Problem with loud buzzing noise on amplifier

Thank you very much for responding. With regards to the noise, it appears to be coming from the speakers, however we're pretty sure the problem is with the amp/preamp because we connected the amp to another sound system with different components and the noise continued to occur. Also, the output transitors were replaced only on one channel since they were functioning properly on the other channel.

Sounds like it needs to go back to Audio Plus Services.

This sounds like the amplifier could be oscillating. Its not likely to be a transformer problem- that would not damage output transistors.

I would get the amplifier to a reliable service department or the manufacturer. If you don't attend to it, the transistors could well fail again.

If there really is an oscillation, its at a very high (inaudible) frequency, and the buzz you hear is merely an artifact. An oscillation like this can damage output sections as it forces the output transistors to switch very quickly. This can overheat them quite easily.