Strange humming noise...


New member
Username: Mogwai

Post Number: 1
Registered: Mar-05

I recently bought an old Pioneer KX-333 amp/receiver at a secondhand shop.

I have my Teac record player plugged into the Phono inputs of the amp(the earth wire is also attached) but the thing is that after about 30-60 minutes a strange loud humming noise starts to come out of the one speaker. I then switch the amp off for about a minute or two and then everything is fine again for about 30-60 minutes. Very irritating!

It did this with two different sets of speakers and earphones with the same reults. It also happens when I only have my PC's sound going through the amp, so I don't think the problem is with the record player.

After messing around I realized that when the speakers and the record player are not attached to the amp and I only listen to the radio with the earphones, the humming noise did not occur.

Any ideas on what the problem could be?


J. Vigne
Unregistered guest

There is a bad capacitor in the output stages of the amplifier.


New member
Username: Mogwai

Post Number: 2
Registered: Mar-05
Okay, I don't really know that much about amps - what does a bad capacitor mean? Can I get it fixed?

Thanks for the reply.

J. Vigne
Unregistered guest

The chances are good that it can be fixed. You will have to decide how much you want to pay to fix a second hand amplifier.


Bronze Member
Username: Sexxybeast_5

Geelong, Victoria Australia

Post Number: 24
Registered: Mar-05
and it could be uve got your power wire running down the same side as your rca leeds or u avnt earthed the amp properly

Unregistered guest
If the amplifier has a continous humming noise from the time you first turn it on it is possible that a mains cable is running next to one of the input cables and the input is in a ground loop. But as you said the humming noise comes on after some time it is most likely to be a bad capacitor, because the hum is only in one speaker it is unlikely to be the electrolytic in the power supply, so it is most likely to be a coupling capacitor. A coupling capacitor blocks DC so if it is faulty, DC will be getting into parts of the amplifier where it shouldn't be.
To test a capacitor use a VOM/multimeter (volt-ohm meter) it should read "Open Circuit", "off limits" "0L" and this means the capacitor is working. A bad capacitor will read a couple of kilo-ohms. When replacing capacitors, choose a replacement with the same value OR HIGHER (never lower) and with an operating voltage the same or higher. For vacuum tube circuits, the operating voltage should be above 400V but for transistors it can be low. I usually recommend Metallised Polyester Film or Mylar capacitors.
If you do change the capacitors, they should be NON POLARIZED and can be connected either way round.
Good Luck :-)
« Previous Thread Next Thread »

Main Forums

Today's Posts

Forum Help

Follow Us