Need help eliminating audio hum

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d3

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Need help eliminating audio hum
« on: 25 Dec 2015, 02:31 pm »
I recently upgraded my early model Stratos amp and Tempest preamp for a new Kismet-in-Stratos case and Tempest Extreme preamp (beautiful workmanship on the cases, BTW).  With the new components installed, I have a 60 hz hum coming from my speakers.  All components (amp, preamp, TT, Oppo, tuner and small monitor) are connected to a single surge protector, which is connected by a three-prong connector to the wall socket.  If the amp is turned on, but the inputs from the preamp are disconnected, the humming stops.  When I connect one channel from the preamp to the amp, no humming. But when I connect the second channel from the preamp to the amp, the humming begins in both channels.  This happens even when the preamp is turned off, even if the preamp is unplugged, and even if all of the inputs to the preamp are disconnected.  I have swapped a couple of pairs of ICs, including Groneberg and Audioquest, but get the same results.  So the problem appears to be coming from the preamp.  I’ve played around with the ICs a bit, to see if the metal contacts are hitting the case, but I can’t get the hum to go away.   Another issue, that may be related or not, is that if I turn the preamp off while the amp is on or still has power from the capacitors, I hear several loud pops from the speakers (not good).   This sounds like a ground loop, but I don’t know how else to get rid of it.  Any suggestions would be welcome. 

Happy holidays to all.

Wayner

Re: Need help eliminating audio hum
« Reply #1 on: 25 Dec 2015, 03:27 pm »
How many of the system pieces have a 3 prong plug? More then one means a ground loop is certainly at work here.

Wayner

avahifi

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Re: Need help eliminating audio hum
« Reply #2 on: 25 Dec 2015, 03:33 pm »
The turn off pops are likely turn off transients generated by the preamp and have no connection with the hum issue.  A modern preamp should have built in turn on and turn of transient suppressors.

Try plugging the preamp in to a separate AC source and see if this helps.

Frank Van Alstine

paul79

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Re: Need help eliminating audio hum
« Reply #3 on: 25 Dec 2015, 03:43 pm »
+1 to above. Just moving the preamp to another outlet will likely cure it. Yes, even if it is on the same circuit, it may be enough to eliminate or at least reduce the loop.

d3

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Re: Need help eliminating audio hum
« Reply #4 on: 26 Dec 2015, 02:12 pm »
Thanks everyone.  The amp and the preamp (and most but not all of the other equipment in in the system) use 3-prong plugs.  I've tried moving the preamp to one outlet and the amp to another and disconnecting everything else, but I still get the hum.  FWIW, most articles I found on eliminating ground loops say that the hum is caused by voltage differentials in the lines feeding the different components and that you should have the components on the same line, not different ones.  In any case, connecting the amp and preamp on the same outlet and connecting them to two different outlets doesn't change the result: 60hz hum coming from the speakers.  I agree that the popping noise that occurs when I turn off the preamp is almost certainly unrelated to the hum, but I mentioned it in case it gave a clue to the cause.  Interestingly, these new components are in the same system, attached to the same outlets, as my prior, Odyssey equipment which didn't cause the hum (I'm a long-time customer).  Is this an internal problem, such as improper shielding? Any user-implementable suggestions to try to fix this?   

Peter J

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Re: Need help eliminating audio hum
« Reply #5 on: 26 Dec 2015, 03:04 pm »
Two possibilities you might try to troubleshoot. If there's a cable TV hookup in the mix disconnect and see if that affects hum. A nearby receptacle is likely on the same circuit. Try temporarily running an extension cord to a know different circuit, meaning not on same breaker.

Folsom

Re: Need help eliminating audio hum
« Reply #6 on: 26 Dec 2015, 04:17 pm »
Does it not matter what source is plugged in as a single item being plugged into the preamp? That's important. If you plug in your CD player and nothing, then plugging in your DAC-streamer/phono/whatever it happens, and the reverse is or isn't true will tell us something as well.

