[schw06]

Here's the scenario. Please help with the diagnosis/fix:
-I have a dedicated room with dedicated circuits. Despite this, it almost doesn't seem to matter what preamp and amp I hook up there is a loud mechanical hum that comes out of the speakers. I take the same preamp and amp to a friend's house and they are perfectly quiet. If I use a source directly to an integrated amp it is always quiet. Does this make sense? Is there a logical conclusion/fix? Thanks!
David
P.S.- I've tried various iterations of grounded and ungrounded sources and preamps...Almost doesn't seem to matter.

[dBe]

What do you guys think?  DC or......... split ground....?........

When was it converted to a listening room and by whom?

[TomS]

Dave, I've been there and would guess split ground or something along those lines. Not to say there isn't also some DC though.

Does it hum if you take a preamp and power amp upstairs and connect to some other simple (lightweight) speakers there?

[avahifi]

To track down hum and noise issues, simplfy your setup first!!

In this case, connect only the power amp to the speaker wires and the speakers, with nothing connected to the power amp input jacks!

Turn the amp on.  Does the hum appear?  If so, you have a power amp fault or something seriously wrong with your AC power.  If the hum is originating within your power amp, not from the speakers themselves, you may have low level DC riding on your AC power line.  Our HumDinger ($125) will eliminate this issue.

Or -- - are you using some kind of exotic non-standard speaker wires?  They could be picking up broadcast noise from something else close by.  Standard two conductor zip cord, twisted 3-4 times per foot in an electric drill, will shield speaker wires from most external noise sources.

If the setup is quiet with only the power amp connected then turn it off and add the preamp, but with the only interconnect cables used from the outputs of the preamp to the inputs of the power amp, no source connections yet.  Turn the setup back on.  Does the hum now reappear?  If not the issue is with a source or its connection, if the hum does now show up, the issue is with the preamp or the interconnect cables (perhaps poorly shielded or with a broken or open ground connection).

Follow the above steps exactly and let me know when and if the hum reappears.

651-330-9871

Frank Van Alstine

[schw06]

I want to personally thank Frank Van Alstine for speaking with me over the phone and we did some troubleshooting. Riddle me this. The power amp has no hum without interconnects but hums when you add the preamp (this combination was dead silent at my friends house earlier today). I made sure to use mundane well shielded cables and tried 2 different preamps...hum with the preamp on. I tried a different circuit on a different panel...hum. I then shut off every circuit in the house except the dedicated circuit to the system...hum. Does this mean I have a problem with the AC as it enters the house?

[Roger A. Modjeski]

I want to personally thank Frank Van Alstine for speaking with me over the phone and we did some troubleshooting. Riddle me this. The power amp has no hum without interconnects but hums when you add the preamp (this combination was dead silent at my friends house earlier today). I made sure to use mundane well shielded cables and tried 2 different preamps...hum with the preamp on. I tried a different circuit on a different panel...hum. I then shut off every circuit in the house except the dedicated circuit to the system...hum. Does this mean I have a problem with the AC as it enters the house?

Although this may or may not  help in this situation one should always short the input of the power amp with a shorting plug or better yet a resistor that is equal to the output impedance of the preamp. In almost all cases a shorting plug will do the job. An open input is not a good test for several reasons. Some amplifiers actually have less gain when the input is open, the point being that an amplifier is not meant see an open circuit at its input.

Do as Frank said and start with the power amp connected to the speakers and put a shorting plug in the input. The add in the preamp. If that is quiet add in a source. In general only the power amp should be grounded.

[Big Red Machine]

Have you taken a meter to your cables to make sure there is not a short in there somewhere?

Have you popped the top to make sure a lead inside either unit isn't loose and shorting?

[schw06]

Thanks for the reply. I have tried 2 different pairs of interconnects including Blue Jeans and the same amp/pre were used at a friend's house earlier today with no issues. I also tried a different preamp...hummmmmm. Am I just in a vortex of hell?

[Roger A. Modjeski]

Thanks for the reply. I have tried 2 different pairs of interconnects including Blue Jeans and the same amp/pre were used at a friend's house earlier today with no issues. I also tried a different preamp...hummmmmm. Am I just in a vortex of hell?

Have you tried the shorting plugs on the input of the amp? If you don't have any take an old cheap interconnect, cut the wire so there is about 2 inches left, strip the hot and ground, twist them together and  now you have a shorting plug.

I stress this because some amps have internal ground loops which are only activated by shorting the input (which is in essence what a preamp does). An interconnect open at the other end is a false test.

