Running line out from any amp to another amp has a hum/stereo

[rio]

I’ve started messing around with a stereo setup with what I have before investing in it to be sure I like it. So far so good as it is has only been a few days - tried it with an organ trio today and it really expands the sound. I know the answer might be to get a stereo reverb pedal or something but I’m curious about this.

First thing I tried it running my Monoprice amp from its line out (which doubles as the fx send) to my Polytone. There is a bit of a hum and I can dial it out with the eq. I tried it with other amps out of curiosity, either with a dedicated line out or fx send and I get the same noise every time.

I imagine there is some reason for this. I read online to try a pedal with a ground lift between the two amps, and I tried that but it makes no difference. I like running the line out from the Monoprice because the volume on that amp controls the line out volume too so I just set the Polytone to be equal volume and then control both volumes from the Monoprice. I also get the benefit of it acting as a tube preamp in front of the Polytone and I like the sound so ideally I prefer this over getting a stereo pedal (although I can see the benefit of a stereo reverb pedal expanding the sound).

So first of all, if there a solution to this? Someone online also mentioned a DI box between the amps and I don’t understand why that would help (it might but there wasn’t any explanation). Any ideas why it’s happening?

And as for the stereo setup, do any of you guys do that? If so how do you do it? At a minimum I am excited to be able to hear myself better at gigs and at the most I think the sound of a tube amp and Polytone together really makes a sound I like a lot while also pushing sound more evenly into a room.



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[neilspeers]

I would use an A/B/Y pedal which sends the signal to either or both, running from one to the next in daisy chain fashion would - to my thinking- invite trouble, and wouldn’t actually be stereo.

The other thing you could use is a stereo delay or stereo chorus which would add some more separation between the amps - you can set the effects almost imperceptibly low and still get a cool effect.

But if all you want is a clean / dirty mix (which can sound awesome) or even just doubled up amp, the A/B/Y or stereo effect pedal turned off would work well

[rio]

I would use an A/B/Y pedal which sends the signal to either or both, running from one to the next in daisy chain fashion would - to my thinking- invite trouble, and wouldn’t actually be stereo.

The other thing you could use is a stereo delay or stereo chorus which would add some more separation between the amps - you can set the effects almost imperceptibly low and still get a cool effect.

But if all you want is a clean / dirty mix (which can sound awesome) or even just doubled up amp, the A/B/Y or stereo effect pedal turned off would work well

I just tried something that is confusing me. I have a large looper that has a stereo out, which I almost never use on gigs so I hadn’t tried it. Well I just tried it and even without an instrument plugged in I get hum when both amps are connected to the L and R outs. Unplug either one and the hum disappears. So it seems to be the exact same hum I get from the amps using the line out...if the looper is giving me the same hum then I’d imagine a stereo delay or reverb or something would too and I can’t seem to figure out why this hum is appearing. The hum doesn’t get any better or worse when the guitar is plugged in, it seems to be either connecting two with a line out or separately with the stereo out of the looper give the same hum and if I disconnect one side or the other then the hum from both amps disappears. Maybe I’m searching for the wrong thing but google isn’t helping with this one.

Edit: Aha, I think I might have found something through google. Someone said NOT to lift the ground by using a three prong to two prong adapter. So with that in mind as a potential solution (which I will not try as they were clear about the danger there), do any of you think a hum eliminator would be worth getting? If so would it go between the two amps or between the first amp and my guitar?

Sorry for the basic questions here. I am familiar with dealing with ground hum with guitar wiring but I guess I lack basic understanding enough to really get why this is happening with two amps.


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[Jabberwocky]

Sounds like a ground loop issue. Only ONE of your pieces should be electrically grounded to the mains; lift the ground on the other pieces. Of course, make sure that you have grounded mains. Not every 3-pin wall socket is grounded given lax building standards...

The other solution is an isolation transformer that isolates your equipment from mains AC ground noise. The isolation transformer goes in between your electrical power strip and the mains. Plug all your equipment into the power strip. The isolation trans plugs into the mains in the wall.

[Jabberwocky]

Recording Magazine Resources: AC Power Handling For Your Studio

[rio]

Thanks, that’s extremely informative and helpful to understand some of this stuff.