You can use a 3 to 2 prong adapter to check if it will eliminate the hum, but this isn't a wise permanent solution anyone here is going to recommend (because the manufacturer used a 3 prong since their isolation isn't what's required to warrant 2 prong for the appliance; which is perfectly fine but isn't the case).

Wayner

Re: Need help eliminating audio hum
« Reply #7 on: 26 Dec 2015, 06:03 pm »
Unless you are running your equipment on wet concrete, there is no problem with using cheater plugs. I would ground one component with its normal, 3-prong plug and put cheaters on everything else. I'm pretty sure your hum will go away. I also believe that everything should be connected to the same power strip>same outlet.

Here is my vinyl room and everything is eventually plugged into 1 outlet. Of course, if I turned everything on, the breaker would trip, but only one system is on at a time (one amp, one preamp, one source (fm, table)). 3 of my components have a 3 prong plug, 2 have the defeat switch turned on. There are actually 5 systems here (amp/preamp/many sources each).



Wayner

audioengr

Re: Need help eliminating audio hum
« Reply #8 on: 26 Dec 2015, 07:01 pm »
Many different things can cause this:

1) your AC outlets may be wired backwards - check with a checker or manually
2) Use the same outlet for amps and preamp
3) the amps may not be properly earth-grounded - check the chassis to the outlet ground pin with an ohmmeter
4) a ground-loop may be causing the hum, but it may not be the preamp ground-loop.  Try unplugging preamp to see if it goes away, try unplugging source component to see if it goes away one at a time
4) it may be your connection to cable TV.  This ground is different than earth ground.  You may need a transformer in the coax cable to isolate the CATV ground and your earth ground
5) if it is a ground-loop and you cannot stop the hum, then you may need an isolation transformer between the preamp and amp.  I have excellent ones available, but they are not cheap.  These don't compromise SQ.

Steve N.

Johnny2Bad

Re: Need help eliminating audio hum
« Reply #9 on: 26 Dec 2015, 07:08 pm »
Ground Loops can be problematic. You are going about it more-or-less correctly (work your way back from output to input). Typically there is a cable or AC line that is part of the problem (forms one leg of a loop). Sometimes you can't really remedy the situation if the issue boils down to the internal ground structure of a component.

Member audioengr makes a good post with the troubleshooting procedure outlined comprehensively.

However, there is one sure-fure way to fix your issue, should you run out of hair to pull out. Use an isolation transformer of sufficient quality to be audio grade. I recommend Jensen transformers ... if you're handy you can construct a box yourself with your choice of connectors, etc (they are passive devices, so relatively simple to deal with ... choose the transformer wisely and keep leads short).

Alternately a ready-made solution with the correct transformers can be purchased. For your application, a Jensen Iso-Max isolation transformer placed between the preamp and power amp should eliminate all hum issues. The Jensen products are of high quality physically and sonically.

Be sure to purchase from a vendor that accepts returns, should you find you need one between all your sources and the preamp (unlikely, but not beyond the set of possibilities ... ground loops are unique and system dependent). In that case it might be worthwhile to explore cable substitutions, and assess the results vs the Iso-Max solution, or a combination. There is also the possibility that you may find a sonic penalty you can't live with, although I would say in my experience that isn't usually a huge issue provided you are dealing with a quality transformer manufacturer and an appropriate version.

Having said that, I am quite confident the one unit between the pre and power will work in almost all cases. Jensen make a number of variants (mono, stereo, audio, video, RCA, XLR, 3.5 and 2.5 phone, etc). You probably want the CI-2RR model. About $US 150, and note that they are sold to both the Professional and Consumer markets, so you can price check with Music Stores as well as Audio or A/V vendors.

Isolation Transformers work because a transformer can be constructed to pass AC of specific frequencies but inherently block DC. Although AC hum is at line frequency and various intermodulations and harmonics of that frequency, the connection that is the root cause of the ground loop is a DC loop.

