you wish to ever run both at once. The major problem with THAT, is you'll be mixing the clean/dirty/chorused/wah-wah/whatever from each amp into the other.

Or, you could use the Tonebone to switch the amps, and buy/build a switcher only for the loops, but you'll need to remember to switch those also, when you want to use the delay for each amp.

Am I even making any sense? Doesn't seem to me to be an easy way to do that. But, I may be wrong. I have been before. This is all just sitting here at 6 am, a couple coffees in, running this all through my head.

Anyway, tell us exactly what your amps are (brand/model/etc.) That may lead to more possibilities.

Good luck,

Brad1

[mj_guitardude]

Hi Brad!

Wow, thanks for giving this so much tough!

Both effect loops are parallel and don't have level knobs of any kind, they are a Marshall JCM 2000 DSL and a JCM 800 2203ZW; I have since also acquired an Orange Dark terror with the same kind of effects loop.

Let's add another element to this already complicated scenario: I also have a tonebone loop bone, which has 2 loops. It has 1in, one out, and between has ins/out for loops 1 and 2. What if the master in/out of the loopbone was hooked up to the delay (instead of the guitar and amp) and each loop then went in/out of each amp's effect loop? so it would be TB loop 1 send to amp 1's effect return, TB efect 1 return to amp 1's effect send, same for loop2/amp2 effects loop and the TB instrument in to the delay's out, TB amp out to delay's in? that would technically let me select which effect loop the delay is going to but I can only imagine the problems from having both loops engaged at the same time, (loop 1 + 2 on), then the whole amp slaving/impedance etc. problems would come in to play but would it work if I only used 1 loop at a time?

Thanks again Brad, I really appreciate your time and advice.

Marc

[Brad1]

Calling all gurus!!!

Wow..that was about as confusing as my previous post!

You could use a switcher, but it could ONLY be Amp 1 or Amp 2. You would have to disable, or not build in, an A+B merge, since you want to run it in and out of two loops.

Personally, I wouldn't trust anything that even had the POSSIBILITY of accidentally combining the preamp outs of two amps to one input of the pedal, and then back out to both power amp sections. One moment of inattention could create hours of fun repairing things, though!

You could have a switcher with an In and Out specifically for the pedal. Then, you would need an A in/out and B in/out. 6 jacks...3 in, 3 out. One button, switches the effect to either A loop or B loop...but NEVER both. Or, you may have two buttons, one for A/B and one for On/Off...leaving the effect on all the time, and just kicking it into the loop...saving an extra pedal-jump stomp. And, you'd have other considerations, like possible ground loops, pedal gain-setting mismatches per each amp, etc.

Consider, also, where you're going to place all this. If it's going to be stage-front with the rest of your pedals, then you can have relatively short cables from the effect to the switcher, but you'll have TWO longish cables, each, (four total) from the switcher to each amps' loops.

If you place the effect back by the amps, and the switcher stage front, then you'll have SIX long cables, since all cables go to switcher. Nix THAT idea.

If you place the effect up front, and the switcher near the amps, then you'll have four short cables (amps to switcher) and two long ones (effect to switcher). That would be good if you're NOT using an On/Off button on the switcher (or just leave it set "On"), want to leave the A/B switched to one or the other, and just kick in the effect from the pedal itself, on your stage-front pedalboard.

If both switcher and pedal were back by the amps, ALL cables would be shorter, but then you'd have to go back to engage/disengage or switch.

If either, or both, amps had serial loops, and one jack broke the path, then switching out would completely break the preamp-to-amp path, rendering no sound at all from the amp switched out. BUT, you say they are parallel, so breaking a parallel path shouldn't break the pre-to-amp path. And, cable length may not be QUITE as important on a parallel effect as it would be if the entire signal had to run serially through all that extra cable.

You may have to worry about creating loud "pops" when switching, but that can be tamed.

The thing is, you will NEVER be able to use that one effect on both amps at one time...unless you had a proper input mixing circuit built into the switcher. And, that might be interesting, but what will happen is that you'd end up mixing the characteristics of both preamps together to get delayed to go back to both amps' power sections.

Some of the stompbox gurus on here should be able to point you to an existing design/product...or if one doesn't exist...devise one fairly simply. Maybe even with active circuitry to control input/output levels, ground-lift schemes, malfuction-proof safety features to prevent possible shorting of both inputs, 'quiet switching', LEDs...stuff like that.

I just think you need to be VERY careful about what you are using, and if anything has even the slightest possibility of shorting two preamp outs together through confusion, inattention, accident, drunken bass player stumble-footing...whatever...I'd look for something else.

CALLING ALL GURUS...am I on the right track here? Anyone? I'm better with concepts than actual technological design. I'm more a tech, than an engineer...but I think what you want can be done. It's just a bit unusual. Heck, maybe I should see if a patent already exists for an "Amp Loop Looper" that does just this kind of thing? I'm sure some of the famous playes' techs/pedalboard builders have considered/done something like this. Anything exist on the market? Radial seems like a likely suspect to offer something. Maybe all they have to do is eliminate the "+"
in AB?

Brad1

[gavin_rossdale]

I am having my own issues with series loop, creating parallel mix effects and blending with amp. Hoping to have some suggestions from guitar how to experts..

[kleuck]

Buffer/Mixer/Spiltter

You can add an isolation transformer for a ground-lifted output

[J M Fahey]

Confusing thread and posts.
What the OP wanted, *can* be done, but using a complex switching matrix, with some relays and logic, á la Bob Bradshaw, but it sure will be more complex and expensive than you think.
You need to send both loop paths to a common switching box, which takes care of routing either send signal to the effect and getting it back to the corresponding loop return, *while* at the same time bypassing *the other* loop; doing the reverse when needed to send the effect to the other amp and last but not least, be able to send effectb to neither of them
You would need to add buffers when approppriate, offer some way to independently set signal levels, because both loops will send the same level only by chance, etc.
Solving ground, popping and clicking problems would still be an entirely different problem.
In a nutshell: it *can* be done, youŽll need somebody experienced to do it, and a single unit cost would certainly be too high.
Bob Bradshaw does it all the time, but his expensive customers can afford it.
This one is more complex than what you ask, but the grounding, logic, switching problems are already there:
Product :: Custom Pedalboard Switching System
Of course, he started humbly; hereŽs what he thinks was his very first switcher, "drawn on a napkin" and then successfully built (with lots of tweaking), 30 years ago:
The Bradshaw Legacy