Buzzing from stereo amplifier, is it faulty?

[sadbuttrue]

Disclaimer: I'm a complete AV noob, so may not know what I'm talking about

I recently purchased a second hand stereo amp (Denon PMA-355) for light use. With nothing but a set of speakers connected the amp generates a kind of buzz, which modulates about 4 times as the volume is increased. This can also be heard quite prominently via the headphone socket and is very annoying. Is it simply a faulty component that could be repaired by someone qualified?

Any help appreciated.

[mr_seanstanley]

Is the buzz coming from inside the amplifier chassis or from the speakers?

[sadbuttrue]

The buzz comes from both speakers and headphones.

[mr_seanstanley]

have you got any source components connected when it makes the buzzing?

[michael orme]

Check if it needs to be earthed, and if it is, I bought an amp once, the earth lead was detached in the plug. Its worth trying before you start spending money.

[clockworks]

Have you tried it with a source component connected? You may find that the buzzing stops when you connect a CD player - the amp may be picking up interference with the inputs "floating".

[sadbuttrue]

I've tried with and without a source connected, the result is the same. I thought it could be some local interference, so have tried it in another part of the house. It has the factory fitted moulded plug, so if it needs earthing it should already be.

[clockworks]

I've had some wierd problems with buzzing/warbling noises. To get to the bottom of it, I went right round the house, unplugging or turning everything off. I also tripped all the circuit breakers, except for the one supplying the AV system.

The main problem was the LCD TV in the kitchen. On standby, it was generating interference, which was then fed throughout the house via the coax cabling. Turning it off at the main switched fixed that.

Another problem was with a power amp. I had to disconnect the cable inside the amp that connected the chassis to the earth pin on the IEC mains inlet socket. The chassis is still earthed via the phono leads to the rest of the system. Having two earth paths was causing the problem.

If you go through all these checks, and it still happens, it's probably a faulty amp. If it comes through both channels, it's probably a fault in the power supply, maybe a capacitor breaking down. Should be a simple fix for an old-fashioned TV/hifi repairman. Take it direct to the repairer, not to a shop - they'll probably double the price.

[sadbuttrue]

Thanks clockworks, I'll give your idea a try later today. Hopefully it's not something I actually need switched on or in standby causing the problem.