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Tech21 trademark 10 amp loud mains hum, with all controls at zero

Amp was working fine. Suddenly the only sound it produces is a loud mains hum. None of the amp controls have any effect upon this sound.

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I have an Fender Rumble 100. I've had it now for about 10 years. When I switch it on it has an loud hum. I don't want to get rid of it, because it been an good amp. What do that sound like the problem to...

I've included a link which provides information on some of the possible causes for hum in an instrument amp. If all else fails to locate the hum, the hum may be caused by a bad filtering capacitor, possibly in the power supply. I suggest you have the amp diagnosed by a reputable musical instrument shop. Troubleshooting Guitar Amplifier Hum eHow

May 26, 2014 | Music

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When I turn amp on there is a loud humming that does not stop.

try plugging into a different socket if that doesnt solve problem you may need to replace cord. sounds like a loose neutral in socket though.

Dec 01, 2012 | Fender Frontman 212R 100W 2x12 Guitar...

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Serial number 00-06778552, a gig amp manufactured about 1977/78, (used in an American tour in 1978). While running a practice session at low volume, the yellow DDT light blanked altogether (this has been...

The amp has a failure. One side of the power amp is starting to draw excessive current to the point that the filter caps can't sustain the current so the ripple starts to be heard in the speaker. Continued use MAY burn up the speaker by sending DC through it as well as causing additional damage to circuit boards, etc..

May 25, 2011 | Peavey Max 115 1x15 Bass Combo Amplifier,...

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My amp has no volume unless turned all the way up and only on the high input jack

check the "Gain" on the instrument you are plugging in ... if it is all the way down, that's the problem. If that's not it, check for a "Gain" control on the amp itself -- the is a volume control that takes care of the sound BEFORE it goes through the amp (pre-distortion etc.). Sometimes this is not with all of the other controls on the amp, so look carefully.
If it is not the gain on your instrument, and it is not the gain on the amp, then make sure you are not using too long of a wire to connect the two things. If you are using a 100ft cord to connect a guitar to an amp, there will be a lot of signal degradation in the wire, and it will be hard to get good volume from the amp since it is not getting enough signal to amplify.Try a shorter cord, and that might help ...
If all of these have failed, check the fuses on your amp. If there is a blown fuse anywhere, then your amp might not be getting the full power that it needs to produce the sound you are looking for (though a blown fuse usually cuts out ALL power through the amp, some models are built differently and this could cause your issue)
If none of these solutions work, try hooking the amp up to something else that you know works fine, to make sure it is the amp itself, not what you are hooking into it, that is not working right.
If all of this turns out to be an Epic Fail ... try speaking with customer service at the amp's manufacturer ... it might be a defect that they have seen before, and they may replace it, or at least give you a better solution that what I have done.

May 23, 2011 | Music

1 Answer

Buzzing noise when not playing

All amplifiers make a little bit of noise (hiss) but it is normally slight and drowned out by playing. However, assuming that this is not normal system hiss, here are a few simple steps to try and locate the source of the problem by process of elimination.
  1. SAFETY FIRST - a common cause of a humming or buzzing sound can be a lack of earth (grounding) on the mains supply. With a 240volt AC supply this hum will be at 50hz (in the UK) - frequency may vary in other countries but should be similar. Check the earth first because of risk of electric shock. Until you are satisfied that this is not the cause of the problem DO NOT touch any metal parts of the amp. Remove the mains lead and try a different one. Try plugging the amp into a different mains outlet socket (preferably one on a completely different circuit).
  2. Turn off other electrical equipment in the vicinity that may be causing interference. Move the amp a bit, try rotating it by 90 degrees to change relationship to things like mains electric cables in the floor.
  3. If you are using the line-out socket to give a feed to a mixer, slave amp or p.a. system unplug this. Sometimes double earthing (through the mains lead of your amp AND the mains lead of the MIXER / PA) will cause an 'earth loop' due to a different resistance at each end. Putting a DI box with an 'earth lift' in between may eliminate this problem. Alternatively there are little gadgets you can buy to do this (I found one intended for car audio systems on Amazon that works very well)
  4. Unplug any instrument leads - to eliminate possibilities of interference affecting cables, effects pedals or guitar pick-ups. Also unplug the foot-switch.
  5. If that stops it plug a lead in without a guitar on the other end - does the noise return? If yes change the lead. If no plug the guitar in.
  6. Try moving the guitar in relation to the amp (turn it around 90 or 180 degrees) - this will be pick-up to amp power supply interference.
  7. Does the sound get better or worse if you touch metal parts of the guitar with your hand? This may be a screening issue within the lead or the guitar itself.
  8. Try turning all the individual channel tone and gain controls to zero, turn off any effects on the amp panel. If that eliminates it only turn up the controls on channels that you are actually using.

