The internal fan has been making noise and now after 30 min or so we get a loud pop the a descending whine at deafening levels even with the board muted. I'm suspecting an internal supply issue in our GL2400 32 channel mixer. Am i wrong or should I consider other problems.

Sounds like it might not be cleaned enough. They may have done the pots but the internal circuit boards may not have been done enough.

buy a canister cold spray and spray on some active components if the noise begins You have a thermical failure in a component on the board can be faltering resistorcircuits or resoldering some active components.

Hi J Wade. I'm Dave P. I'm not a guitar amp expert or technician but I've been using amps and effects for 35 years and there are a couple things I can suggest.

That kind of periodic noise/switch noise can be a symptom of having the polarity of the amp reversed. If your amp has a 3-position OFF/ground switch, try reversing the ground. If it doesn't, take the plug and turn it around. Just don't get near a microphone unless you're sure your amp is grounded the same as the P.A. It could fry your lips off.

Dirty switches to that too. You said the noise is in time with the delay's tap time which is set by a foot switch. If tapping that switch the first time generates a pop, the delay may have catch it and is repeating it. Turn off the amp, remove the delay foot switch and turn it back on. Still noisy? If not, give the foot switch a good cleaning.

When you turn the EFFECTS knob up, is it scratchy? Might need the potentiometer cleaned. What happens when you specifically turn the DELAY level down all the way while using the other effects? Noise still there?

That's all I've got. Hopefully, it was helpful. Don't wrack your brain over this too much. There could very well be an internal problem with your amp that will require a trip to the shop. You don't want to open it up yourself. Rock on but be safe.

Dave P.

This is because your clean channel only runs through the pre-amp section, requiring an increased volume level to match that of the volume of the drive section which is overdriven by the pre-amp circuit. my suggestion is to use lower volume level on the clean channel of the amp. To get any volume boost you may need to match the two channels you could use a signal/volume booster or overdrive pedal between your guitar and amp input, switching it off and back on when you switch back and forth between channels.

Make sure you use BALANCED interconnection cables and the board is powered from the SAME receptacle or source as the speaker/amp.

This board is very simple and if the source of the noise is in the unit, I would look to a problem involving the Phantom power supply. The Phantom connects to the mic inputs and if it gets noisy it will often couple into the inputs.

Unplug ALL inputs to verify it is not coming in via the mics. Does the main fader control the loudness?

Here might be your schematic:

http://elektrotanya.com/soundcraft_e8_mixer_sch.pdf/download.html

Have a look at this link:http://www.geofex.com/ampdbug/squeal.htm then Back to the Home Page. You may have a bad solder joint some place on the circuit board also. Unless you have experience with electronic repairs you are best served by consulting an accredited Marshall dealer and repair person as there are voltages present that can kill or injure you.

This often normal to get a pop as the power goes down. The amplifier goes out of balance as the power drops and it drives current into the speakers. This is a design problem and most amps don't even TRY to avoid it. Very large amps have relays that disconnect the speakers an instant before the power collapses to protect the speakers.

I suspect a bypass capacitor for the preamp section has failed. It needs to go to the shop and be tested with an oscilloscope to pinpoint the problem.

DO make sure the feedback is NOT from something you have plugged into it... make sure it is there with NO input cable plugged in. Often external devices can introduce ground loops an noise like this. Lamp dimmers (even stage lighting dimmers) can be a source of interference.

The sound you hear MAY not be the full loudness as the oscillation MAY be above your hearing range. This COULD cause overheating and damage so get it fixed before using.

Could very well be the fan. The motors can cause interference. There may be a solution to get rid of the noise. Some copper shielding tape may help. You could rule out it being a microphonic preamp tube by turning the amp on as normal and tapping the tubes with something non-conductive. If you hear the tapping noise coming thru the speakers while doing this to a particular tube, replace it. With power tubes, the tops of them turn white on the top when they become microphonic, along with plenty background noise.

Replace C21 (10uF/50V) and C38 (2.2uF/50V) and it will work great.