Intermittent hum issue with Frontman 15G

[longshot]

I recently purchased a second hand Frontman 15G amp and it has been working OK.

However, from time to time it will just start humming, even without anything plugged in and then after a while the hum will dissappear.

The hum is not affected by volume or tone controls, however, if I touch both the AUX input sockets and the metal part of the handle bar the hum goeas away. Touching the input socket and the handle bar does not affect the hum - only the AUX.

I've opened the case and inspected the PCB but could not notice any cracked solder or any other issue with components including filter capacitors. The metal part of the handle bar is connected to the earth connection of the AC socket via heat sink, so it looks like some problem with the ground.

Any ideas on what is causing this issue and how to fix it?

[Krwkka]

Mysterious noises that start and stop like this for no apparent reason can be caused by appliances or dimmer switches for lights. The next time it happens see if you can find out what else is happening in your house / apt. Of course, if you're in an apartment it might be a bit difficult to track down.


_

[JHow]

I had the experience the other day or putting together a tiny lm386 circuit and when I fired it up (battery power) I had 60 hz hum, which was odd. I decided not to fool with it anymore, I was tired, so I flipped off the soldering iron - and the hum stopped.

[Krwkka]

! ! !

[longshot]

I don't think it is another appliance as I live in a house and did not see any dependencies between the hum and switching on or off other electrical devices in the house. Today I switched the amp on with nothing connected to it and it started humming strait away so I took my multimeter and measured approximately 1.5V-3V AC between the AUX input ground and the metal handle (earth); 0.7V-1.5V AC between the guitar input ground and the metal handle and 0.7V-1.5V between the AUX input ground and guitar input ground. Then I took a piece of wire and a 100nF capacitor and connected the capacitor between the AUX ground and the metal handle - the hum completely dissappeared but it appeared again as soon as I removed the capacitor. I waited for few minutes but the hum was still there, so I switched the amp off and on again - and the hum dissappeared! I think this proves the there is no external appliance that causes the issue - most likely some internal component. Any ideas?

[gomez63]

It could be the aux jacks are dirty and/or need cleaning or replacing. These jacks are poor quality....