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[andyb]

This should answer some of your questions.

[mad dog]

Don't know about the stereo out method, but I have used two amps a bit. Daisy chaining can work, say from a 4 input tweed to a second amp. The cost is lesser signal to amp two, and the hit or miss nature of ground loop. A/B/Y passive splitters work also, but with signal loss and possible ground loop. Powered, isolated A/B/Y switchers are an excellent solution. Many out there ... the Radial Twin Cities is the one I like. No signal loss, and has a phase switch so you can eliminate the hum if it occurs.

[lawson-stone]

I’ve started messing around with a stereo setup with what I have before investing in it to be sure I like it. So far so good as it is has only been a few days - tried it with an organ trio today and it really expands the sound. I know the answer might be to get a stereo reverb pedal or something but I’m curious about this.

First thing I tried it running my Monoprice amp from its line out (which doubles as the fx send) to my Polytone. There is a bit of a hum and I can dial it out with the eq. I tried it with other amps out of curiosity, either with a dedicated line out or fx send and I get the same noise every time.

I imagine there is some reason for this. I read online to try a pedal with a ground lift between the two amps, and I tried that but it makes no difference. I like running the line out from the Monoprice because the volume on that amp controls the line out volume too so I just set the Polytone to be equal volume and then control both volumes from the Monoprice. I also get the benefit of it acting as a tube preamp in front of the Polytone and I like the sound so ideally I prefer this over getting a stereo pedal (although I can see the benefit of a stereo reverb pedal expanding the sound).

So first of all, if there a solution to this? Someone online also mentioned a DI box between the amps and I don’t understand why that would help (it might but there wasn’t any explanation). Any ideas why it’s happening?

And as for the stereo setup, do any of you guys do that? If so how do you do it? At a minimum I am excited to be able to hear myself better at gigs and at the most I think the sound of a tube amp and Polytone together really makes a sound I like a lot while also pushing sound more evenly into a room.



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If your Polytone has an effects loop, run the Monoprice effects send to the Polytone effects return. See if that makes a difference

[lawson-stone]

I just tried something that is confusing me. I have a large looper that has a stereo out, which I almost never use on gigs so I hadn’t tried it. Well I just tried it and even without an instrument plugged in I get hum when both amps are connected to the L and R outs. Unplug either one and the hum disappears. So it seems to be the exact same hum I get from the amps using the line out...if the looper is giving me the same hum then I’d imagine a stereo delay or reverb or something would too and I can’t seem to figure out why this hum is appearing. The hum doesn’t get any better or worse when the guitar is plugged in, it seems to be either connecting two with a line out or separately with the stereo out of the looper give the same hum and if I disconnect one side or the other then the hum from both amps disappears. Maybe I’m searching for the wrong thing but google isn’t helping with this one.

Edit: Aha, I think I might have found something through google. Someone said NOT to lift the ground by using a three prong to two prong adapter. So with that in mind as a potential solution (which I will not try as they were clear about the danger there), do any of you think a hum eliminator would be worth getting? If so would it go between the two amps or between the first amp and my guitar?

Sorry for the basic questions here. I am familiar with dealing with ground hum with guitar wiring but I guess I lack basic understanding enough to really get why this is happening with two amps.


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I'm guessing that what's happening is the hum is probably present in the first signal but not audible; but when that signal gets amplified in the second amp, the hum is boosted?? Not an expert, just thinking along with you here. I have those amps, maybe I'll try mine and see what happens.

[takauya]

It's wet/dry or dual-mono, right? Are you really running your two amps in stereo? If so the only person who can possibly hear the stereo image is you!

[John A.]

I’ve started messing around with a stereo setup with what I have before investing in it to be sure I like it. So far so good as it is has only been a few days - tried it with an organ trio today and it really expands the sound. I know the answer might be to get a stereo reverb pedal or something but I’m curious about this.

First thing I tried it running my Monoprice amp from its line out (which doubles as the fx send) to my Polytone. There is a bit of a hum and I can dial it out with the eq. I tried it with other amps out of curiosity, either with a dedicated line out or fx send and I get the same noise every time.

