Question about Marshall Mg100dfx 100-Watt Combo Guitar Amplifier

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Hiss and hum: Marshall headJcm2000 dsl100. Doesn't seem as loud as it should be, and over the top hiss and hum when I crank up the volume. The amp is a floor model; about three-four years old. Could it be a tube issue?

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More than likely you have a power issue. Look closely at the main filter caps. These are the 2 larger than the other caps. They are usually about 4700uf at 63v (generic values but yours should be close). Check them for swelling, if no signs of that then you will need to due a capacitance check on them. Sometimes but not always, they will show bad on an esr meter also.

Posted on Jul 11, 2009

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I turn my fx off but can still here it and the od sound is lower than the fdx button when i push it in to turn it on


2 things 1: there is no off button for the built in digital effects, you just turn the level down to minimum, the fdx button you speak of is actually fdd (frequency dependant damping) this is supposed to mimic how a tube amp sounds

2: when you press the od switch the amp goes into hi gain mode and will hiss with no input, the point is if you plug a guitar in and play it the volume of the guitar is way above the hiss and you don't hear it

so in conclusion having bought and sold many mg series amplifiers the on you have is perfectly ok

Mar 10, 2012 | Marshall Mg15dfx 15-Watt Combo Guitar...

2 Answers

Low volume on my marshall


I am very new here and don't know how to answer a question to a specific problem so I will write about the most common problems that I have had over the decades doing guitar amp repairs. If you find that your amp is extremely low in volume and then suddenly comes back to normal- check out the effects return [or power amp in] jack. Especially in Marshall amps-these corrode and your signal dies. If there is loud noise such as hissing and crackling with no guitar patch cord in the input jack- the input jack is likely at fault. They normally have switching contacts that ground part of the input circuit when the 1/4 inch male plug is disconnected. When this in is corroded or too weak to make normal contact, you can get these symptoms. If your amp is a solid state Marshall or Fender and there is a random buzzing sound with no guitar signal connected- hit the side of the amp and listen for the buzz to go away or become louder-if it does, this usually means that the connections are loose at the two large filter capacitors. In one or more Marshall amps, they use a filter circuit in the low voltage power supple for the preamp tubes. If you encounter a dead Marshall[the model escapes me now] remove the circuit board and resolder the four connections at the bottom of the bridge rectifier. If you have any other amplifier repair questions you can email me direct at computerlen@hotmail.com.

Nov 14, 2011 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

I have a very loud hiss/buzz sound coming from my Roland. It goes away if I lower the high volume knob. This just starred to happen recently. I tried changing connections from ch1-4 but no fix.


If this ties to a keyboard, make sure the keyboard and this are BOTH plugged into the same receptacle. You should send a higher level from the keyboard (turn volume up to around 70% or so) and use less volume at the input gain of this amp. Use more at master volume if the amp has one if needed. If the hiss is there with NO input cables plugged in and input gains at 50%, that is objectionable, the amp probably needs servicing. Unused channel gains should be clear down.

Apr 11, 2011 | Roland Elektronische Musikinstrumente...

2 Answers

Marshall Mg 100DFX power on no sound it just cut out last time i played it.The fan has issues I wonder if there is a cooling sensor shutting down the amp output.I thought solid state amps were bullet...


Something has probably failed or become a bad joint. If you turn up the gains and volume to max is there any hiss or hum from the speaker? If not there will be a problem in the power amp or power supply. Check fuses at back. The speaker may be open circuit too, that is easy to check with a multimeter. If you can't get far yourself, you'll need a repairman.

Solid state amps are not that reliable these days, there are so many things that can fail due to all the effects that people demand to be built in. Look at how many people are reporting problems with ss amps here.

Apr 02, 2011 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

Marshall MG100HDFX, VERY loud painful humming/noises as soon as the amp is turned on. Cant be adjusted by volume or anything, is this a connection problem?


Likely the filter capacitor(s) have failed OR the power amp has shorted driving DC with ripple into your speaker (very bad). Take it for repair before damage might be done.

Jan 10, 2011 | Marshall MG100HDFX 100-Watt Amplifier Head

1 Answer

My swr workiongpro 15 suddenly has a very noticable hiss even when the amp is muted, and when I play the high end is more prominent than it was before.


If you are having the treble/high turned up there will be hiss. This is due to the statistical noise in electronics, including semiconductors. It is a matter of degree. The hiss should be 30 Db below your program level or so.

It is very common for one to change settings and suddenly start to notice hiss or hum at certain settings.

IF YOU CAN, go to a music store and COMPARE the amp to yours at the same setting with NOTHING plugged in. (cables and guitars can generate hiss or other noise themselves).

There is very little in your amp that would have changed to suddenly start generating hiss, so FIRST compare. This will minimize the chance of spending money at a shop to be told it is normal.

Sep 14, 2010 | SWR WorkingPro 15 200 Watt 1x15" Bass...

1 Answer

My new mg50fx has a ton of hiss when i turn it on. anything i can do?


Make sure the master volume is turned up and the inout gain is down some.

All of the electronic devices suffer from the statistical noise within the amplifying components. Keeping the inour gain down some tends to limit the gain where the hiss is most sensitive, that is the high gain in the "front end" or preamp section.

A "ton" is not a MEANINGFUL measure of the loudness of the hiss.

A meaningful measurement would be the Db relative to the normal program material.

Test with no devices plugged into it as the preamps in guitars can create hiss too. The hiss should be barely perceptable at 5 feet from the amp.

May 04, 2010 | Marshall Mg50dfx 50-Watt Combo Guitar...

1 Answer

Technics sx-pr604 piano makes a constant loud hissing noise when on, everything else works fine. Is this hard to fix?


This could be many things. It is most likely noise from a defective chip in the unit. If sounds are normal except for the hiss, then test if the volume control reduces it. IF not, then problem is in the power amp section. If it does vary the loudness, then problem is likely between the D-A convertor and the volume control.

I would first try to isolate this by cooling selected parts with circuit cooler mist to see if you can find one that reduces the hiss when you cool it... Spray, then wait ten seconds before moving to the next on.

USUALLY semiconductors cause this, but rarely a bad resistor or cap can as well.

Mar 29, 2010 | Music

1 Answer

Hiss in new fender frontman 65R. Can't seem to dial it out in either input.


A certain amount of "hiss" is present in electronic amps due to the statistical noise in electronics.

The hiss should be WELL below the level you get when playing. If you put you ear to the speaker, expect to hear some hiss with nothing plugged in. Ten feet away it should be very faint.

Dec 30, 2009 | Fender Music

1 Answer

Constant buzzing in my 15 W amplifier


Make sure you have a ground prong on your power cord. Most input jacks nowadays are closed circuit. They have a switch built in that won't allow any sound without the cord plugged in. You may have a damaged jack that will give you a loud hiss, a loud hum or crackling depending on what volume your controls are set at.

Aug 27, 2009 | Line 6 Spider Iii 15 Modeling Guitar...

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