Author Topic: 60 cycle Ground Hum  (Read 8341 times)

Bigfish8

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60 cycle Ground Hum
« on: November 12, 2009, 04:34:03 AM »
Guys:

I am picking up a very low 60hz ground hum when I turn on my preamp.  I have plugged all of my audio gear into one of my dedicated 20 amp lines (a total of 6 outlets on the one line fed by 10 guage Romex).  The problem was there present prior to running the dedicated line(s) and therefore the problem is not with the line.  It is interesting I have no noise coming from the speakers with only the amps turned on which stay on all the time.  It is only after I turn-on the preamp that I hear the hum. 

I would greatly appreciate any helpful suggestions.

Thanks,

Ken

Offline bmr3hc

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Re: 60 cycle Ground Hum
« Reply #1 on: November 12, 2009, 05:25:57 AM »
Sounds like the dreaded Electromagnetic Interference monster (EMI)

The usual suspects for EMI are:

1.Preamp too close to amp.

2. Preamp power cords too close to input/output IC cables

3.IC cables too long. should be kept as short as possible ( 3 meters or less.)

4. Non shielded cables. Shielded cables should help.

Try repositioning your pre amp IC and power cord. see if that helps. If not, try repositioning your pre amp farther away from your amp. If all else fails, try checking the preamp IC being completed inserted ( I know, it has happened to me a time or two) from preamp to amp.

I am sure there are other factors not mentioned here. These are ones I have dealt with. What Kind of preamp do you have? Tube or SS?

Henry
"If music be the food of love, play on."  Shakespeare

Offline rollo

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Re: 60 cycle Ground Hum
« Reply #2 on: November 12, 2009, 09:00:31 AM »
 You may want to try a cheater plug at the Preamp. Reverse the polarity and listen. Now the other components one at a time.   Check all your ICs. Using tubes ? Does the hum come from both channels or just one ? My hum was from an IC that was shieleded with the shield connected to ground. Go figure. 
   Besides the obvious how is your wire management ? Anything touching one another. ICs close to powercords ?
   Changing ICs did it for me. Interferring ground potentials I quess, who knows. Anyway when I installed the Alan Maher CBF Mum is the word . Dead quiet.


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Offline mdconnelly

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Re: 60 cycle Ground Hum
« Reply #3 on: November 12, 2009, 10:02:05 AM »
Ken,

Did you get a chance to try the AM Infinity CBFs that Shane picked up?  Just curious if you did and if that has any affect on the hum you're hearing.  Not sure if it would make a lick of difference, but if it is EM or RF related, it might.

Offline tmazz

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Re: 60 cycle Ground Hum
« Reply #4 on: November 12, 2009, 11:30:13 AM »
Three other things to try:

1) If you have access to a digital voltmeter, use the lowest scale and check for a voltage difference between the chassis of the amp & preamp. Both chassis should be at (the same) ground potential so you should see zero volts between them. If you get a reading there is something amiss. When for both AC and DC voltage. Remember, you will have to find a patch of bare metal to do this. Taking readings through paint  or any other kind of coating could skew the results.

2) Check the electrical integrity of your AC outlet. You can get a small device at Radio Shack that plugs into your AC outlet and tells you if the hot and Neutral lines are assigned to the correct sides of the plug and if the third prong has a good solid ground back to the breaker box.

3) Do you have a turntable connected to the preamp? If so try disconnecting it (both the L&R signal cables and the ground wire. The phono section of a preamp is by far the highest gain stage and therefore can easily pick up stray signals that would get lost under the noise floor of a lower gain section. If this doesn't work Disconnect all of your input cables one at a time and see if removing any particular source solves the problem. If it does solve the problem, then switch out the IC cable for that component to see if the hum is caused by the cable or the source component itself.

Good Luck,

Tom

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Offline BobM

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Re: 60 cycle Ground Hum
« Reply #5 on: November 12, 2009, 12:00:25 PM »
I agree with Tom. You need to "trace back" and identify the component that it the culprit. Start at the source end and unplug things one at a time. First unplug the interconnect and see if it goes away, if not then reconnect the interconnect and turn off the component, if not then unplug the AC on that component.

If not then move on to the next component in the line until you finally touch or do something that stops the hum. But be sure to mute when unplugging anything.

Is your preamp tubed? You could be getting a transformer hum also, and not just a ground loop (but that is more likely the situation). Check and see if it goes away with something heavy on the transformer, like a lead weight.
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Offline tmazz

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Re: 60 cycle Ground Hum
« Reply #6 on: November 12, 2009, 12:35:36 PM »
And while we are all looking for a component interaction, it could also be a power supply problem within the preamp itself, but you won't know that until you eliminate all the other possibilities.
Remember, it's all about the music........

