Hum when using Cyrus One as amp for Centre with Yamaha DSP E800

[bighairy]

I've been using my old Mission Cyrus One amp to power my main speakers for my home cinema for a while, with (recently added) a Yamaha DSP-E800 to decode.

I just picked up a second hand Cyrus with the idea of using it as a power amp to drive my centre: I was able to detect quite clear tonal differences between my Cyrus One and the amp in the Yamaha processor.

However, when I connect the new amp to the centre channel output of the Yam, I get a hum (sounds like mains hum) when I turn up the volume of the new amp. The new amp is clean and doesn't hum with any other source.

I've tried many sets of cable. I've tried plugging the new amp into a power socket as close to my original Cyrus (not easy as everything is behind a big wall unit) but that didn't help. Annoyingly, if I take the centre output from the Yam and feed it into my original Cyrus it sounds perfect and comes out at a similar level to the main left and right outputs.

Do I have some sort of earth loop? What could be causing this? I've sort of got round the problem by playing with relative levels to minimise the hum, but it is still there.

Any suggestions would be appreciated!

graeme

[Radioactive__Man]

I would suggest you need a power amp, not an integrated one.

You wiil no doubt be setting the Cyrus volume quite low and attenuating the volume via the Yamaha.

This is not the proper amp for what you are doing with the centre channel output, see if you can pick up a 2nd hand Cyrus XPA power amp.

Your Cyrus connected to the centre output is amplifying the distortion from the Yamaha through it's pre-amp stage !

[bighairy]

Originally posted by Radioactive__Man:
<STRONG>I would suggest you need a power amp, not an integrated one.
!</STRONG>

I understand the difference between an integrated amp and a power amp but I guess what I'm asking is why is there a difference between the main outputs and the centre output on the Yamaha. My other integrated amp works fine taking a feed from the main outputs but the new one has a hum (but only when connected to the Yamaha).

graeme

[Jas]

You should find that your cyrus amp is on a mains detachable lead and that your amp has 3 pin connectors. disconnect the earth cable from the mains plug and just watch that hum disapear when you reconnect the mains plug to the amp and the mains.
The problem lies in the fact that the yam (notice that you yam only uses 2 core mains cable & your cyrus uses 3 core mains cable)uses a internal star earth and your cyrus amp uses a mains based earth the two are incompatable and create an artifical earth loop. i had the same problem using my pre outs from my denon when connecting to my meridian mono block power amps.The above solved my problem and should solve yours.
E- ME if you have any more problems and best of luck Jas.

[bighairy]

Fantastic! Earth taken out at the plug and hum is gone. Thanks! At least I know I have an RCD to protect me if anything goes wrong inside the amp :-)