[freo]

Hello
I have a hum going through my system, it is even worse with my new, very efficient speakers, when I place a hum eliminator in between the power amp and pre amp the hum goes away, the only problem is I seem to loose some sound quality. My questions are, why would the hum go away with the hum eliminator and is there anything else I could do to achieve the same results, also has anyone used a particular brand of these gadgets that worked without lose of dynamics
Regards from Australia Roger

[Gordy]

I built the 2 Diode drop DC Blocker   as described here... http://www.audiocircle.com/index.php?topic=50908.10  Works a treat with no current restriction problems in my system for transformer buzz.

[andyr]

Hello
I have a hum going through my system, it is even worse with my new, very efficient speakers, when I place a hum eliminator in between the power amp and pre amp the hum goes away, the only problem is I seem to loose some sound quality. My questions are, why would the hum go away with the hum eliminator and is there anything else I could do to achieve the same results, also has anyone used a particular brand of these gadgets that worked without lose of dynamics
Regards from Australia Roger

Hi Roger,

1.  IME (as a DIYer!!   ), hums only appear if your system contains a fundamental flaw (so they should be able to be removed by fixing this "flaw"), and
2.  While most of the time, hum is caused by an earth-loop "problem", sometimes hum can be caused by other ... unexpected things!    I recently solved a hum that had been bugging me for a year when I connected a sub into my system ... I eventually solved it (ie. made the hum go away) by changing the earthing scheme on my preamp (which was wrong to start with, except that the "wrongness" hadn't shown up until I added the sub).

I don't know what your "hum eliminator" actually is but if it's something that the signal has to pass through (between pre and power amps) then it stands to reason it will be degrading the signal.  

So that we can help you better, can you do some initial diagnosis of your situation, along the following lines:

a) is this hum volume dependent (ie. does it get louder when you turn up the volume control on your preamp)?
b) if you disconnect the IC between your pre and power amp, does the hum go away?
c) if you have the pre connected to the power amp, does the hum go away if you take out the IC between source and pre?
d) what are the mains connections on your pre and power amps.  By this I mean:
    - do they have 2-wire mains or a proper 3-wire (grounded) mains cord?
    - if so, is there a connection between the earth pin (the central pin) of the IEC socket and the chassis?  Or in the case of a captive mains cord, is the earth wire attached to the chassis?
    - if the component has a conventional PSU (with power transformer), is the centre tap of the mains transformer connected to the chassis?
e) is any part of a component connected to the chassis ... eg. input RCA sockets? ... speaker return BPs? ... PSU earth?
f) do you have your system components plugged into just 1 mains circuit or several?

Regards,

Andy

[freo]

a) is this hum volume dependent (ie. does it get louder when you turn up the volume control on your preamp)?  NO, CONSTANT HUM
b) if you disconnect the IC between your pre and power amp, does the hum go away?   VERY SLIGHT WITH EAR AGAINST SPEAKER
c) if you have the pre connected to the power amp, does the hum go away if you take out the IC between source and pre? NO STILL THE SAME
d) what are the mains connections on your pre and power amps.  By this I mean:
    - do they have 2-wire mains or a proper 3-wire (grounded) mains cord? 3 WIRE
    - if so, is there a connection between the earth pin (the central pin) of the IEC socket and the chassis?  Or in the case of a captive mains cord, is the earth wire attached to the chassis? YES
    - if the component has a conventional PSU (with power transformer), is the centre tap of the mains transformer connected to the chassis? YES
e) is any part of a component connected to the chassis ... eg. input RCA sockets? ... speaker return BPs? ... PSU earth? NOT SURE
f) do you have your system components plugged into just 1 mains circuit or several? JUST ONE
Thanks for the reply Andy, hope this helps, I have valve pre (bottlehead) diy class a amp with sep power supply (altronics) pi 2 tower speakers Zhaulu dac

[andyr]

a) is this hum volume dependent (ie. does it get louder when you turn up the volume control on your preamp)?  NO, CONSTANT HUM
b) if you disconnect the IC between your pre and power amp, does the hum go away?   VERY SLIGHT WITH EAR AGAINST SPEAKER
c) if you have the pre connected to the power amp, does the hum go away if you take out the IC between source and pre? NO STILL THE SAME
d) what are the mains connections on your pre and power amps.  By this I mean:
    - do they have 2-wire mains or a proper 3-wire (grounded) mains cord? 3 WIRE
    - if so, is there a connection between the earth pin (the central pin) of the IEC socket and the chassis?  Or in the case of a captive mains cord, is the earth wire attached to the chassis? YES
    - if the component has a conventional PSU (with power transformer), is the centre tap of the mains transformer connected to the chassis? YES
e) is any part of a component connected to the chassis ... eg. input RCA sockets? ... speaker return BPs? ... PSU earth? NOT SURE
f) do you have your system components plugged into just 1 mains circuit or several? JUST ONE
Thanks for the reply Andy, hope this helps, I have valve pre (bottlehead) diy class a amp with sep power supply (altronics) pi 2 tower speakers Zhaulu dac