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Bigfish8

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Re: 60 cycle Ground Hum
« Reply #7 on: November 12, 2009, 12:59:14 PM »
Guys:

Thank you very much for the information you have provided.  When I get back home I will start trying to eliminate things per your recommendations.

Ken

Offline richidoo

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Re: 60 cycle Ground Hum
« Reply #8 on: November 12, 2009, 02:27:11 PM »
The mapletree preamp has separate PS, so EMI is less likely, transformer is at least 12" from the tubes. Ken uses very well shielded ICs.

Ken, is this the same hum you asked about on AC having to do with the DirecTV or is that a different system? The reason I ask is because even if the DirecTV is shut off, the mere connection of the grounded antenna wire to any part of the system will still give you the hum even if the directv is shut off. It gets in on the ground of single ended interconnects, or on the shield of correctly grounded antennas.

Verify it is not the preamp causing the hum by running it into one poweramp, both plugged into the same outlet, with no sources connected to the preamp input. Disconnect everrything except the single connection to the poweramp. If no hum, then add in the other poweramp, using the normal outlets for each component. If it hums, then try the ground buster on the preamp. If it is quiet, then the preamp is clean, you can start adding sources. If not quiet, lift the ground on one amp and plug the preamp into the same outlet as the grounded amp. If still hums, get a new preamp.. but I don't think it will unless it is EMI.

Add only one source at a time. Disconnect  a clean source before testing a different one. If none of them hum, that means the hum is between two of the sources. Start adding them in together one at a time. When you find the hum, start removing the other sources until you narrow down which two make the hum.

In the end you can either lift signal grounds in the preamp or source (surgery,) lift safety ground with ground buster (not recommended,) use floating ground with balanced power transformer, isolate coax antenna with cap or transformer, or isolate analog signal with cap or transformer, or get an iPod.  :rofl:

Offline bmr3hc

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Re: 60 cycle Ground Hum
« Reply #9 on: November 15, 2009, 04:29:38 AM »
Ken

Curious to know if the hum problem has been resolve? If so, what was the cause?

Henry
"If music be the food of love, play on."  Shakespeare

Bigfish8

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Re: 60 cycle Ground Hum
« Reply #10 on: November 16, 2009, 04:17:45 AM »
Ken

Curious to know if the hum problem has been resolve? If so, what was the cause?

Henry

I had to go to the Eastern Shore this weekend to access the wind/rain damage (they had 75 mph winds and more than 14 inches of rain from this storm) and did not have the opportunity to check the system this weekend.  I will keep you guys posted.

Ken

Bigfish8

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Re: 60 cycle Ground Hum
« Reply #11 on: November 16, 2009, 05:29:09 PM »
Guys:

I unplugged the signal from the preamp to the amps and listened to the speakers.  I could hear some very low noise.  The only action I could take was to connect the amps to some different outlets and the result was no change in the very low noise.  I guess I am getting hash off the grid and will need to try some type of power conditioner to determine if I can get rid of the noise.

Ken

Offline richidoo

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Re: 60 cycle Ground Hum
« Reply #12 on: November 16, 2009, 08:06:23 PM »
Any tube preamp will always make some low level noise, compared to a dead silent SS preamp. Some quiet hiss is normal, and also a small amount of inductive hum in the price range of the Mapletree. But if you want to reduce it further, you have to take small systematic steps.

Bigfish8

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Re: 60 cycle Ground Hum
« Reply #13 on: November 17, 2009, 04:04:15 AM »
Any tube preamp will always make some low level noise, compared to a dead silent SS preamp. Some quiet hiss is normal, and also a small amount of inductive hum in the price range of the Mapletree. But if you want to reduce it further, you have to take small systematic steps.

Rich:

I am hearing the hash with no preamp connected to the amps.  With just the amps plugged into the outlet and connected to the speaker I hear a low hash.  The sound then gets louder when I plug in the preamp.  Although I tried plugging the amps into different outlets I was unable to obtain dead silence with the preamp out of the circuit. 

Ken

Offline bmr3hc

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Re: 60 cycle Ground Hum
« Reply #14 on: November 17, 2009, 05:14:17 AM »
If speaker wires are on carpeted floors, try lifting them up off the carpet where static build up. Also, be sure your amp power cord is away from speaker wires. If they must cross then have them cross at 90 degrees if I remember correctly. Is the amp tube or SS? If tube then that may be inherent to the tubes. Also, what kind of lighting is near by. I remember some florescent lighting interferes with some electronics especially tubes.

Henry
"If music be the food of love, play on."  Shakespeare