+ Reply to Thread
Page 1 of 11 123 ... LastLast
Results 1 to 10 of 110

Thread: Ground loop between pre-amp and power amp?

  1. #1
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 534
    I'm Simon.

    Default Ground loop between pre-amp and power amp?

    Ever since introducing separate Pre and Power amps into my set-up I've had humming coming from my speakers, which I am 99.9% sure is a ground loop. I'm currently running an Emotiva UMC-200 and Nakamichi AVP1, before that I was using my old Sony STR-DA2400ES as a pre into the Nak and also had the humming. Before I ever introduced the Nak I was using the Sony AVR solely and had no humming at all.

    When the power amp is connected to the speakers but not the pre, there is no humming so that eliminates the power amp. Soon as the pre is connected up using unbalanced RCA cables the hum appears - before ever connecting any other leads in the pre itself. I can only assume (after thorough research) that because both amps have 3 pin power cables that both are trying to ground and it's throwing something off. Both are plugged into the same power socket via an extension.

    What are my options to remove this ground loop (and safely)?

    I've read that making up a piece of speaker cable to go between them and connecting it to a screw in each chassis is an option but is that even safe, and will it even work?

    I'm struggling to really find any decent info on this as most stuff that comes up regarding ground loops is usually to do with TV/Cable/Satellite and not between 2 amps.

  2. #2
    Join Date: Jul 2011

    Location: Northamptonshire

    Posts: 1,914
    I'm Peter.

    Default

    Hi Simon.

    When I had your power amp, I used it with two different pre-amps and had no problems with hum .. so there is hope! In fact I was taken with how low the hum/noise level was through my sensitive speakers.

    My experience with audio systems is that the culprit is is often a digital source interacting with the pre. Try unplugging any cd / dvd / blueray players at the mains, one at a time. If that doesn't give any joy, then disconnect all source boxes. Many such players seem to have been designed with two pin mains markets in mind.

  3. #3
    Join Date: Mar 2012

    Location: Gloucestershire

    Posts: 3,377
    I'm Paul.

    Default

    Ground loops can be difficult to trace, but you can introduce a ground lift circuit (safely) into the preamp which, more often than not, will cure the problem.

    All you need is a bridge rectifier of sugfficient rating, a capacitor and resistor (in parallel) across the connections from the earth to chassis. A 3.5A bridge rectifier, 100nF cap and 10 Ohm (5 to 10W) resistor is all that is needed.

    Here's one that I made up for my old croft preamp which didn't have one:



    The white cable in from top left is a new earth wire soldered to the star-earth point for the RCA signal ground point which was lifted and insulated from the chassis and redirected to the earth lift circuit. It is intrinsically safe to do this. All wiring is 600V rated and can carry full earth fault from a failure of the circuit too. Output is to existing chassis earth point. AC mains ground is retained. On no account lift the earth from the mains to chassis! (either at the plug or the amp, as was often recommended back in the bad-old days).

  4. #4
    Join Date: Sep 2013

    Location: North Island New Zealand

    Posts: 1,757
    I'm Chris.

    Default

    Quote Originally Posted by Simon_LDT View Post
    Ever since introducing separate Pre and Power amps into my set-up I've had humming coming from my speakers, which I am 99.9% sure is a ground loop. I'm currently running an Emotiva UMC-200 and Nakamichi AVP1, before that I was using my old Sony STR-DA2400ES as a pre into the Nak and also had the humming. Before I ever introduced the Nak I was using the Sony AVR solely and had no humming at all.

    When the power amp is connected to the speakers but not the pre, there is no humming so that eliminates the power amp. Soon as the pre is connected up using unbalanced RCA cables the hum appears - before ever connecting any other leads in the pre itself. I can only assume (after thorough research) that because both amps have 3 pin power cables that both are trying to ground and it's throwing something off. Both are plugged into the same power socket via an extension.

    What are my options to remove this ground loop (and safely)?

    I've read that making up a piece of speaker cable to go between them and connecting it to a screw in each chassis is an option but is that even safe, and will it even work?

    I'm struggling to really find any decent info on this as most stuff that comes up regarding ground loops is usually to do with TV/Cable/Satellite and not between 2 amps.
    Check your RCA connectors, that ground one end is 0.00 ohms, ground the other end. You may have a broken lead. Don't get distracted by 3 pin cables and safety earth
    all are there for good reason. Ah ! , UNPLUG FIRST and check your extension lead that it has been wired correctly. If wired incorrectly or earth not connected there is likely your fault.
    Always use a properly manufactured extension lead. The typical result with a lead wired wrongly, is 1/2 your AC mains voltage then on all chassis metal. Hence WHY and for other
    serious faults AC mains GND must always be connected.

    Cheers / Chris

  5. #5
    Join Date: Apr 2013

    Location: Granes - Haut Vallee de l'aude - EU

    Posts: 2,831
    I'm Richard.

    Default

    Yup - for definite always keep the safety ground. Do not disconnect earth.

