Question Need help with humming through front speakers

PaulMancUK

Novice Member
Hi, I hope I am posting in the correct section. I have a Yamaha Aventage A1010 av amp that I am running in 5.1. I have taken the front left and right pre-outs and put them into a Roksan K2 intergrated amp to drive my fronts. This works well for me because I can use my cd player directly plugged into the the roksan.

The problem I have is the hum that I hear though the speakers when I use the yamaha av amp. I don't get this hum when I use the roksan on its own.

What I have discovered is that the hum only appears when the tv is turned on. If the tv is turned off but a dvd player is running or the freeview box is on, the sound that comes from the front speakers via the rosksan which comes from the av amp's pre-out fronts, has no hum. The hum only appears when the tv is then turned on and the hum only comes out of the front left and right and not any of the other speakers. I read that this is probably a ground loop and I have made sure all items are running from the same plug but it makes no difference. I have heard different hum noises and I would say this is a hum of about 60hz. I did think it was because the rca cable from the preouts of the av amp to the roksan was poor quality and not shielded enough but it is the same with more expensive cables.

The equipment all sits in a rack below the tv. Even if I disconnect the hdmi cable from the tv which goes into the av amp, the hum will still be there with the tv sitting in issolation and switched on.

I am not sure of where to start fixing this. Do I need some type of power filter or do I just need some sort of filter for the rca cable from the av amp to the roksan?

Any information would be much appreciated.

Thank you
 

PaulMancUK

Novice Member
A bit more information after playing around this evening.

So, av amp is connect to stereo amp via front preouts from the av amp.

Humming only occurs when the tv is on. The stereo amp - Roksan K2 has an ht bypass - does not hum on any other setting.

If you turn the tv off, the hum stops. Connected to the tv is a uhf cable which comes from the freeview bt box, satalite cable which comes from the humax freesat and the hdmi cable that comes from the av amp. removing and putting back all cables has an effect on the hum to some degree.

I have tied connecting up the earth screws on the back of the amps with a wire (the type you get to connect a phono earth and made no difference either.

I don't understand how earthing works but I am starting to think that the rca cables from the av amp to the stereo ht bypass amp need to have a filter? This situation is driving me mad!
 

noiseboy72

Distinguished Member
It certainly sounds like the TV is causing the problem, as they quite commonly connect the audio ground as a functional earth and this then gets transmitted through to other equipment.

I think you will need to break the ground path to the Roksan amp. You can get them from £10 or so if you wanted to try and see if it cures the problem, but it's worth buying a more expensive one if it fixes the issue. This -https://www.amazon.co.uk/Oehlbach-9052-Audio-RCASeparation-Suppressor-Subwoofer/dp/B017HBBOP4/ref=sr_1_11?crid=3HIRTBAPBZMGK&keywords=ground+isolator+loop&qid=1552724597&s=gateway&sprefix=ground+is%2Caps%2C133&sr=8-11 would be OK.
 

PaulMancUK

Novice Member
Thanks. I have just ordered a cheapie to see if it has any effect. Fingers crossed it does the job and I can look at a better filter for a longer term solution.
 

Rambles

Distinguished Member

PaulMancUK

Novice Member
It certainly sounds like the TV is causing the problem, as they quite commonly connect the audio ground as a functional earth and this then gets transmitted through to other equipment.

I think you will need to break the ground path to the Roksan amp. You can get them from £10 or so if you wanted to try and see if it cures the problem, but it's worth buying a more expensive one if it fixes the issue. This -https://www.amazon.co.uk/Oehlbach-9052-Audio-RCASeparation-Suppressor-Subwoofer/dp/B017HBBOP4/ref=sr_1_11?crid=3HIRTBAPBZMGK&keywords=ground+isolator+loop&qid=1552724597&s=gateway&sprefix=ground+is%2Caps%2C133&sr=8-11 would be OK.
Hi, I managed to get a cheap av:link ground loop isolator today and it has stopped the hum completely. I cost less than £10. I was wondering how more expensive ones differ from this if it has stopped the hum and still sounds good? Any further info much appreciated. Thanks
By the way, I was just reading the reviews on the product I bought at one person said this - These transformers are THE low cost solution to solving hum problems due shared grouds between your audio equipment. I bought one just to see how good it was, thinking it can't be that great for price. I was happily wrong! Using an audio analyzer I measured the following:

Frequency Response -0.66 to +0.60dB from 20Hz to 20KHz
THD 0.0054%
Stereo Crosstalk -96.8dB

I was so impressed I bought another one.

