Using two amps and 50 hz cycle hum

[Steelpriest]

Today I took out my old active AB box in order to use again 2 amps and selecting their inputs by a footswitch. The AB box sends the guitar signal either to the one amp or to the other. So far so good... but again I have this annoying 50 hz cycle hum (you guys in other parts of the world may have a 60 hz hum, ) because the both amps grounds are connected to each other. What do I do, and what do lots of other musicians do? I cut off the grounding/earthing of one of the amplifiers AC powerline. This helps. But I do not feel comfortable with it. On almost every amp there is a warning that says "This apparatus must be earthed!" But this practic I described is most common. Also I heard it is well okay to do so because when you have connected the two amps with each other over the ground of the input cables the amp without an earth is now earthed or grounded over the other amp's AC powerline. Is this true? Or do I have to worry? Any comments? Again: I would never use a single amp without grounding or earthing, I use two amps but only one of them has an AC powerline earthing. Okay, I know I should use a better AB switching box with galvanically isolated outputs but those ones are quite expensive. *sigh* I hope someone can help me out? Maybe Zac, the old PA rental man? ;D

[CAFeathers]

Try plugging the amps into plugs that are on different circuit breakers. If there are flouresent lights, a TV, a computer, or any other major appliance plugged into a plug on the same circuit breaker that will also give you hum.

[Steelpriest]

Thanks for your quick reply here, Chet. But it has nothing to do with the computers that are run on the same circuit. The hum does not appear when only one amp is used. There is only hum when both amps are connected at one time over the AB switch box and thus are inputwise connected to each other concerning the ground signal. When I pull off one of the input plugs the hum stops immediately. I don´t know the correct technical english term, in german we call it a "Brummschleife" i.e. in english a "hum loop", lmao. So I always cut off the earthing on one amp´s AC power line to avoid this hum. It works. The questions is: Is the amp without earthing indeed earthed/grounded over the other amp's wall socket? Of course they must use the same circuit then. Maybe I have to add that german power lines and wall sockets always carry three connections, I don´t know if it is the same in the USA? We have phase, zero conductor and groundwire.

[MARSHALL6PACK]

hey...have you tried a circut/surge protector, with the filters built in. ? they look like a extension cord, but have fuse,say like 4-5 outlets, on /off switch, and the really good ones have filters for noise protection. they are mostly for computers......maybe that would help. check around if you have some computer guros...see wjhat they have to say.
sean

[supedupviper]

That makes sense, seeing how those surge protectors have a grounding prong. Im using one right now for this computer

[MARSHALL6PACK]

i have a small question, what is the brand of the A & B box your using. is it just a basic switch , or is it battery /ac powered ? ive always wondered how you can use 2 amps...feeding off of each other. does a guy have to have the A & B unit...or is there another way?
sean

[Steelpriest]

It´s a NOBELS A/B box. A simple switcher but 9 V battery or 9 V DC adapter powered. So this is an active switcher. It also has two volume pots to adjust the signal power. You would lose lots of a guitar signal wich a passive switcher. This little tool here is very nice. It is even remote controllable with an external foot stomper. It has jack input for that purpose on the side. This means you can build-in this unit in your rack in order to keep signal wires short.



The brand of Nobels offers a great variety of nice little solutions for all kinds of signal routing. www.nobels.de The site is also in english. Take a look.

Back to my original question now. All is fine and well okay. When you use two amps in a set up you can eliminate the earthing/grounding of one amp. But you have to keep in mind to re-earth it when you use it alone again. I am hum-free and happy now!

[MARSHALL6PACK]

great news then....glad its working right. ya all you gotta do is get a new plug for the groundin/earthin. that will work. hey steel, or any one else. before they invented the a-b switch...how did the rock stars of yester-year run 2 amps at a time. just curious.....
sean

[Steelpriest]

There must have been things alike back in yesteryear... Or do you remember the old non-master volume plexiheads or the JTM 45 from Marshall? They had 4 input jacks, two high and two low sensitive ones. You could plug the guitar into one of them and re-route the signal out of the other jack of the same kind and connect to another amp or even to the low input of the same amp, what gave you another interesting sound variety.

[MARSHALL6PACK]

very good , this is kinda what i thought...so hear is another..on todays style amps...do you think you could get the same results using the effects input that most amps today,have to get the same over all effect.? runnin the signal out of the effects out and then into amp #2s input of its effects in....make since ? kinda funny how i typed it, but seems one should be able to try it...maybe. as always i look forward to any and all answers....thanx my bro....
sean

[Steelpriest]

It should work as long as it is a parallel FX out jack. You would use the the second amp only as a power amp then. You could do the same thing with the preamp-out jack.

I HAVE TO SAY THE FOLLOWING: Forget what is written above, I talked to lots of technicians and the only proper solution to cancel unwanted 50/60 hz cycle hum when using two or more amps is to use an isolation box. Indeed, one should never cut off the grounding from the AC wall plug. It can bare in any case a certain danger. I must say this here because I do not want anybody of you to get harmed. An electric guitar amplifier must be earthed IN ANY CASE over it´s own AC power plug.

[MARSHALL6PACK]

ya i never mess with me power cords. so ill try the in & out of the inserts and see what happens....im pretty close to gettin me another amp...so ill keep us all posted with the results.
sean