    If it hums with no inputs connected on the preamp then it is not noise coming in from a digital source interacting with the preamp
    Strictly you should blank off the inputs on the pre with null plugs - but I doubt that is the issue
    Obviously the preamp may have an internal hum fault. If you can get a simple 2rca to 3.5mm jack, you can listen to the preamp out on headphones and eliminate that possibility
    My next favourite to confirm a ground loop is signal lead transformers - but I don't suppose you have one in your locker
    A good first try is to make a connection from chassis ground on the pre to chassis ground on the power amp - although if both are grounded to earth using the same electrical socket that would be unusual.
    As others have noted, check connecting leads and the multiway are wired properly. It is not uncommon for neutral and earth to get swapped.

    Report back -but don't lift safety grounds.

  6. #6
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 534
    I'm Simon.

    Default

    Thanks for the replies so far. Will be unplugging everything and doing another check shortly.

  7. #7
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 534
    I'm Simon.

    Default

    Right, this is really strange. Unplugged everything and plugged back in the power amp and processor/pre (I've already confirmed that the power amp itself is not causing an issue as with all 3 channels I currently have connected to it are hum-free at this stage).

    I then plugged in the surround right rca lead and no hum occurs. I then plug in the surround left rca lead and then the hum starts (and is in both rear channels). Why would plugging in a 2nd rca lead cause this? I even tried a different rca lead and the same thing happens. Even tried a different input (in case it was faulty) and again the same result. I haven't even plugged in anything else (HDMI, Optical, Coaxial, etc) yet the same hum is already there...

  8. #8
    Join Date: Mar 2015

    Location: Auckland, New Zealand

    Posts: 289
    I'm Deano.

    Default

    Quote Originally Posted by Light Dependant Resistor View Post
    Check your RCA connectors, that ground one end is 0.00 ohms, ground the other end. You may have a broken lead. Don't get distracted by 3 pin cables and safety earth
    all are there for good reason. Ah ! , UNPLUG FIRST and check your extension lead that it has been wired correctly. If wired incorrectly or earth not connected there is likely your fault.
    Always use a properly manufactured extension lead. The typical result with a lead wired wrongly, is 1/2 your AC mains voltage then on all chassis metal. Hence WHY and for other
    serious faults AC mains GND must always be connected.

    Cheers / Chris
    Definitely check the wiring on the plug end, I bought a iec power cord from a reputable company in Australia and had a serious hum coming though the speakers and couldn't identify the issue, hum was coming through when phonostage was selected on input on pre amp and also cd player, finally found the problem but not after my krell blew a transistor, the issue was the ground pin was live, a major and potential catastrophic accident waiting to happen and basically i used the power cable to run from the wall socket to the power conditioner block, so basically anything that was plugged into the conditioner strip was then live on the ground, the cable made one live ground into 5 live grounds (5 sockets) unbelievable, so please everyone check the pins are correct on the cables before plugging into your prized possessions

  9. #9
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 99,005
    I'm Grant.

    Default

    Check to see if it is earthing properly with a meter( the socket on amp)
    Regards,
    Grant .... ؠ ......Don't be such a big girl's blouse

    I've said it before and I'll say it again: democracy simply-doesn't-work
    .... ..... ...... ...... ................... ..... ..... ..... ..... .....
    FIIO K7 BT, M11 PLUS, BTR7, KA5 - OPPO BDP-103D - PANASONIC UB450 - PANASONIC 4K ULTRA HD TV - PIXEL 6 - AVANTREE LR BLUETOOTH - 2* X600 SOUNDCORE - HEADPHONES INCLUDE, FIIO, NURAPHONES', FOCAL, OPPO, BOSE, CAMBRIDGE, BOWER & WILKINS, DEVIALET, MARSHALL, SONY, MITCHELL & JOHNSTON - 2*ZBOOK'S- MERCURY BD ROM, ROON, QOBUZ, TIDAL, PLEX, CYBERLINK, JRIVER - MULTI HDD'S -

    Oh my god! There's nothing wrong with the bidet is there?

    “Nothing discloses real character like the use of power. It is easy for the weak to be gentle. Most people can bear adversity. But if you wish to know what a man really is, give him power. This is the supreme test. It is the glory of Lincoln that, having almost absolute power, he never abused it, except on the side of mercy".

    “You see these dictators on their pedestals, surrounded by the bayonets of their soldiers and the truncheons of their police ... yet in their hearts there is unspoken fear. They are afraid of words and thoughts: words spoken abroad, thoughts stirring at home -- all the more powerful because forbidden -- terrify them. A little mouse of thought appears in the room, and even the mightiest potentates are thrown into panic.”

    "You don't have free will. You have the appearance of free will.”

    “There's a war out there, old friend. A world war. And it's not about who's got the most bullets. It's about who controls the information. What we see and hear, how we work, what we think... it's all about the information!”


    ***SMILE, BE HAPPY***

  10. #10
    Join Date: Jul 2011

    Location: Northamptonshire

    Posts: 1,914
    I'm Peter.

    Default

    Almost certainly not the problem, but just check all the 7 channels on the nak are switched to rca (not xlr). Can't imagine it would make a difference, but ...

    Also, does your processor have any ground switches on the back? Some stuff I've had in the past has a ground lift switch, or one you flip for rca or xlr outputs.

+ Reply to Thread
Page 1 of 11 123 ... LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •