I have a hum on my amp - will that help?

[JoachimStrobel]

Hello,
i am connecting an external amp to my NAD T778 and it gives me a slight but audible hum or noise. I tried a lot, even removing the earth (it got worse), removing the antenna cable that goes into the attached cable receiver, but there was a little improvement. I came across this

Oehlbach Audio Linear 8 - Galvanic isolation filter for turntables & subwoofers - Interference suppression filter to eliminate ground loops.​

Audio Linear 8

Mit dem galvanischen Filter Audio Linear 8 werden potentielle Störfaktoren beim Anschluss sämtlicher Komponenten, wie z.B. einem Plattenspieler oder einem Subwoofer, effektiv eliminiert. Durch jahrelange Erfahrung und technologischen Vorsprung hat Oehlba…

www.oehlbach.com

Will that help? Does it change the sound? I have tried a smaller version that looks like a cable with a mounted transformer and it reduced the hiss already. Any other thoughts?

 

[sam_adams]

i am connecting an external amp to my NAD T778 and it gives me a slight but audible hum or noise.

What brand and model amplifier?

 

[JoachimStrobel]

Parasound HCA 1000, 1000A, 1200. They are all 25y old. Nad 778 Preout (Center)

 

[sam_adams]

Parasound HCA 1000, 1000A, 1200. They are all 25y old. Nad 778 Preout (Center)

All the devices are three-wire with a safety ground to the chassis. The hum is there because of a Ground Voltage Differential (GVD). That's why it gets worse when you lift the ground on one of the devices. More of the inter-chassis current flows through the shield of the interconnect making the hum worse.

From Bill Whitlock:

Fixing involves eliminating the GVD by either plugging all devices into outlets that are as close as possible to each other on the safety ground leg or tieing the chassis together with a conductor that has a lower resistance than the combined parallel resistance of all the shields on the interconnects. If neither is possible, then transformer isolation breaks the loop on the interconnects.

 

[Mr. Widget]

EDIT: sam_adams just posted a diagram of the classic ground loop.

If your problem is a ground loop issue and that is the most common cause of hum, you can try lifting the ground which you have, you can try improving the ground through various mechanical means, but the method that is typically the most successful is to use high quality isolation transformers in the audio circuit.

Jensen ISO-MAX are used in broadcast and recording studios and are absolutely top quality. https://www.jensen-transformers.com/product/ci-2rr/

 

[JoachimStrobel]

All the devices are three-wire with a safety ground to the chassis. The hum is there because of a Ground Voltage Differential (GVD). That's why it gets worse when you lift the ground on one of the devices. More of the inter-chassis current flows through the shield of the interconnect making the hum worse.

From Bill Whitlock:

View attachment 243220

Fixing involves eliminating the GVD by either plugging all devices into outlets that are as close as possible to each other on the safety ground leg or tieing the chassis together with a conductor that has a lower resistance than the combined parallel resistance of all the shields on the interconnects. If neither is possible, then transformer isolation breaks the loop on the interconnects.

Thanks for the detailed information. I will start grounding the chassis as I read that the Parasound uses chassis as ground and this is not always perfectly connected to the earth pin.

 

[antcollinet]

Thanks for the detailed information. I will start grounding the chassis as I read that the Parasound uses chassis as ground and this is not always perfectly connected to the earth pin.

Grounding the chassis won't help with a ground loop. It might even make it worse.

Regarding the device linked above - it is difficult to tell from my bad german how it works, can you describe how it is isolating?

Is it a galvanically isolated transformer? Or some other method of isolation?

EDIT - just used google on the german. It claims galvanic isolation, but with no detail on how it works. At £40 it might be worth a punt, especially if you use Amazon so you can return if it fails to work as advertised.

 

[JoachimStrobel]

It is galvanic. I realize too that amps with a real good design are less prone to hmm then others. Those Parasound, as good as they sound, always gave me trouble with noise.

 

[antcollinet]

It is galvanic. I realize too that amps with a real good design are less prone to hmm then others. Those Parasound, as good as they sound, always gave me trouble with noise.

Ground loops are a system problem, not a component problem. Any device (no matter how well designed) that is grounded to mains can have hum (or other ground noise) if it is connected to another grounded component (even through additional ungrounded components), and somewhere between the two is an unbalanced analogue connection.

