[grazy]

Hi All,

I think bad luck comes in threes! This being my third and hopefully final plea for help for a while!

I have just got myself a nice custom made AV cabinet from Blok UK and loaded all my equipment into it! Only when I power it up I get a Hum in the right channel of my 2 channel amp! (RB-991)

I have a Rotel RSP-1068 (had problems with this but now ok) and a second power amp (3 channel RB-993).

If I turn the Processor off the hum is still in the right channel? If I turn the power amp off and on or leave it for a while the hum does go?

I'm assuming if it was a ground loop issue it would occur on both channels? with the processor being off I guess I can elimate the phonos connected?

I'll double check the speaker cables tonight, any other ideas? I only had is all disconnected and i may have put it on the side with a slight thump and assume i havent ruined something inside? I also gave it a wipe to remove some dust so not sure i have done anything too significant to cause this problem?

hope someone can help. I will of course try getting in contact with Rotel too!

[Mark.Yudkin]

Originally Posted by grazy

If I turn the Processor off the hum is still in the right channel. If I turn the power amp off and on or leave it for a while the hum does go.

I'm assuming if it was a ground loop issue it would occur on both channels?

Yes.

Originally Posted by grazy

with the processor being off I guess I can eliminate the phonos connected?

Not necessarily. However you also said the hum goes if you leave it on for a while, and that means you can probably eliminate the phono connections. That said, I strongly recommend pressing hard on all phono connections for the right channels on all devices you own, just to be absolutely sure. I've had an intermittent hum on a subwoofer that was caused by the subwoofer cable not having been pressed in hard enough after a reorganization.

Originally Posted by grazy

I only had is all disconnected and i may have put it on the side with a slight thump and assume i havent ruined something inside? I also gave it a wipe to remove some dust so not sure i have done anything too significant to cause this problem?

If it isn't a loose connection, your next course of action is to send it in to Rotel through your dealer.

[Slang]

If your connecting through a balance cable , try replacing this one cable OR try disconnecting all cables and see if the hum still there , if still hum , amp. problem ! Hope this helps !

Larry

[grazy]

I'm very confused now! I have just swapped my 2 channel and 3 channel amps over in the new cabinet. and the phono leads I'm using only really reach as the are so swapped them over on the back of the processor. My 2 channel now seems ok. I get a slight hiss as normal but my 3 channel had a relatively loud hum on the left channel? If i wiggle the phono it went away so then i thought it must be the phono cable.

I changed the cable for a cheaper one just to test my theory and yes loud hum gone, but if i put my ear up to the speakers i can hear the hum and like i say the 2 channel amp just hisses. This is happening with or without (in standby) the processor turned on. And the hum is in all three speakers.

The only other thing that has changed in the multi-adaptor the amp was plugged into so I tried extending it to another room, still get hum. found a longer cable on my computer so tried this and plugged in where it was before! and yes hum is back! Starting to wonder if the minor hum has always been there on the 3 channel amp?

Pulled all three phonos out the back and no hum! so its starting to sound like a ground loop hum but only on the 3 channel amp? anyone got any ideas? could other cables behind the TV cause this? if too close together?

will this hum ruin the amp etc? guessing not? it does seem to be the other amp now?

Thinking the original hum was the phono, maybe it was shorting inside slightly? I have tighten everything up on that cable and put it back in now

the two channel amp has an un-attachable plug where as the 3 channel has a push in cable.

hope I'm explaining this right! if anyone can make sense of any of my dribble please post your thoughts!

Graham

update: I tried unplugging the rear left and right. this removes the hum from those channels but not the centre which is still plugged in. This was done when the processor is on standby!

am i being paranoid? The only reason I'm concerned is i hadn't noticed it before and the two channel amp doesn't do it?

[Mark.Yudkin]

A hum you can only hear when you place your ear on the speaker but not when under normal circumstances is probably something you can ignore as both harmless and basically inaudible.

Your first post stated that the hum was on one channel only. Your latest post suggests a ground loop with the 3 channel amp, indicating in the update that you have a hum in all three channels. This distinction -. one channel or all channels - is of course highly significant. A ground loop would affect all three channels indiscriminately, a bad cable or inadequate connection will affect only its channel.

To resolve the hum we need to diagnosis the cause. Disconnect all PC or PC-like devices (laptops, media players). Also disconnect all aerial leads (TV, freeview, cable, satellite, radio) from the back of all equipment, so that there is no way you can watch or listen to any broadcasts. Does that eliminate the hum? If so, reconnect one-by-one until the hum reappears, until you have found a minimal hum-free setup and post back with the configuration and we can take it from there. If removing PCs and TV feeds doesn't help, strip the system down to total disconnectivity and reconnect piecemeal until you have the minimal hum-free setup and post back. This is best done when the children are in bed, as the language this will provoke will not be suitable for minors.