PS: I noticed another reviewer complained of loss of bass and volume. I found no evidence of that at all. I did my testing using a typical load impedance of 10k ohms. This was the input jack on my my PC soundcard.

Do you think I am going to hear any big differences going for something expensive. I have only watched tv with the new isolator tongight and it was pleasant not to hear any hum. I didn't notice any difference to the sound quality but there again if it is slight you can only tell by swapping back and forth. The info provided about does not mean that much to me but you may be able to give an opinion on it? Many thanks
 
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PaulMancUK

Novice Member
It was someone that had written a review that had tested it and made that statement. I have had a chance to listen more today and, although I have no equipment to make measurements and wouldn't understand them all anyway, I do recognise that the sound is now missing frequency ranges. The sound is clear but it sounds 'thin' and lacks any bass. So, I guess what I need to do now, is find out if more expensive versions keep all the original frequencies in otherwise it will be pointless paying for something more expensive. This is a completely new area to me, so any advice would be much appreciated. If these little gadgets always knock off some frequencies, do that mean you would have to go for something like a main conditioner maybe? Who knows.
 

noiseboy72

Distinguished Member
These transformer based isolators are very dependent upon the electronics feeding and being fed by the isolators. Poor drive ability or a low input impedance will affect the bandwidth of the signal, so this may be the effect others report. The quality of the transformer itself will also make a difference.
 

PaulMancUK

Novice Member
I have been having a better listen today noiseboy72 and I realise the cheap isolator has bad the sound 'thin' and lacking in bass. Disconnecting the earth from the tv power cable got rid of the hum but I don't think this would be safe. The Roksan K2 amp that is being used for the fronts - I notice has a power lead that includes an earth. It has only just dawned on me that I had no problems with a NAD amp running the fronts because it doesn't have a seperate earth. I am guessing the hum would have gone if I disconnect the earth wire from the power lead on the Roksan K2 also.

In these situations, do you know if the best solution is to always put in an audio line isolator rather than mess with earths?

Also you recommended the Oehlbach 9052 Audio Linear 8. Do you know if this will left a full set of frequencies through? Would this give me the same quality rca signal I would have got without the filter and my tv switched off to stop the hum. If not, is there anything else you could recommend? Sorry for all the questions. Really appreciate your advice on this. Many thanks
 

noiseboy72

Distinguished Member
No, please do not remove any earths. Think of it this way, if you remove the earth from the TV and it develops a live to case fault, then the earth path will be through the audio cables, any decoupling components within the amps and then out through the amp's earth. This might well not provide an earth path that is low enough in impedance to trip an RCD and you therefore have both an electrocution and fire risk.

A better isolating transformer will provide a more uniform response. The issue with the cheaper ones is that the cores saturate and bass in particular suffers. Try the one I linked to or the Behringer unit, linked by @Rambles. Both are likely to be a big improvement!
 

PaulMancUK

Novice Member
I have a similar problem in my set-up with a PC causing ground noise, I use a Behringer hum destroyer between the pre-outs of the AVR and the inputs of the power amp, together with 4 decent quality RCA to TRS cables, works well for me:

https://www.amazon.co.uk/Behringer-MICROHD-Hum-Destroyer-HD400/dp/B000KUD2G4

Roland Dual TRS - RCA Interconnect Cable, 3ft/1m at Gear4music
I have had some behringer stuff before and been happy with it so I decided to go with a brand that I know and it is cheaper. It arrived today and works perfectly like you said. Full range of frequencies now - well to my ear anyway. Thanks for your help.
 

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