Bought a poweramp off the forums...and have some problems :(

[Smurfin]

hi all

Wonder if anyone can give me some advice please? A few weeks ago I bought a Rotel 985 mkI 5 channel, THX power amp from the classifieds. Unfortunately I needed longer interconnects than those that came with it, so it wasn't until 2 weeks after I'd received the amp that I got to try it out properly.

I've bought some good quality Belden interconnects, and have hooked them up from the poweramp to the pre-outs on my Pioneer AX5i. The problem I have is a low level - but distinctly audible - buzz/humming sound. The noise is constant unless the AX5i is switched off, in which case the humming changes slightly, but is still there. Only when the poweramp itself is switched off does the humming completely stop (as you would expect). The buzzing is also audible in EVERY channel.

The possible causes could be:

* The AX5i is the problem, and is introducing noise into the chain.
* The interconnects are the problem
* The poweramp is the problem
* It's a simple mains issue

I don't believe it's the AX5i as previously I had active monitors hooked up to it via the pre-outs, and there was no hum/buzzing at all, regardless of what power sockets in the room were used.

I don't believe it's the interconnects as this morning I've tried a couple of others and the hum has not changed or disappeared

The most obvious answer is a mains issue, but then I've previously had 5 powerful active monitors in my room and there's not been ANY issues with hum (but I don't know if this means that other kit should be fine also).

Which leads me to believe that the problem lies within the power amp. But what exactly could the problem be? Is there a way round it? Has anyone come across this before?

Advice would be appreciated, because as of this morning I've removed the poweramp from my system....I really can't cope with that buzz

I would add that the guy who sold me the poweramp has been helpful so far, and this post isn't intended to get a refund of the money I paid. I just want the poweramp to work

Cheers
Matt

[Parmenion]

Try plugging the poweramp into the same socket as the Pioneer.

regards

Parmenion

[Smurfin]

Originally Posted by Parmenion

Try plugging the poweramp into the same socket as the Pioneer.

regards

Parmenion

Maybe I'm being stupid, but what exactly do you mean?

[Parmenion]

If you have twin sockets on the wall, make sure that the Pioneer is plugged into, say, the left one and the Rotel is plugged into the right one.

regards

Parmenion

[Mark Grant]

Hello Matt,

Do you have anything connected to the AV amp that is connected to a satellite dish or TV aerial ?

I would unplug the interconnects from power amp, power the rotel up and see if it still buzzes with no inputs, just speakers connected.

If that cures it, unplug everything from the AX5i, just leaving the interconnects to power amp and power of course.

Add cables one at a time until you find what causes the buzz, which I guess is a ground loop/problem.

A process of elimination.

Good luck !

Mark.

[Parmenion]

I agree, sounds like a ground loop problem to me too.

Don't forget my suggestion for a 'quick fix'.

regards

Parmenion

[Smurfin]

Originally Posted by Mark Grant

Hello Matt,

Do you have anything connected to the AV amp that is connected to a satellite dish or TV aerial ?

I would unplug the interconnects from power amp, power the rotel up and see if it still buzzes with no inputs, just speakers connected.

If that cures it, unplug everything from the AX5i, just leaving the interconnects to power amp and power of course.

Add cables one at a time until you find what causes the buzz, which I guess is a ground loop/problem.

A process of elimination.

Good luck !

Mark.

Thanks Mark. I've disconnected the interconnects from the power amp, switched it on...and the buzz has gone. As soon as I plug in the interconnects, the buzz returns, and this is regardless of whichever interconnect I use (tried 2 different brands).

So where do I go from here? Could it be the pre-outs from my AX5i (despite not having a problem previously with actives connected via the pre-outs), or is it the poweramp I've completely removed the poweramp from the system now as the buzz is just too annoying. I don't notice if I'm playing movies loud (although even at -5 to -10db, in very quiet scenes I can hear it), but it becomes more pronounced late in the evening as the general noise floor of the environment lowers and especially as I don't play movies quite as loud

Matt

[eviljohn2]

Seems odd. Do you know if it has a UK (50Hz) power supply or a US (60Hz) power supply?

If you're running a US power supply at the UK mains frequency it could well induce a hum like this.

[Smurfin]

It's a UK one.

[eviljohn2]

Right. It could be an earth loop between the 2 units. Get some loose wire and attach it to the power amps chassis (with it all plugged and humming), case screws are good for binding these down. Now try touching the other end of the wire to your other pieces of equipment, if that cures it then attach the flying lead to the chassis of that piece of equipment.

If that doesn't work, it might be worth looking at how the appliances are earthed. You may not have had a problem with your Blue Sky's as they probably weren't actually earthed to the mains so "shared" whatever potential your Pio used as earth.

[Smurfin]

Originally Posted by eviljohn2

Right. It could be an earth loop between the 2 units. Get some loose wire and attach it to the power amps chassis (with it all plugged and humming), case screws are good for binding these down. Now try touching the other end of the wire to your other pieces of equipment, if that cures it then attach the flying lead to the chassis of that piece of equipment.

Cheers, will try that

If that doesn't work, it might be worth looking at how the appliances are earthed. You may not have had a problem with your Blue Sky's as they probably weren't actually earthed to the mains so "shared" whatever potential your Pio used as earth.

Hmm I didn't understand that part

[Mark Grant]

Hello Matt,

I would disconnect all inputs to the pioneer AX5i, just connecting the preouts to the power amp. all other sockets not connected to anything.

If no buzzing with this, add inputs one at a time to the AX5i and see what causes it.

Often caused by a cable from a sky box or freeview box, as these are usually not earthed devices, but the dish or aerial can have a little bit of earth reading on the cable, as is fixed to the chimney or gable end of the house etc.


Mark.

[eviljohn2]

Originally Posted by Smurfin

Hmm I didn't understand that part

Not to worry, suffice to say that not everything you plug into the wall actually uses an electrical earth. Older or powerful equipment usually does (like your power amps) whilst smaller bits (like your speakers) usually don't. If the flying lead technique works then you needn't worry!

Good luck with it otherwise Matt.

[avanzato]

Do the interconnects go anywhere near a power cable or power supply?
My experience has been that with earth loops I got 'hum' and with power cable interferance I got 'buzz'.

[GaryG]

If it's a ground loop problem, use the power amp as the main 'earth' and disconnect the earth lead in the mains plug on the equipment you connect to the the power amp leaving the interconnects to provide the earth via the power amp.