V-Amp Pro buzzing like mad

[stevie]

Just bought a Behringer Bass V-Amp Pro. I plugged it in to the preamp/line in on my Trace head and it buzzes like crazy. It's unusable. I'm not exaggerating - it's dire. It sounds fine through headphones via the phones outlet. However, if I take a signal from the phones out into the Trace, I get the same awful buzzing. All the various unbalanced outs on the Behringer are the same (pre DSP, post DSP, line out, etc.)

The buzz sounds just like the slight physical buzz that I can hear from the mains transformer on the Behringer if I listen very closely. The ground lift on the Behringer makes no difference, but I suspect that may not be working.

Now, the odd thing is that I don't even have to switch the Behringer on for this to happen. As long as the the power lead is in the Behringer and plugged into the wall (the wall outlet can even be switched off), and the unbalanced out is plugged into the Trace, I get the buzz.

This does not happen with my TC Electronics preamp, which is as quiet as a mouse when plugged into exactly the same mains sockets and amp.

All right, sleuths, you have all the information you need. Enlighten me!

[stevie]

I plugged the Behringer in to my M-audio USB soundcard connected to my laptop and then my hi-fi. No problem. Sounds great through all outputs.

The plot thickens. And no answer in sight. C'mon guys, somebody must know something.

[BOD2]

Which outputs on the V-amp are you using ? Is it an XLR output or a jack output ?

And the input on the Trace - is it XLR or jack ?

[stevie]

[quote name='BOD2' post='643490' date='Nov 2 2009, 03:41 PM']Which outputs on the V-amp are you using ? Is it an XLR output or a jack output ?

And the input on the Trace - is it XLR or jack ?[/quote]
I'm using the various unbalanced line outputs from the V-Amp into the unbalanced line in or power amp in on the Trace. Both mono jacks.

[danlea]

Do you not have an earth lift on the Trace to try?

[stevie]

[quote name='danlea' post='643792' date='Nov 2 2009, 08:09 PM']Do you not have an earth lift on the Trace to try?[/quote]
Yes, and I've tried it but it makes no difference. Isn't it designed to work with balanced connections? When I tried the earth lift, I still measured continuity between the earthing point on the IEC socket and all of the jackplug earths, although I've no idea how significant that is - if at all.

[BOD2]

Bearing in mind that there could be a fault....

It's still worth trying a few settings. Do you have the user manual ? It's truly awful but there are a couple of things in that that are useful - in particular the explanation of the operation modes and what signal is sent to what output depending on which mode is selected.

If you want all amp models, FX, and speaker simulations output, then connect to the RIGHT Analogue Out jack and use mode S1, S2 or L1. Obviously stereo FX can't be used in this mode.

Try experimenting with the volume and gain levels of the V-amp. Is it possible that the volume is just way up full ?

Beyond that, there's not much else you can adjust with regard to the outputs.

[BOD2]

Oh ... I should add - check that the V-amp isn't picking up external noise. Try moving it to another location away from the amp and any power cables or power adaptors just to rule this out.

[stevie]

[quote name='BOD2' post='643850' date='Nov 2 2009, 08:53 PM']Oh ... I should add - check that the V-amp isn't picking up external noise. Try moving it to another location away from the amp and any power cables or power adaptors just to rule this out.[/quote]
Good point. I'll try moving the V-Amp well away from the Trace later today. Funny that the TC Electronics preamp isn't affected though, using exactly the same instrument lead and mains cable and sitting right on top of the Trace. I'm using a 1-foot instrument cable into the Trace power amp input.

Re your earlier post, BOD, the hum occurs on all the unbalanced outs from the Behringer, even when the Behringer is switched off (and the mains socket is switched off). The hum goes away if I disconnect the mains lead from the V-Amp or if I unplug the signal cable between the V-Amp and the Trace.

Edited November 3, 2009 by stevie

[7string]

Try [url="http://www.guitarnuts.com/index.php"]Guitar Nuts.[/url]

Loads of info on solving buzzes and noise.

I think this is the 3rd time I've recommended this site this afternoon! It is good for wiring/shielding/noise though.

[BOD2]

It does sound a lot like an earth/ground loop.

Other than the ground lift switch (which you say doesn't seem to work) there's not a lot you can do when the gear is linked with a mono jack lead.

I'm assuming that both amp and V-amp are plugged into the same 13amp socket ? If not, then try doing that.

The reason the TC Electronics doesn't have a problem will be to do with the way it is earthed internally, which must be different to the V-amp.