Jan 30, 2011 | Marshall Amplification Marshall MG50FX 50...

1 Answer

The amp plays fine for about 15 to 20 minutes, then an extremely loud, over powering hum/buzz takes over, and then the amp has to be turned off, but the problem persists. I've tried several guitars,...

You say the "tubes are fine" I take it that you have either replaced them with new or used a very sophisticated tester on them. A heater-cathode short might cause the symptom. There are a bunch of tests I would want you to run alnd get back to me with the results.

Heat up the amp but DO NOT play anything into it for the usual failure time or more and they start to play i... did hum occur WITHOUT playing? With all volume controls down does the hum occur?

The right tools is an oscilloscpe to fing out if the filter caps are good. These are C31, C33, C35, C36.

With hum present in failed stater, plug in a grounded plug into the power amp in jack... if hum is stiil there, check the +/- 16 volts regulating Zener for ripple. get schematic here:

Jan 29, 2011 | Fender Hot Rod Deluxe Guitar Combo...

1 Answer

I purchased a pair of Hs80m. I am having a problem with one of them. The monitor works fine for about 10 mins. After about 10-15 minutes the monitor will make a humming sound then eventually blow out. The...

The powere amp portion is LIKELY going into thermal runaway where one side of the pushpull driver shorts out drawing heavy current to the point you can hear the ripple (hum) probably followed by fuse blowing. You need to have that unit repaired. Replacing fuses MAY be causing further damage.

Chances are IC601 or IC602 (LM3886TF-2) are defective or something in the DC feedback circuit.

Here is the service manual:

Of the two, IC601 is the most probable as it drives the woofer. Available...$7.30 from

Jan 09, 2011 | Yamaha HS80M Powered Monitors

1 Answer

When i power up the amp it makes a loud fuzzy wave sound then dies down a bit and you can play over it but the sound is weak and clunky. i took out the pre amp tubes and jiggled them around/cleaned some...

It sounds like your amp has one or more bad capacitors in the power supply. The AC mains input isn't being filtered properly, allowing hum and robbing the amp of the clean power it needs. It may be a case of bad solder connections, which is a very common problem in today's equipment. Another common trouble is capacitor failure due to under-rating the parts to keep cost down, leading to over-stressing and early failure. The shop you took the amp to should be able to check the caps and power supply operation, and replace any parts that aren't up to snuff.

Nov 23, 2010 | Peavey 6505 Plus 120W Guitar Amp Head

1 Answer

Marshall VS65R is powered up it hums

Blown speaker NO (would not get sound at all)

Bad Reverb UNLIKELY (controls would deselect reverb and it would be out of circuit)

Bad preamp tube NO (controls have no effect)

Bad rectifier and/or filter caps LIKELY

Bad power amp POSSIBLE

Nov 29, 2009 | Marshall Mg50dfx 50-Watt Combo Guitar...

1 Answer

Peavey 115 Low hum Low volume from input

The preamp section has a problem. It could be anything in the preamp but is OFTEN the input jack itself. They take a lot of abuse.

Also the insert jack contacts that forward the preamp to the power amp if no external FX are used can go bad.

Additional things are circuit board cracks caused by rough handling and also controls that have had the knobs mashed in which can destroy the potentiometers they are connected to.

Sep 19, 2009 | Peavey Music

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