AudioNervosa

Electro Stimulation Ward => Signals and Noise => Topic started by: Bigfish8 on November 12, 2009, 04:34:03 AM

Title: 60 cycle Ground Hum
Post by: Bigfish8 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
Title: Re: 60 cycle Ground Hum
Post by: bmr3hc 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
Title: Re: 60 cycle Ground Hum
Post by: rollo 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.


charles
Title: Re: 60 cycle Ground Hum
Post by: mdconnelly 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.
Title: Re: 60 cycle Ground Hum
Post by: tmazz 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

Title: Re: 60 cycle Ground Hum
Post by: BobM 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.
Title: Re: 60 cycle Ground Hum
Post by: tmazz 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.
Title: Re: 60 cycle Ground Hum
Post by: Bigfish8 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
Title: Re: 60 cycle Ground Hum
Post by: richidoo 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:
Title: Re: 60 cycle Ground Hum
Post by: bmr3hc 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
Title: Re: 60 cycle Ground Hum
Post by: Bigfish8 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
Title: Re: 60 cycle Ground Hum
Post by: Bigfish8 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
Title: Re: 60 cycle Ground Hum
Post by: richidoo 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.
Title: Re: 60 cycle Ground Hum
Post by: Bigfish8 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
Title: Re: 60 cycle Ground Hum
Post by: bmr3hc 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
Title: Re: 60 cycle Ground Hum
Post by: tmazz on November 17, 2009, 05:34:43 AM
I don't think you ev er mentioned what kind of amp you are using.  At this point I think you are down to two possibilities. 1) there is a problem with the electrical input to the amp or 2) there is a problem with the amp itself that needs repairing.  :(

I think the best way  to know for sure is to bring the amp over to the home of one of you audio buddies and plug it in there ( this is why I asked what kind of amp it was. If it is a bear to move it might be easier to have somebody else bring an amp to you). Either way, if your amp hums on the same AC line that another one doesn't it would seem like time from a visit with my local technician.

At least this problem sounds like it is constant. I had an intermittent problem in a power amp regulator circuitry once had stopped humming every time I brought it to a shop. Not unlike the kid who makes a miracle recovery suddenly feels well enough to go to school when his mother goes to look for the rectal thermometer. I kind of sorry we use those digital ear thermometers now. When I was growing up I think the rectal thermometer was responsible for getting more sick schoolkids on their feet than all the drugs in the pharmacy combined  :lol:

Hmmm........ I like the old fashiond analg thermometer better than the new solid state digital version. I think I see a pattern here...........

Good luck,
Tom
Title: Re: 60 cycle Ground Hum
Post by: richidoo on November 17, 2009, 07:20:48 AM
Ken uses Odyssey Stratos Mono (maybe the Extreme version?) and Mapletree Line 2A SE preamp with seperate PS module. All JPS SC3 signal wires, Black Sand power wires. Odyssey doesn't give the S/N spec on their website.

There are 2 common types of noise, hum and hiss. 60Hz hum comes from ground loop or EMI from transformer, and 120Hz hum comes from PS after rectifiers. Hiss comes from RFI, and all active circuit components (transistors and tubes) when they are powered on. You need to seal off the input jack on the amp before you listen for output hiss noise. Connect the preamp to the amp, but the preamp is not plugged in, nor is anything connected to it. This will stop any RFI getting into the amp input jack. Then listen for hiss at the speakers. It should be very quiet, if not silent.  It should be fully warmed up also. There may be very soft hiss at the speaker, but you should not be able to hear any noise at all from your listening position, even in dead quiet room. If you can hear it from listening seat, call Klauss to discuss S/N ratio or repair options. Maybe it just needs bias adjusted. If something is broken or out of adjustment, then it should not be happening on both amps. If both amps sound identical, then it is the design. Decide if you can live with it.  I never noticed any noise from them when I have visited your system, even with the horn loaded tweeter - and I am sensitive to it after living with tubes for so long.

But you should not hear any 60Hz hum from the amp with shorted input. If you hear hum with grounded input then it is either poor PS design allowing ripple on the DC rails (120Hz, not 60Hz) or poor internal layout where PS transformer magnetic leakage induces AC current on DC rails or signal wires, or else something is broken or out of adjustment. It's not poor design from Klauss, but he can give you better advice about what to try. It would be a good idea to test the amp noise with a ground buster on the outlet just to make sure it is not related to ground. Test each amp separately, and make sure they are fully warm.
Good luck!
Title: Re: 60 cycle Ground Hum
Post by: Bigfish8 on November 17, 2009, 02:24:07 PM
Guys: 

I called Rich this afternoon and had a conversation about the background noise I am hearing.  He recommended I disconnect everything from the preamp except for one IC to one monobloc amp.  Then to make certain I had the amp and preamp powered from the same double outlet.  When I powered the amp up I had to place my ear to one of the woofers to hear the faintest of hash.  When I powered up the preamp the hiss/hash could be heard.  It is not that it is an extremely loud noise and I do not hear it when playing music; but, I know that background noise is a negative to sound quality. 