 

[Ken Tajalli]

Hello,
i am connecting an external amp to my NAD T778 and it gives me a slight but audible hum or noise. I tried a lot, even removing the earth (it got worse), removing the antenna cable that goes into the attached cable receiver, but there was a little improvement. I came across this

Oehlbach Audio Linear 8 - Galvanic isolation filter for turntables & subwoofers - Interference suppression filter to eliminate ground loops.​

Audio Linear 8

Mit dem galvanischen Filter Audio Linear 8 werden potentielle Störfaktoren beim Anschluss sämtlicher Komponenten, wie z.B. einem Plattenspieler oder einem Subwoofer, effektiv eliminiert. Durch jahrelange Erfahrung und technologischen Vorsprung hat Oehlba…

www.oehlbach.com

Will that help? Does it change the sound? I have tried a smaller version that looks like a cable with a mounted transformer and it reduced the hiss already. Any other thoughts?

- Are you using the NAD as a turntable head amp?
- Is the noise there all the time, if you use that input or not?
- have you used a ground wire from the turntable to the NAD?
- If you disconnect the turntable from NAD, but keep the NAD connected to your poweramps, do you still have the noise?

 

[JoachimStrobel]

- Are you using the NAD as a turntable head amp?
- Is the noise there all the time, if you use that input or not?
- have you used a ground wire from the turntable to the NAD?
- If you disconnect the turntable from NAD, but keep the NAD connected to your poweramps, do you still have the noise?

No, I am simply connecting an Amp to the Center pre out. The Turntable works flawless.But yes, I try to disconnect the turntable. It sits 2 m away and is grounded with an extra ground wire to a blind plug.
I was thinking to connect my Amp‘s chassis to the NAD turntable ground.

 

[Plcamp]

Nobody mentioned this so far. Was the problem on a very old Luxman integrated I had.

If they are old and unserviced devices, I would open them up and make sure the single point ground in the power amp still has a solid uncorroded connection to chassis and to green wire ground.

 

[Mr. Widget]

It does sound like a classic ground loop problem.

You chase down a ground loop by working backwards. Connect the amp to the speaker. Do not connect anything to its input. Power up the amp. If there is no hum, power the amp down, plug in the input from the preamp (or what ever its source will be) leaving any upstream gear disconnected. If adding the preamp with nothing else connected to it causes hum, then your ground loop is created in a difference in ground potential between these two devices, if it is still quiet, add components until you hear the hum.

Typically systems run into ground loop problems when you have devices plugged into different household AC circuits, but these can occur when everything appears like it should be fine and every component is plugged into one AC circuit with a proper grounding scheme.

The isolation transformer I mentioned earlier will eliminate a ground loop and will not audibly affect the sound.

 

[LTig]

No, I am simply connecting an Amp to the Center pre out. The Turntable works flawless.But yes, I try to disconnect the turntable. It sits 2 m away and is grounded with an extra ground wire to a blind plug.
I was thinking to connect my Amp‘s chassis to the NAD turntable ground.

Usually a phono preamp has a separate ground connector (a nut with a screw) for the ground of the TT. Use this one instead of the blind plug.

 

[JoachimStrobel]

So,
I tried everything: no phono, plugs close, reversed, disconnect stuff….
I finally admitted defeat and used this Oehlbacher galvanic separator. No more hiss, all perfect. I just do not understand how the thing will not change the sound. I hear nothing, it sounds good.

 

[Rednaxela]

I read I have a hump on my amp.



Sorry. Moving on.

 

[Mr. Widget]

So,
I tried everything: no phono, plugs close, reversed, disconnect stuff….
I finally admitted defeat and used this Oehlbacher galvanic separator. No more hiss, all perfect. I just do not understand how the thing will not change the sound. I hear nothing, it sounds good.

Yes, it sounds like you have a classic ground loop and breaking the connection with the isolator is the best fix.

Is the unit you are using sonically inaudible? Without additional technical information it is impossible to know, but if it sounds good, then use it an enjoy it. If you are concerned that you may be missing something get the Jensen transformers. They are extremely good.

 

[JoachimStrobel]

This Jensen thing cost 200 usd vs 50 for my Ohlbacher. I will try REW sweeps later on my Oehlbacher and report. And save for a new amp.

 

[Mr. Widget]

This Jensen thing cost 200 usd vs 50 for my Ohlbacher. I will try REW sweeps later on my Oehlbacher and report. And save for a new amp.

Well, there is that.
I am not suggesting that there is anything wrong with the Oehlbacher... but I use various transformers from Jensen in my day job. They are the real deal. No BS, pure science and will outlast us all.

 

[antcollinet]

This Jensen thing cost 200 usd vs 50 for my Ohlbacher. I will try REW sweeps later on my Oehlbacher and report. And save for a new amp.

Just by way of a heads up - a new amp can just as easily be subject to ground loops - you'll still be constrained by an unbalanced analogue connection from the NAD. If you're going in that direction, I'd make sure the new amp can input balanced connections, and then put unbalanced to balanced converters directly at the ouputs of the NAD.