[stevie]

OK, thanks guys, I appreciate the help. I looked at the Guitar Nuts site, 7 string, which is excellent, but doesn't give me the very specific answer I need. The two units are plugged into the same power socket, by the way, BOD.

I moved the Behringer away from the Trace - no difference. I plugged my battery-powered compressor between the Behringer output and the Trace - no difference. However, if I plug the Behringer into the standard bass guitar input on the Trace (rather than the power amp section input), the buzzing is still there, but at a *much* lower level. With the master volume (power amp volume) at zero, I can turn the preamp volume up full and the the buzzing stays the same. It only increases when I turned the master volume up.

When I get around to doing it, I'll be using the balanced out into a separate power amp anyway. I would like to know what the devil is going on here.

Edited November 4, 2009 by stevie

[Paul_C]

part of the problem might well be that it's a Behringer product - not always the best quality, which is why they're cheap

[danlea]

[quote name='stevie' post='643835' date='Nov 2 2009, 08:45 PM']Yes, and I've tried it but it makes no difference. Isn't it designed to work with balanced connections? When I tried the earth lift, I still measured continuity between the earthing point on the IEC socket and all of the jackplug earths, although I've no idea how significant that is - if at all.[/quote]

Is it the rocker-type earth lift, or a white button? My amp as both - one for the whole amp (rocker), the other just for the balanced outputs (button). If the earth lift switch makes no difference where it should, you might want to investigate. Perhaps try disconnecting the earth connection in the plug to give you a DIY earth lift (not that you'd want to leave it like this as a solution)?

[BOD2]

[quote name='danlea' post='645912' date='Nov 5 2009, 01:34 AM']Perhaps try disconnecting the earth connection in the plug to give you a DIY earth lift (not that you'd want to leave it like this as a solution)?[/quote]

I can't emphasise enough that this is NOT a good idea.



I can see why you are suggesting this as a method for identifying the problem, but it doesn't provide a solution and if removing the earth from the plug did make a difference then there would be a temptation to leave it this way. What could then happen is the unearthed power lead gets mixed up with others at some point in the future and gets used unwittingly with other equipment with potentially lethal consequences.

Please do not remove the earth connection from a mains plug for any reason.

[stevie]

[quote name='BOD2' post='646111' date='Nov 5 2009, 11:28 AM']Please do not remove the earth connection from a mains plug for any reason.[/quote]
I'm typing this message from a bed in the A and E department of the local hospital. Fortunately, the ambulance arrived quickly and had a cardiopulmonary resuscitator on board. As I am finding it difficult to stop my typing fingers shaking, I might not be posting for a while. However, I will be happy to read and try out more of your ideas when I get back home.

[TPJ]

heh heh, that stings a bit.

Have you tried another kettle lead or two?

Also, I bought one of these used. It has a horrible noise going on all the time too, like the sub harmonic effect is on all the time.
This comes through the headphones as well as all the outputs. When hooked up to a power amp and speaker, it's quite pronounced.

If it's new, maybe you can return it for another.

Edited November 9, 2009 by TPJ

[danlea]

[quote name='danlea' post='645912' date='Nov 5 2009, 01:34 AM']Perhaps try disconnecting the earth connection in the plug to give you a DIY earth lift (not that you'd want to leave it like this as a solution)?[/quote]
[quote name='BOD2' post='646111' date='Nov 5 2009, 11:28 AM']I can't emphasise enough that this is NOT a good idea.

I can see why you are suggesting this as a method for identifying the problem, but it doesn't provide a solution and if removing the earth from the plug did make a difference then there would be a temptation to leave it this way. What could then happen is the unearthed power lead gets mixed up with others at some point in the future and gets used unwittingly with other equipment with potentially lethal consequences.

Please do not remove the earth connection from a mains plug for any reason.[/quote]

I suppose I shouldn't assume that people on here are aware of the implications of disconnecting an earth connection. I did only suggest it as a diagnostic procedure (since the plug is easier to open than the amp), but I didn't emphasise the warning not to leave it like this - that would obviously be asking for trouble.

[BOD2]

[quote name='danlea' post='649193' date='Nov 8 2009, 09:57 PM']I suppose I shouldn't assume that people on here are aware of the implications of disconnecting an earth connection. I did only suggest it as a diagnostic procedure (since the plug is easier to open than the amp), but I didn't emphasise the warning not to leave it like this - that would obviously be asking for trouble.[/quote]


No problem. I'm just aware that this thread could be around for a while and there's always the possibility that someone might read it out of context, so I thought it best to emphasise the "safety angle" !