[grazy]

Thanks Mark! This issue has evolved somewhat! so will have a look over the next few days! I don't have any analogue devices plugged into the processor directly only optical and coaxial.

and like i say it only affects the 3 channel amp now and not the two channel connected to the same processor!

[MarkLG]

Sounds like a ground loop problem. I've just spent a bit of time getting rid of a background hum after putting a new amp into my system. Tracked it down to my TV, which was creating some sort grounding problem via the HDMI connection to the processor.
Plugging the TV into a different multigang extension from the rest of my AV kit has removed the hum.

[grazy]

I'll try unplugging things tonight but like i said I would have thought both Amps 2/3 channel would do the same?

The processor is relatively old and using optical/coaxial so not sure the Ground loop hum with be transmitted this way?

Oddly the hum is still there even in a different socket! and even if the proceesor is turned off at the wall! but this being the only thing the amp is connected to must be the problem but why its on the 3 channel I just dont get!

I'm guessing the 3 channels are independant? so when removing 1 or 2 of the phonos it only removes the hum on those channels?

[grazy]

Sorted! well I have found the culprit! I have a AC RYAN media player/streamer connected via coaxial (worse player ever DO NOT BUY ONE!). I unplugged the coaxial and the hum is gone!

Has anyone got a suggestion on how I stop the media player from doing this? Do i need to earth it or stop it from earthing?

[Mark.Yudkin]

Originally Posted by grazy

Sorted! well I have found the culprit! I have a AC RYAN media player/streamer connected via coaxial (worse player ever DO NOT BUY ONE!). I unplugged the coaxial and the hum is gone!

Has anyone got a suggestion on how I stop the media player from doing this? Do i need to earth it or stop it from earthing?

Unfortunately, you probably can't stop such a device (you admit yourself - IN CAPITALS), so you need to isolate it. Whilst fiddling around with earthing might remove a hum, it also might end up burning the house down or electrocuting members of the family - so don't even consider such dangerous actions. Especially as the fix is trivial.

If the media player has an optical output, use that. The optical cable acts to break the electrical ground loop.

If not, get yourself a simple coax - optical convertor such as this or this.

[grazy]

The main reason I went for it was because it had coaxial! As i only have 2 opticals on my processor! I do have 3 coaxials though. I'm already usng a switcher on one of my optical inputs!


Seeing as I don't use it that often I guess I can just use it via the TV optical out for now. The only down side being the TV has to be left on and any more complex signals from films etc would require the direct connection!

I'm happy enough I found the problem! thanks all for your help!

[Mark.Yudkin]

Originally Posted by grazy

The main reason I went for it was because it had coaxial!

The reason most such devices don't have coax connectons is because if they did, they'd cause the woes you're experiencing. So the manufacturers of these noisy, dirty devices stick to optical connections so you won't realize just how bad they are.

Although automatic active optical switches aren't cheap, a remote controlled switch is affordable.

[MI55ION]

Originally Posted by Mark.Yudkin

The reason most such devices don't have coax connectons is because if they did, they'd cause the woes you're experiencing. So the manufacturers of these noisy, dirty devices stick to optical connections so you won't realize just how bad they are.

Although automatic active optical switches aren't cheap, a remote controlled switch is affordable.

I actually own one of these dirty devices Mark, using HDMI and coaxial with no issues. Lol.

Agreed about staying away from it though, the user interface is too clunky for my liking. Perhaps the Dune media players are a better buy, at double the price they better be!

[Mark.Yudkin]

Originally Posted by MI55ION

I actually own one of these dirty devices Mark, using HDMI and coaxial with no issues. Lol.

Agreed about staying away from it though, the user interface is too clunky for my liking. Perhaps the Dune media players are a better buy, at double the price they better be!

The OP also had no problems before his new amplifier. Just because a device is designed to cause problems doesn't mean it is guaranteed to do so. There will always be the exception, so count yourself fortunate that you're one of them.

[noiseboy72]

You can get hum blockers / earth lifts for Co-ax digital connections, as you are not the first person to have this issue. They use opto-isolators, so are not cheap. You could try a cheaper transformer based video hum-bucker designed for CCTV systems. I pressed one of these into service on a gig once and it did work, as it has more than sufficent bandwidth, but no promises it would work in your situation.

Hum loops on unbalanced systems can affect just one channel in some circumstances if the internal architecture is a monoblock construction. Internal earthing and board layout can make one channel more susceptible. Domestic amps tend to have quite high input impedances and this seems to increase the noise floor into the bargain. Induced hum is usually more of an issue, but good cable management normally cures or reduces the issue.