[schw06]

I don't own any shorting plugs. I have also noticed this same phenomenon with numerous amp/preamp combinations and I have tried every single iteration of grounding without any resolution. Thanks for weighing in on this!

[Roger A. Modjeski]

I don't own any shorting plugs.

See above where I tell you how to make some in a jiffy.

[schw06]

I will work on that. Thank you!

[Roger A. Modjeski]

For everyone looking at this post: Hum problems can be difficult to solve. From my experience they are rarely caused by "dirty AC" I have almost never solved one with a power conditioner.

I have solved them with shorting plugs and ground lifts. You must use shorting plugs on the input of a power amp to assess its resident hum.  Every preamp has an output impedance that the power amp sees. When the amp looks at an open input or cable open at the other end it sees an open circuit which is not what is sees when the preamp is connected.

When the preamp is put back into the system, with no sources connected, hum is usually caused by a loop between the preamp ground and power amp ground. This is where the ground float comes in. Keep the power amp grounded as it has the largest leakage current to ground due to its large transformer. The interconnects between the power amp and preamp will then ground the preamp without the loop. The system will be safe because the preamp is grounded via the interconnect to power amp, you simply don't need the other ground via the power cord. If your preamp has a large leakage current you should try reversing the power cord polarity, which you can now do with the float attached. In my system I have a number of IEC cords where I have simply removed the ground pin. Its cleaner than a float and reversible in the socket. We all have plenty of old computer cords sitting around to scavenge.

If you system hums with the preamp/poweramp combination you also have to consider the preamp may have resident hum, even with the volume down. Remember most preamps have the line stage after the volume control so that is still sending out signal. No volume does not mean no output.

I have found that the resistance of the shield in an interconnect can make a big difference in low level hum.  Use a heavily braided shielded cable when in doubt. You can also try adding a heavy wire between the preamp and power amp chassis to re-reinforce the shield resistance. This extra wire should be spiraled around the interconnect so as not to make a loop.

A ground loop is simply a circle of grounded wires that is large enough to let magnetic flux enter. It forms what you might imagine as a shorted turn in a transformer. In a shorted turn the current is very high and thus a voltage is created between the pre and power amp. You can often move cables around an hear the hum change in volume and character. This is because you are modifying the shape and size of the loop. One of the virtues of balanced lines is that they avoid this problem as the chassis ground is not part of the signal path.

Be especially mindful of amplifiers where the input jacks are separated by a large distance on the back panel. If the power transformer sits between these jacks dress the cables in such a way to make them symmetrical around the transformer. This is something you have to experiment with. In extreme cases breaking the shield on one cable will reduce hum. You need only one interconnect to carry the signal ground between chassis.

Once you get the preamp and power amp combination quiet you can add in sources one at a time.

[Roger A. Modjeski]

oops, I quoted my self by mistake. 

[kentj1948]

Are you plugging your amp and preamp (and source) into two different outlets?  If so plug everything into the same outlet (use an extension strip if necessary) and see if the hum disappears.  Despite being dedicated, you could have outlets at different ground potentials.  If that doesn't help, stop at a hardware store and get a $5 polarity tester.  Use it to check the grounding and wiring of all your dedicated circuits.  Perhaps a hot and neutral are reversed.  If they aren't correctly wired, that might be the source of your problem.

This ebay listing shows the type of tester I am talking about.  I hope this is helpful.   

http://www.ebay.com/itm/Eagle-GFCI-Ground-Fault-Outlet-Tester-Receptacle-Circuit-Tester-Ground-Fault-/271443637151?pt=US_Tools_Crimpers_Strippers&hash=item3f334d339f

[Speedskater]

oops, I quoted my self by mistake. 

There is no better person on this entire forum to quote!

The amount of good information that you have added to many threads is truly impressive.

[Speedskater]

While RAM did an excellent job describing ways to fix this problem, but if you want step by step instructions complete with 8 by10 glossy photos, see this Bill Whitlock seminar paper. Start at page 99 the trouble shooting section.

"An Overview of Audio System Grounding and Interfacing"
by Bill Whitlock, President
Jensen Transformers, Inc.
Life Fellow, Audio Engineering Society
Life Senior Member, Institute of Electrical & Electronic Engineers

http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

[jea48]

Here's the scenario. Please help with the diagnosis/fix:
-I have a dedicated room with dedicated circuits. Despite this, it almost doesn't seem to matter what preamp and amp I hook up there is a loud mechanical hum that comes out of the speakers. I take the same preamp and amp to a friend's house and they are perfectly quiet. If I use a source directly to an integrated amp it is always quiet. Does this make sense? Is there a logical conclusion/fix? Thanks!
David
P.S.- I've tried various iterations of grounded and ungrounded sources and preamps...Almost doesn't seem to matter.