The Mapletree has a rectifier in the power supply and I have not evaluated a replacement.  Rolling tubes int he preamp has had no impact on the background noise.  I would also comment that I believe the background noise was present with the Timepiece Speakers but they were 85db efficient into 8 ohms where the Ushers are 90db into 4 ohms.  I believe the higher efficiency of the new speakers make the background noise more apparent.  It will be interesting to hear the impact of a different pre into the system.

Ken
Title: Re: 60 cycle Ground Hum
Post by: satfrat on November 17, 2009, 02:45:55 PM
Ken uses Odyssey Stratos Mono (maybe the Extreme version?) and Mapletree Line 2A SE preamp with seperate PS module. All JPS SC3 signal wires, Black Sand power wires. Odyssey doesn't give the S/N spec on their website.

There are 2 common types of noise, hum and hiss. 60Hz hum comes from ground loop or EMI from transformer, and 120Hz hum comes from PS after rectifiers. Hiss comes from RFI, and all active circuit components (transistors and tubes) when they are powered on. You need to seal off the input jack on the amp before you listen for output hiss noise. Connect the preamp to the amp, but the preamp is not plugged in, nor is anything connected to it. This will stop any RFI getting into the amp input jack. Then listen for hiss at the speakers. It should be very quiet, if not silent.  It should be fully warmed up also. There may be very soft hiss at the speaker, but you should not be able to hear any noise at all from your listening position, even in dead quiet room. If you can hear it from listening seat, call Klauss to discuss S/N ratio or repair options. Maybe it just needs bias adjusted. If something is broken or out of adjustment, then it should not be happening on both amps. If both amps sound identical, then it is the design. Decide if you can live with it.  I never noticed any noise from them when I have visited your system, even with the horn loaded tweeter - and I am sensitive to it after living with tubes for so long.

But you should not hear any 60Hz hum from the amp with shorted input. If you hear hum with grounded input then it is either poor PS design allowing ripple on the DC rails (120Hz, not 60Hz) or poor internal layout where PS transformer magnetic leakage induces AC current on DC rails or signal wires, or else something is broken or out of adjustment. It's not poor design from Klauss, but he can give you better advice about what to try. It would be a good idea to test the amp noise with a ground buster on the outlet just to make sure it is not related to ground. Test each amp separately, and make sure they are fully warm.
Good luck!

Hey Rich, try  Odessey Audio Mexico website for more accurate information on ALL Odyssey products. Eduardo's website should be Klaus's home site. ;)

Cheers,
Robin (http://www.odysseyaudiomx.com/odyssey/amplificadores-stratos.htm)
Title: Re: 60 cycle Ground Hum
Post by: richidoo on November 17, 2009, 04:40:33 PM
Thanks Robin!
Title: Re: 60 cycle Ground Hum
Post by: bmr3hc on November 24, 2009, 04:26:56 AM
Ken

What's the status of the hum? Hopefully resolved? If not what else have you tried to resolve it and what's your next step?

Henry
Title: Re: 60 cycle Ground Hum
Post by: Bigfish8 on November 24, 2009, 04:36:53 AM
Ken

What's the status of the hum? Hopefully resolved? If not what else have you tried to resolve it and what's your next step?

Henry

Hi Henry:

Dr. Sol was over on Saturday to solder some resistors into my Transporter for added protection to the rectifier tube.  When I played the system for him he immediately recognized the noise as a 120hz hum coming from the preamp.  Sol investigated the situation and discovered a grounding loop in the power supply.  A few minutes later, after working his magic, the preamp was dead quite - well expect for a very faint tube hiss.  I was about the kick it out the door and since Sol repaired it I have ordered a NOS Bendix 6X5 Rectifier Tube.  Also Chris of BPT is making a new Umbilical Cord to replace the stock cord between the power supply and preamp.  I am a happy audiophile at the moment. :thumb:

We missed you at the G2G on Saturday!

Happy Thanksgiving!

Ken
Title: Re: 60 cycle Ground Hum
Post by: bmr3hc on November 24, 2009, 05:18:40 AM
Awesome Ken. great to hear that the "hum" problem solved and by none other than Dr. Sol, the problem Sol'ver. Wish I could have been there on Saturday. Still nursing a cold. The good part is I was able to listen to music for hours.

Henry