AV Processor / Power Amplifier Noise?

[admin_exported]

Morning
I've just installed a significant upgrade to my home cinema system:

• Processor - Outlaw Audio 950 - imported from US and running through a step down mains transformer
• Power Amp - Audiolab 8000 X7
• Front Speakers - ProAc Response 1.5
• Centre - Mission? (waiting for ProAc Response to arrive

I've got everything wired up. SQ is amazing - really transparent and detailed. But unfortunately there is a problem with system noise - significant humming.

I want to bi-amp my Proac speakers from the Audiolab power amplifier, but the amp doesn't have the ability to allow a single RCA in to power more than one channel.

I bought a couple of budget fly leads to split the signal which are just doing the job until I get my proper splitter and better quality cables

The more worrying thing though is that I'm having a problem with hum - I didn't notice it when I first got everything wired up but when I went to put the processor and amp under the TV (on a dedicated Soundstyle unit) the hum has got much worse.

Originally I unplugged the front speaker budget leads and then noise stopped but this morning there was a little bit of hum coming through the centre speaker too, even though I'm using a pretty good interconnect to link the processor and amp.

Any ideas? I wonder whether the voltage conversion is causing hum to get into the system? But it's such a pain when the sound quality is so good!

Many thanks

Steve

 

[Andrew Everard]

Could be the transformer, could be interference from the TV, could be two cables now close together causing it. The only way to find out is to take a methodical approach, checking everything - starting with turning off and unplugging the TV to see whether that's the cause.

 

[Anonymous]

Thanks Andrew

I've started by taking the power cable out of the back of the processor - the hum definitely reduces through the speakers but it's still there. This would suggest it's a problem with the power amp?

Am I right in thinking that while there might be a tiny bit of hiss when it's switched on without any signal, there definitely shouldn't be any hum?

I've got the Audiolab set for high sensitivity switching - it remains on for 15 minutes after any signal stops and then goes into standby.

I've ordered a 3.5mm jack line to use the remote switching capability of the processor / amp.

So, I've already tried to move the power cables as far away from the signal cables as possible, but the fact that the amp is still producing humming even without any power at all going into the processor?

I've never had problems like this with my audio in the lounge, although I did have lots of problems with ground loops in my pc system which runs the rest of the house.

Arrgggghhhh!

Thanks

Steve

 

[Anonymous]

Hello, it can be a little tricky to put your finger on (so to speak), but I would suspect mains borne interference. The 1st thing to do is check that you have good grounding on ALL your equipment. Ground looping is a classic cause of hum! What also is plugged in on your ring circuit could cause problems, you can isolate from this by buying a Tacima 6 way block (£20) and plugging every thing through it. If this doesn't solve the problem you could have a noisy step down transformer which needs cleaning up. As Andrew says keep all the mains cables apart from signal ones, (also from each other!) check all plugs for good, clean connections, cleaning the pins up whilst you are at it. Good luck

 

[Anonymous]

Morning

Many thanks for the replies.

Well, it certainly does appear to be mains borne interference. Even when I unplugged the processor, I was still getting hum through the amplifier. When I unplugged the transformer, the hum reduced further, but the biggest culprit was the power supply for the X-box 360 - the interconnect cables were running right over the top of the power supply and when I unplugged it, the hum virtually disappear. Finally, I unplugged the TV, and no hum!

So then what I did was allowed all of the signal and speaker cables to remain on the floor behind the Soundstyle TV unit, but manually raise (temporarily onto the top of the TV) all of the power supplies and mains cables.

Bingo - the hum has disappeared and I'm left with very clean sound from the speakers, with just a small amount of hiss when no signal is present (I assume this is perfectly acceptable) I will build a small shelf on the wall behind the TV to place all of the power supplies and then use cable ties to keep all of the cables running well above the signal and speaker cables.

I hadn't realised that the RCA cables would be so responsible for inducing hum into the power amp. I've just ordered a couple of Gotham GAC-1 cables to replace the budget leads that are currently bi-amping the front speakers.

Are there domestic RCA cables which are better at resisting this type of interference?

Best wishes

Steve

 

[Anonymous]

Am pleased that it's been easy to sort out. Russ Andrews Powercords are excellent at cutting out the RF interference off the mains, I have been using them for years. I find most people do not realise the substantial improvements to be gained to the music by cleaning up the mains.

All the best

Trevor

 

[Andrew Everard]

Glad you've sorted it - these problems can often be sorted by careful cable-dressing, eg ensuring that signal cables and mains cables always cross at something like right angles, rather than running alongside each other.

 

[professorhat]

Where's Masterbluster to suggest the OP must be wrong after his testing. After all, changing power cables can't make any difference, remember...