Behringer GMX212 amplifier problem

[mateplay]

This amp once warm, starts to build up a hissing/static noise periodically. Once it builds, then it goes quiet until the next build up. Ghost? Sure would like a hand to trouble shoot or a schematic if available. Thanks.

[Enzo]

What controls affect this noise and which do not? In other words, when it makes this noise, can you turn the noise down with any of the volume or gain controls, and do any of the tine controls affect the "tone" of the noise? This will help us isolate the problem to a certain stage. I suspect you have a noisy op amp.

[mateplay]

Good questions, I'm not quite sure. I have a friend who has the amp and I won't be able to check that until it returns next week. Is there a way to tell what stage it is in without a schematic even if you turn a knob and find a different result with a different knob? If a tone circuit is causing the problem it will still be present in the amp stages-right.

[Enzo]

Not sure what you mean. All amps are a signal path through a series of stages. At various points along the line there will be controls for gain, EQ, volume, whatever. ANy control that affects the sound in any way is after the source of the sound. COntrols that have no effect on the sound are before its source.

SO if the gain control has no effect, but the volume control does, then the noise is coming from between them. And if the EQ has an effect, then the EQ is after the source of noise. All the controls and stages are in some order, which stays the same.

If all controls affect the noise it may well be coming from the input jack board. Look at the input jack, is it not on a small board with a few parts? Without looking it up, I think there is a small one stage FET amp circuit right at the jack. COuld be a noisy FET even.

If you can narrow down which things are on which side of the noise, I might be able to direct you to the problem area.

[Adambrannon]

I, too, am having this same problem. After the amp warms up, it will start to pop and crackle. Past experience tells me it is in the poweramp section but not sure. I don't think the controls had any affect on the 'sound' of the crackle but can't be sure. It will do it whether there is an input plugged in or not. I'll fire it up and check for any signs of the preamp affecting the sound of the crackle.

[uncledom]

For techs only. Whilst investigating this and other issues inside the GMX212, I discovered two things. First, the data cabling is not shielded - common practice, but they glue them to the case for better shielding. Second, there is a 10 way cable that connects the DSP board at the back to the front controller panel. It appears to be plugged in before the others and then is flattened to the bottom of the case by the larger cables above before gluing. When this happens, sometimes the strain relief on the transitional plug on the DSP board, the connector at the front control board and the cable itself are subjected to such stress that the connections, the conductors - you name it - start to fail. this cable can be 'tapped' with an insulated non-cnductive item or such and produce the 'pop' sounds that emanate from the end of your static crescendo problem. I believe any overly loud hum behind it all could well come from a problem in the input jack CCT.

[SchnauzerLogic]

Thank you thank you thank you!!!

For techs only. Whilst investigating this and other issues inside the GMX212, I discovered two things. First, the data cabling is not shielded - common practice, but they glue them to the case for better shielding. Second, there is a 10 way cable that connects the DSP board at the back to the front controller panel. It appears to be plugged in before the others and then is flattened to the bottom of the case by the larger cables above before gluing. When this happens, sometimes the strain relief on the transitional plug on the DSP board, the connector at the front control board and the cable itself are subjected to such stress that the connections, the conductors - you name it - start to fail. this cable can be 'tapped' with an insulated non-cnductive item or such and produce the 'pop' sounds that emanate from the end of your static crescendo problem. I believe any overly loud hum behind it all could well come from a problem in the input jack CCT.

I have been looking for a solution to this problem with my Behringer GMX110 for over 5 years (even a local authorized repair shop couldn't figure it out), but this morning just before pulling the speaker out of the cab (for parts) and tossing the darn thing away I took one final pass through Google and stumbled across this thread. I didn't think the ribbon cables could have an impact but as I started to move the smaller one connecting the front panel to the board around there was a loud POP and that lead to a huge smile on my face! I powered down the unit and removed all of the glue from all of the cables (maybe close to 15 years old at this point) and wiggled/reseated the ribbon connectors and the amp has been working perfectly the last few hours. Wish I could buy you a beer, but good karma is definitely coming your way.

Thanks!
Robin

[Behringer amp problem]

I had to send this message hope you receive!! I bought a behringer vtone 30 watt New Years ago liked the idea of vintage design Jensen less than six months later the amp crackled on its own I called a repair shop who said they can't get schematics for that amp so I never got it fixed was debating selling it now I have other amps for some reason it came to me to google the problem and found your message! As well as the other person I Thankyou so very much I removed some glue used deoxit and reseated the connectors of the ribbons and no more crackling!!!!! Thankyou