amps interaction

Gregory Altman · Post by **Gregory Altman** » 15 Dec 2015 4:07 pm

Im using a goodrich l120 pedal with 2 amp outputs. I have run both outputs into 2 amps before but when i try to use my new OLD evans fet500lv with peavey nashville 112, all i get from the nashville is a loud hum. Could it be something to do with the input of the evans. Any helpful input would be helpful

Jerry Overstreet · Post by **Jerry Overstreet** » 15 Dec 2015 4:42 pm

Hi Greg. Welcome to the forum.

Does either amp hum when used by itself? If not, then you probably need to lift the ground on one of the amps. You can try a 3/2 adapter on one or the other electrical cords temporarily and see it that removes the hum. There are devices on the market that address this issue permanently if you find that is your problem.

If either amp has a ground - + rocker switch, try different positions.

You say you have used 2 amps before without the problem? Was one of the amps cord grounds lifted or removed?

Gregory Altman · Post by **Gregory Altman** » 15 Dec 2015 5:23 pm

Hello jerry. Ive ran this nashville 112 amp with another nashville 400 or a peavey tnt 130 bass amp and even a fender super sonic 60 tube amp. I am hooking the evans up and all is good. When i hook up the 112 then all i get from the 112 is hum. No output guitar wise. Just hum. I ve thought about the 60 cycle hum. Since posting, i ve noticed that the input on the evans goes straight to a jfet transistor. Reckon that would have anything to do with it

Jerry Overstreet · Post by **Jerry Overstreet** » 15 Dec 2015 6:01 pm

Ya' got me. I can see 60 Hz. noise or hum being introduced when hooking 2 amps together like we do sometimes, but I don't understand how a signal can backfeed through the vp and kill the output of the 112.

If everything else works like it should, same vol. pedal, cords and all then it must be something specific to the Evans. FET's are just transistors, so I don't see how that or any amp design would do this.

Maybe someone else with some real electronics expertise like Ken Fox will look in and have some ideas for you.

Craig Baker · Post by **Craig Baker** » 15 Dec 2015 8:01 pm

George,
Not familiar with the input circuitry of either the Evans or the 112. However, depending on the circuits involved, possibly a voltage is leaking back out of the Evans that is shutting down the input stage of the 112.

Keep in mind, when plugging both amps into the output jacks of the pedal, you are connecting them directly together with no isolation.

Do you have any device you could use before the 112, probably any kind of pedal could be used as a test.

Best regards for a wonderful Christmas
Craig Baker 706-485-8792

cmbakerelectronics@gmail.com

C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024

Stephen Cowell · Post by **Stephen Cowell** » 15 Dec 2015 8:06 pm

You have a ground loop... Google it up and try what you find. I don't recommend removing the safety ground on one amp, but that would fix the noise, at risk to your person.

Jerry Overstreet · Post by **Jerry Overstreet** » 16 Dec 2015 6:52 am

We addressed the ground loop issue in my second post. I think Gregory has ruled that out as the cause. Anyway, in my limited experience, I've never seen a simple ground loop kill the output of the second amp as he states in his later post.....but there are many things that I've never seen and I'm certainly not a knowledgeable electronics technician.

Erv Niehaus · Post by **Erv Niehaus** » 16 Dec 2015 7:58 am

Maybe it's the cord going from the pedal to the amp.

Ken Fox · Post by **Ken Fox** » 16 Dec 2015 8:17 am

Classic ground loop hum

Keith Hilton · Post by **Keith Hilton** » 16 Dec 2015 10:49 am

Maybe a ground loop, but there is another possibility. The two amps have a common input ground, because of both being hooked to the pedal. Different amps can have a different ground "potential". A different ground potential can cause lots of hum and a ground loop effect. I have experienced this when trying to hook up a solid state amp and a tube amp. The tube amp had a much higher ground potential, and there was "lot" of hum. I have not had time to work on it, but someone should invent a device that makes the ground potential for two amps the same.