I imagine there is some reason for this. I read online to try a pedal with a ground lift between the two amps, and I tried that but it makes no difference. I like running the line out from the Monoprice because the volume on that amp controls the line out volume too so I just set the Polytone to be equal volume and then control both volumes from the Monoprice. I also get the benefit of it acting as a tube preamp in front of the Polytone and I like the sound so ideally I prefer this over getting a stereo pedal (although I can see the benefit of a stereo reverb pedal expanding the sound).

So first of all, if there a solution to this? Someone online also mentioned a DI box between the amps and I don’t understand why that would help (it might but there wasn’t any explanation). Any ideas why it’s happening?

And as for the stereo setup, do any of you guys do that? If so how do you do it? At a minimum I am excited to be able to hear myself better at gigs and at the most I think the sound of a tube amp and Polytone together really makes a sound I like a lot while also pushing sound more evenly into a room.



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Upthread advice should help with the hum (seems like a combination of ground loop and mismatch between line-out and guitar-input to me). To play in stereo, I spilt the signal with a stereo chorus (stereo reverb works too, but I prefer chorus, even though I hate mono chorus).

I also sometimes "jumper" the signal from input 2 of a Fender amp (works on any amp that uses the fender preamp design) to the input of the second amp. But without some sort of time-domain processing, it doesn't sound particularly "stereo". It just sounds louder and like a blend of the two amp's timbres.

Of course the obvious solution is to trade in your Monoprice amp for a Stereoprice amp ...

John

[pauln]

Are both amps quiet when used alone?
Does the hum come from both amps or just one of them?
Do both amps use a three prong plug?
Are both amps plugged into the same service outlet?
What kind of cord are you using between the amps?
Did you try sending to other amps from the Monoprice?

[sgosnell]

Is the line out of the Monoprice a 1/4" or XLR? If it's XLR, and you're using a XLR/1/4" cable, you'll get hum. You can minimize it to some extent by moving the cable around, but you can't get rid of it. At least that's my experience. Pure XLR or pure 1/4" unbalanced cable runs are usually fine, but when you mix them, hum follows.

[lawson-stone]

One question that is percolating with some of us here, I think, is what you mean by "stereo." Typically that means the splitting of the audio to separate outputs in which each output is different and the combined experience for the hearer is richer because the two different sounds, the "image" is united. Another thing you might be wanting is simply wider sound coverage without increasing the sound pressure level. that is, all can hear but it's not "louder." If you want the former, "real" stereo, I think some kind of splitter and signal processing is needed. If you want the latter, then you seem to be working towards a practical solution with the two amps.

[neilspeers]

It should be noted you shouldn’t defeat the ground on the power to any gear, they should both be on the same circuit and probably the same outlet / power bar / power conditioner (best choice). But you can lift the ground on the guitar cable going to one of the amps.

This is my A/B/Y pedal - passive, very affordable and has the bells and whistles that should work for this kind of setup.




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[rio]

Thanks everyone for the advice and info. I ordered a cheap hum eliminator which will arrive tonight since in the amazon reviews people mentioned this fixing hum sending a guitar to two amps. They have a money back guarantee so if it doesnt work then no sweat.

To reply to some specific posts,

Are both amps quiet when used alone?
Does the hum come from both amps or just one of them?
Do both amps use a three prong plug?
Are both amps plugged into the same service outlet?
What kind of cord are you using between the amps?
Did you try sending to other amps from the Monoprice?

1- yes both amps are quiet when used alone
2- the hum comes more noticeably from the second amp (no matter which amps I’m using and I have tried 4 different configurations) but the first amp also has some hum.
3- yes both amps have a 3 prong plug
4-I have tried both amps in the same outlet and different outlets with no difference
5- I’m just using a normal instrument cable to connect them
6- yes, I’ve tried sending and receiving from all of the amps I have that either have an fx send or line out, as well as stereo out from my looper and I get the same hum in every situation.

Is the line out of the Monoprice a 1/4" or XLR? If it's XLR, and you're using a XLR/1/4" cable, you'll get hum. You can minimize it to some extent by moving the cable around, but you can't get rid of it. At least that's my experience. Pure XLR or pure 1/4" unbalanced cable runs are usually fine, but when you mix them, hum follows.

