Playing through a two-amp setup

Man, you are talking way over my head there. Phase correction? All I know is that the Morley is user-friendly. It has no noise when you switch. It does not affect tone.

Just so happens I was monkeying with my Morley today. The power of playing through two amps spread out in my music room is a cool trip.

I was also monkeying with my BOSS footswitch. If you don't have one of these, I'd suggest one. Great investment. Can turn things on and off cleanly, silently, easily. This one is also unlatch. Can do a momentary on or off.

 

I have the Switchbone too and it’s one of my all time top three purchases.

No affiliation either but a superb product. I normally use it with my Deluxe Reverb plugging into both channels and switching between the two or both at the same time.

I’ve also used it for amp switching. My favourite was using my DR and an AC30 than was onstage and belonged to another band playing that night. That was tonal heaven.

The clean boost is awesome and I use it for soloing.

Peter

 

Same socket for both amps and pedalboard is best.

 

Stumbled across this. Dave is a boss.

 

You want to make sure and share a ground. Using a power strip will do that. Using the two plugs on one wall socket is fine.

Using two completely different outlets on different walls “might” or might not share the same circuit.

 

Yes. This will prevent shock hazard and ground loop noise.

 

Are you on the road? Don’t text and drive!

Be warned, it’s going to sound huge! Be sure and post an update...

 

I disagree. Plugging both amps into the same socket *might* solve the ground loop hum issue. Might not.

The issue is that with both amps connected by many of the more basic A/B/Y pedals, or probably most any stereo pedal, there's no isolation. This means that the return leg (common, running to ground) is common to both amps. So, theoretically, an electron trying to find it's quickest path back to the wall, might not always take the direct route, right out of the amp. Instead, some current will likely flow through the common leg of the instrument cable running to the A/B/Y, and then out the other side, to the other amp, and then, finally out to the wall.

This creates noise.

The quietest circuit will have a very controlled path for the return, or common. Best practice these days seems to be to either elevate the common above chassis ground, and then feed it to the chassis at a single point only, or if not elevated, at least funnel all returns through one location for the preamp, and another location, far away, for the power section. This keeps high current flows from stomping on sensitive preamp inputs. Part of the problem is that most older (and even not so old) amps ground everything to the chassis, at any handy point. The whole chassis becomes one big ground plane, with potentially criss-crossing current flows at different potentials.

Even the best constructed amps (two of them) will suffer if there's one more path to ground introduced through the input instrument cable. Namely, back to the A/B/Y, then out through the other chassis.

An active A/B/Y, with an isolation transformer and ground lift, will eliminate the problem.


EDIT: the same situation exists when you plug an outboard reverb tank into your signal chain. You've got another "amp" (read: high voltage power supply, driving preamp tubes), which connects to the guitar amp in two ways. First, through the shared common at the wall. Or even different wall outlets, it's all ultimately 'ground'. And second, through the common leg of the instrument cable that connects them together.

It's more difficult to correct the issue here, because there's no A/B/Y with transformer involved. The same would be true with any effect pedal, not just some big tube 'effect' like the 6G15 outboard unit, except they're all ground-isolated from each other, and the amp. Either they're battery powered, so no wall connection, or they connect through a step-down transformer, which isolates at the same time as it converts 120VAC to 9VDC.

The preferred solution for the outboard unit, and the one which Fender uses in their reissue, is to 'elevate' the common above zero volts ground, and then connect to the ground only through a single point with a small network of resistor, cap, and safety diodes.

 

True, it might not prevent ground loop noise, but the OP’s main concern was with the safety of it, so I didn’t go into detail.

A good ABY with isolation, ground lift and is obviously the best solution, but it won’t hurt to try it and find out.

No need to spend the money if it works without doing so.

 

I’m glad @moosie weighed in with a much better explanation of the how's and why’s of what to expect than I am capable of.

You probably will end up with an ABY of some kind if you are serious about a two amp rig, and I recommend it. If I had owned a stereo pedal of any kind, I would have tried that first, for grins though. It works for some people.

I didn’t have one, and didn’t want to do stereo, but rather wet/dry and/or clean/dirt as well as either/or, so I went straight to a decent ABY out of necessity.

 

You know how it is, a thread goes on for days, and you've read it all, but not just now.

I forgot that was the intial concern, and I was just responding to @heshan's summary comment that "it should fix the noise issue".

Sorry if it got off-topic.

It's a hot button for me, since I just finished building a Revibe unit, which like the outboard reverb unit, is extremely susceptible to ground loop noise. I elevated the DC common, and it's quiet as a mouse.

 

You didn’t go off topic at all. Far from it, as he was concerned about possible noise as well. As I was writing I figured I would get called on the noise issue, but was too lazy (and ignernt) to try and explain all that stuff you explained so well.

Your only mistake was not weighing in sooner!

 

It is worth trying two amps, if you have the facility though, it does sound great.

I ended up getting a palmer splitter box powered by battery, which does the trick. It has the phase flipper and ground lift.

A time will come when I will want the radial, or something similar though.

 

Wow this was an interesting thread.

I've played through two amps for YEARS and never had, and never thought about, phase issues or getting zapped. Granted, all my amps are grounded.

I have never used an AB pedal, only stereo pedals (Boss DD-5/6, Fulltone Supa Trem 2, etc) and I've never had an issue, besides wanting to play for longer than I was able to, or maybe the volume getting too high.