OK, from your answers, we can eliminate some obvious possibilities but now you'll need to examine the bottlehead circuit/build and the Altronics amp to find out whether:
* RCAs are attached to the case in any way
* is there a small resistor - typically 10 ohms - separating "signal ground" from "power ground" on either the power amp or the Bottlehead?

Now, your answer to b) above is a bit confusing.  I assume you have basically an "unlistenable" level of hum normally ... but when you disconnect the IC between your pre and power amp, the hum basically goes away so that you can just hear it with your ear against the speaker?

If so, that low level of hum you may have to put up with ... and as you shouldn't be able to hear it from your listening position, there shouldn't be a problem?

If removing the IC from the Bottlehead to the power amp stops the hum, that says to me there is something incompatible between the topology used for the Bottlehead and the topology used for the Altronics.  Is the case of the Altronics amp earthed back to the case of the separate PS (which you said was earthed to mains earth)?

IME, if you adopt a construction methodology which involves the following:
* the only thing connected to a case is the earth wire from the mains cord (for safety reasons) - or the earth pin on the IEC socket.
* the centre tap from the power transformer is therefore not connected to chassis "earth" ... it is connected to the "ground" on the power supply, where the speaker returns and the ground wire to the amp/preamp circuit also connect.
* signal ground is "lifted" from power ground all the way through the system.

... then you shouldn't get any hum.

Regards,

Andy

[NewBuyer]

Hello
I have a hum going through my system, it is even worse with my new, very efficient speakers, when I place a hum eliminator in between the power amp and pre amp the hum goes away, the only problem is I seem to loose some sound quality. My questions are, why would the hum go away with the hum eliminator and is there anything else I could do to achieve the same results, also has anyone used a particular brand of these gadgets that worked without lose of dynamics
Regards from Australia Roger

In your described case, your ground loop issue is probably best solved with the Hum Eliminator you are currently using. Is your eliminator made by EBTech/Morley? Those contain output transformers which are very good quality, but you might get even better performance by using an input transformer (from Jensen) or even the EbTech HumX product, which looks interesting.

Another option you could try if interested, is to use a passive preamp solution - which is great if you have only one source, etc

Good luck fixing this problem - I hate ground loops, they are a primary reason why I eventually ditched the RCA connections entirely and went with all balanced/XLR connections (which I've found to sound much better too).

[freo]

Thank you all for your replies, I will try to fix the problem by tying the audio signal of my bottlehead pre to its chassis/safety ground to see if that works, I will let you know how I get on
Regards Roger

[andyr]

Thank you all for your replies, I will try to fix the problem by tying the audio signal of my bottlehead pre to its chassis/safety ground to see if that works, I will let you know how I get on
Regards Roger

Roger,

By all means try it - because solving hum problems can require unorthodox means and be very tricky to accomplish - but IME you do not want any part of the circuit to be attached to the chassis (which you said was attached to mains earth).

Regards,

Andy

[freo]

Hi Andy
Thanks for your help in my quest in eliminating hum from my system, I went ahead with my little plan and of course it did not work, the hum was twice as loud as normal, I will have to get my head around your recommendations, I am one of those people who build things like pre and power amps and speakers but can't read a schematic.  One thing I did notice after I had undone my grounding I replaced the ic with another one I had lying around and the hum was cut in half, the ic I had in was very long about 2m, this one is about .5m. Point D in your questions my answers should have been 3pin-no-no  and E no. Anyway thanks again for your help
Regards Roger

[jaywills]

You might try a Jensen Transformers ISO-MAX PC-2XR Balanced to Unbalanced Audio Converter (no affiliation).  My Melos tubed pre-amp injected a hum into my system and placing the Jensen transformer between it and my power amp solved the problem.  Haven't noticed any loss of resolution, dulling, etc. of the signal.  Good luck.  Cordially,

[JoshK]

Jensen Transformers are very good.  Plus your tube preamp probably prefers to see the inductive load of the tranformer to the capactive load of your amp.