It is a 1/4” out.

One question that is percolating with some of us here, I think, is what you mean by "stereo." Typically that means the splitting of the audio to separate outputs in which each output is different and the combined experience for the hearer is richer because the two different sounds, the "image" is united. Another thing you might be wanting is simply wider sound coverage without increasing the sound pressure level. that is, all can hear but it's not "louder." If you want the former, "real" stereo, I think some kind of splitter and signal processing is needed. If you want the latter, then you seem to be working towards a practical solution with the two amps.

Yeah it’s not true stereo since two independent signals aren’t being sent out. I think there is some stereo effect since there aren’t two of the same amps and the different sounds combine in the air. I might mess around with a slight delay or reverb at some point but for now this is achieving what I’m looking for.

This should answer some of your questions.

Thanks, I will check that out tonight!


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[KirkP]

If your Polytone has an effects loop, run the Monoprice effects send to the Polytone effects return. See if that makes a difference

I was about to make the same suggestion. It’s best not to feed the output from one preamp into the input of another preamp. All that extra gain can add noise.

[rio]

I was about to make the same suggestion. It’s best not to feed the output from one preamp into the input of another preamp. All that extra gain can add noise.

Tried that just now, same noise. Just to test it I did try a two prong adapter and that significantly cut the noise, though not completely. I’m not sure what that means in terms of a solution but at least it is something. I got a “hum destroyer” from amazon today and it makes it even worse. Seems like a really garbage unit so I don’t know if some device like that will not work for me or if it’s just the quality of this one (it was the cheapest one they had, tried it just because some people did report that it worked for them while others said the same as what I’m seeing, which is really low quality inputs and an even worse signal after using it)

Edit: I also just tried lifting the ground on the end of the cable connecting the two amps. Made the noise worse, and that was something I have seen recommended a few times while googling around so I’m not sure why.


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[KirkP]

And as for the stereo setup, do any of you guys do that? If so how do you do it? At a minimum I am excited to be able to hear myself better at gigs and at the most I think the sound of a tube amp and Polytone together really makes a sound I like a lot while also pushing sound more evenly into a room.

I have two Jazzkats, and sometimes slave one off the other for more power or better sound dispersion. I drew the following diagram showing how I connect them, and included a photo. The amp on left is the master and right is the slave. I’ve never had noise with this setup. Both amps are grounded, plugged into the same outlet, and have no ground lifts or devices to break ground loops.

It’s not really stereo, but I can get a pseudo-stereo effect by using different EQ and reverb settings on the amps. They also have much different speakers. You can get a true stereo reverb effect by replacing the Y-connector with a stereo reverb pedal such as the Boss RV-6.

[rpjazzguitar]

If it's the usual ground loop problem, plugging one of the amps into a ground lift adapter (a three into two prong thingie) will eliminate the hum.

I have been told that this can be dangerous and that the proper way to do it is to use an isolation transformer.

[sgosnell]

KirkP's method should work, provided both amps have effects loops. Not all amps have them.

[John A.]

Tried that just now, same noise. Just to test it I did try a two prong adapter and that significantly cut the noise, though not completely. I’m not sure what that means in terms of a solution but at least it is something. I got a “hum destroyer” from amazon today and it makes it even worse. Seems like a really garbage unit so I don’t know if some device like that will not work for me or if it’s just the quality of this one (it was the cheapest one they had, tried it just because some people did report that it worked for them while others said the same as what I’m seeing, which is really low quality inputs and an even worse signal after using it)

Edit: I also just tried lifting the ground on the end of the cable connecting the two amps. Made the noise worse, and that was something I have seen recommended a few times while googling around so I’m not sure why.


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I think the problem is a combination of ground loop and and plugging a line-level output into a guitar-level input. You're getting ground hum, plus noise from the input overload and mismatched impedances. You fixed the ground problem by lifting one amp's ground. To fix the output/input problem you need to find a different way to plug into two amps (i.e., a y-cable or splitter of some kind, an effect that has a guitar-level input and stereo guitar-level outputs, or an input->input "jumper" if one of your amps has a Fender style input design).

John

[JaxJaxon]

just try it with a Y spliter adapter they are cheep.