Hum through speakers on SN AV input

It is quite common for the whole chain of components in an A/V system to create a hum loop which is very difficult to eliminate.

Does the hum go away if you turn Unity gain off?

I opted to disable unity gain in my A/V connection to my 552 and always set the Volume control on the 552 to a standard location (12.00). Then use the auto set up on my Denon A/V receiver to get the volume of all the other channels right. This allows you to get the same effect as using unity gain but helps to eliminate the hum.

regards

Geoff

Thanks for the reply Geoff

Actually i have managed to narrow it down to my subwoofer (an REL Quake). I disconnected everything all at the same time and the hum was gone.  i connected everything except the sub - still no hum. Well actually there was a slight hum still but it's only audible if you put your ear right near the speakers. With the sub reconnected the hum is much louder and clearly audible from the couch.

so - any ideas for how to get rid of the hum - is it possible to get a ground loop isolator to connect in-line on a single RCA cable?

FYI  - the sub is plugged in of a cheap extension socket connected to a wall socket on the other side of the room - not sure if that has any bearing.

Thanks!

REL subs have two inputs.

One is the LFE or low level input that goes to the Sub out socket n the A/V amp.

The other speaker or high level input is supposed to be connected to the speaker output terminals on a stereo amp ( 2 off + and 1 off -). I assume you are using both inputs.

With Naim amps it is best to connect at the terminals on the back of the speakers instead. I also found that it was better to just attach the two [+] connections one to each speaker + and to connect the single [-] return to the earthing terminal on the back of my 552. I don't know if the SN has one but if so you could try that. In any case you will get hum if you don't have all 3 connections for the speaker level input properly made.

regards

Geoff

Hi Geoff - thanks. Actually i am connecting the sub only with the low level LFE channel from the AV amp, i'm not using the speaker level connection at all.

Regards

Dan

Then I guess it must be a hum loop caused by the SONY -REL connection.Unusual that.

I don't know what to suggest other than trying a ground loop isolator. 

I am only guessing but is the SONY double insulated ( has no earth pin in the power socket on the back) and are you sure of the earth connection on the plug block powering the REL?.

If you listen at the REL is that where the hum sound is or is it at the speakers? If at the REL it might just be a dodgy interconnect with intermittent connection.

regards

Geoff

Hi Geoff - it's definitely the stereo speakers where the hum is coming from.  You were right to question the earthing on the mains block that the sub was connected to - I was experimenting and by bypassing that and plugging the sub straight in to the wall the hum has been mostly eliminated.

I'm not sure my solution is going to be very popular though - we have a lack of sockets in our lounge and by taking the extension lead out of the equation we've now lost 2 lamps in the room. better than having the hum though 

I'm just thinking through all the possible permutations of layout and mains connection to try and come up with something acceptable to the Mrs. I think i need some new sockets installed.

cheers for your advice.

It's a little confusing because the hum seems to vary from session to session even when I'm not making any setup changes. I concluded by having the sub plugged straight in to the wall it did reduce the hum, but not eliminate it.

In the end I returned everything to the way it was because losing the extension lead (that was plugged in to the socket i moved the sub to) and the lights hanging off it was not domestically acceptable.

I was recommended by a dealer yesterday to simply try a different interconnect between the av amp and the SN. I swapped the chord (cobra 3 I think) phono to DIN interconnect for a QED reference phono to phono and indeed the hum is reduced - to a slightly greater degree than changing to sub mains arrangements achieved. I can still hear it from my seat when everything is quiet, but only just.

I also ordered a stereo phono male to phono female ground loop isolator from eBay for the sum of £4, so when that arrives I'll try that both on the sub and on the main L&R preouts from the av amp, although I'm a little concerned that it will be detrimental to quality.

I use a pair of isolators between my Denon AVR4800 and 552.  The hum is gone.

Nick

Ok thanks Nick, I'll wait until the isolator arrives and see what that does.

Out of interest, what make is the isolator that you use, and have you found any adverse effect on sound quality?

Radio Shack @ $17.  I needed two because I connect both in and out.  My AVR is the hub of my whole-house system.  I have not done extensive testing, but did not notice a change when I added these.  I asked a similar question on the Forum at the time; nobody commented either way.  

I did stumble on a thread or two advocating disconnecting ALL sources not in use, for optimal performance, regardless of whether or not you have any issues.  Whenever I do a tear-down I experiment a little:  I have not heard a compelling benefit from having only one source connected (but I was hoping I wouldn't.    )

I was able to eliminate all hum by disconnecting Cable-TV where it enters my house.  My Naim dealer suggested having Comcast fix their issue.  Their tech improved earthing and eliminated 90% of the hum, and the benefit varried over the course of a day from 100% fixed to not so good.  I still needed the isolators to attain reliable silence.

Let us know what your tests reveal.

Good luck.

Nick

Received and installed the ground loop isolator today - hum totally gone.  Didnt get the chance for a proper session so will asses whether there is any impact to SQ over the coming days.

Hi DT79. Can you give us your final thoughts on the ground loop isolator? Any effect on sound quality?

thanks

Deniz

I don't think it's had any effect on SQ, I haven't done an a/b, but I have largely forgotten that's it's there, so if there is any effect then it's negligible.

Thanks. Went ahead and hooked one up myself, can't tell the difference. A very slight hum remains but is largely below hearing threshold.

I have had success using a cheaper interconnect from ebay (Gotham phone to DIN). Does nnot seem to affect sound on the surrround system and has no impact on the naim only stereo system. Sometimes a longer interconnect will kill impedence induced hum like this.