I want to personally thank Frank Van Alstine for speaking with me over the phone and we did some troubleshooting. Riddle me this. The power amp has no hum without interconnects but hums when you add the preamp (this combination was dead silent at my friends house earlier today). I made sure to use mundane well shielded cables and tried 2 different preamps...hum with the preamp on. I tried a different circuit on a different panel...hum. I then shut off every circuit in the house except the dedicated circuit to the system...hum. Does this mean I have a problem with the AC as it enters the house?

Thanks for the reply. I have tried 2 different pairs of interconnects including Blue Jeans and the same amp/pre were used at a friend's house earlier today with no issues. I also tried a different preamp...hummmmmm. Am I just in a vortex of hell?

Thanks for the reply. I have tried 2 different pairs of interconnects including Blue Jeans and the same amp/pre were used at a friend's house earlier today with no issues. I also tried a different preamp...hummmmmm. Am I just in a vortex of hell?

I have a dedicated room with dedicated circuits. Despite this, it almost doesn't seem to matter what preamp and amp I hook up there is a loud mechanical hum that comes out of the speakers. I take the same preamp and amp to a friend's house and they are perfectly quiet. If I use a source directly to an integrated amp it is always quiet.


"there is a loud mechanical hum that comes out of the speakers."


Do you mean a loud AC 60 Hz, cycle, hum coming from the speakers?

If that is what you mean sounds like a ground loop hum to me.

Are the power cords for the preamp and power amp grounding type?

You say you have dedicated circuits in your audio room. Is the preamp and power amp plugged into two different dedicated circuits? If so for a test plug both the preamp and power amp into the same wall duplex receptacle.  Note, only the preamp and power amp. No source ICs connected to the preamp inputs. Check for hum…..

If you still hear the 60 Hz hum, do you have an AC volt meter? If so I would like you to take some readings at the wall duplex receptacle you tested the preamp and power amp in.
First test.
Unplug the preamp and power amp from the wall duplex receptacle, (recept).
Insert each test probe of the volt meter into the mains hot and neutral contacts slots of one the recepts. You should measure around 120Vac.

Next, insert one test probe of the meter in the hot slot, (smaller of the two slots) of one of the recepts of the duplex and the other test probe of the meter in the equipment ground hole of the recept. Make sure you make good contact with the ground contact.
You should measure the same voltage as you measured from the mains hot and neutral above. Somewhere around 120Vac.

Next insert one test probe of the meter into the neutral slot, (larger of the two slots, or in the case of a 20 amp recept the "T" slot), and the other test probe in the equipment ground hole contact. Again make sure the probes make good contact. You should measure zero volts.

Next,  plug in the power amp only into one of the recepts of the duplex recept. Turn on the power amp. Repeat all the above tests using the other recept of the duplex. This will give an actual branch circuit load test.  Post back your results.
Jim 

[schw06]

Thanks for all the input. Just some background info on the basics.
-Everything is plugged into the same outlet
-The exact combinations of preamps and amp are silent at a friend's house
-all outlets are properly wired
-yes it is a 60hz hum
-I have tried a preamp with no ground and a captive cord as well as another preamp with a grounded cord...makes no difference in the hum
   I actually had an electrician that has done work for local recording studios come out yesterday and even he is befuddled. The only things he came up with were that the ground rod is corroded outside the house and he thinks the contact from the grounding wire is poor. He will replace that. Also, one of the electrical panels is inside the room and he thinks there many be some noise being induced by the proximity of the panel. He's the 3rd electrician and it doesn't seem to matter which amp and preamp I put in the system. Even matching preamp and amp from the same manufacturer causes the issue (with shielded IC's and various power cords)

[sfox7076]

Can you hook up the amp with interconnects plugged in but no load connected?  Not the best advice, but I wonder if there would be a hum then.  Seems to me that there could be an issue with the inputs on the amp and RFI or the like.  Now why it is different at your place vs. your friend may be the amount of RFI in your home.  I once lived near a radio tower and it made my life miserable the second something was unshielded.  Not sure any of this will make a difference, but I think it is worth looking at.  No harm in trying to narrow that issue down.