There are those who are suspicious or outright dismissive of transformers in the audio chain. The takeaway is a given transformer requires high quality copper (typically, could be silver or gold for that matter, but ... well ... ) and other metals, which cost money in a fairly rigid and unavoidable way. In other words $$$ = quality and performance, and there isn't much else to add in that regard. They are what they are, and you most certainly get what you pay for, no way around it (for new construction).

Not sure if it's useful to you, but it's worth mentioning: optical cables break ground loops, so that is also an option with digital interconnections.

http://www.jensen-transformers.com/product/ci-2rr/

Johnny2Bad

Re: Need help eliminating audio hum
« Reply #10 on: 26 Dec 2015, 07:27 pm »
mmm ... I see the MSRP has changed to $US 200 from the $US 150 of about a year ago. Worth it, in my opinion, but maybe spend some time looking for New Old Stock (NOS) at the old price. One thing to check, though, is I don't recall the versions I last looked at the specification for to mention a Mu-Metal casework. If that's a feature only found on the current production, I would say it's a worthwhile improvement and probably justifies the higher MSRP.

JackD

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Re: Need help eliminating audio hum
« Reply #11 on: 26 Dec 2015, 07:38 pm »
Why don't we just ask Klaus since you say all you did was take out two Odyssey products and replace them with two more. If you did not change anything else then he may have an answer. To me the answer lies with the Tempest. You may with his guidance or Alex's be able to open the Tempest and find something that came loose in shipping. Oh, and the Kismet needs to go straight to the wall and not into a consumer grade power strip.

GentleBender

Re: Need help eliminating audio hum
« Reply #12 on: 26 Dec 2015, 09:16 pm »
I doubt it, but make sure if you are using a MM cart that the preamp is not set to MC. Just something easy to check.

sfox7076

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Re: Need help eliminating audio hum
« Reply #13 on: 27 Dec 2015, 01:13 am »
I had a recent issue that is similar.  Mine turned out to be in shielded interconnects.

d3

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Re: Need help eliminating audio hum
« Reply #14 on: 27 Dec 2015, 02:35 pm »
Thanks everyone for their suggestions (the internet can be a great thing, no?).   Here's a bit more information.  This is a dedicated audio system.  No TV involved anywhere, so I can rule out what appears to be a common source of hum in AV systems.  I'm using shielded ICs and swapped a pair (Groneberg for Audioquest) to see if that made a difference and it did not.  The hum begins when the preamp is plugged in, although it is not affected by the volume control on the preamp.  As for further action, here's what I'm now thinking, as I've run out of other ideas.  (1) get rid of the surge protector for the Kismet-in-Stratos and plug it into a high-amp extension cord (it won't reach directly to the wall socket).  (2) If I can get a hold of Klaus, maybe he can talk me through opening the Tempest case to see if something came loose in shipping.  He had it on his bench for a week before he sent it burning it in, so maybe something happened later.  I think the Tempest is likely to be either the cause, or at least the cure of the hum.  But as we all know, Klaus is a busy man these days.  (3)  Try placing a Jensen CI-2RR between the preamp and the amp.  I have to say, this last approach makes me worry about the sonic impact of adding another pair of cables and a transformer in my signal path.  Klaus, if you're reading these, do you have any thoughts about using an isolation device between the amp an the preamp? 

Regards, 

avahifi

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Re: Need help eliminating audio hum
« Reply #15 on: 27 Dec 2015, 04:15 pm »
Try this as a low cost experiment:

http://www.amazon.com/dp/B000KUD2G4/?tag=googhydr-20&hvadid=42092954016&hvpos=1t2&hvexid=&hvnetw=s&hvrand=16698627029480195649&hvpone=24.99&hvptwo=38&hvqmt=b&hvdev=c&ref=pd_sl_3971vo3har_b

Note that you will need four phone jack to rca jack adapters as the inputs and outputs are 1/4" mono phone jacks only.

This inexpensive little box is transformer coupled in to out so a ground loop hum path is eliminated.

Its bandwidth and distortion looks very good on my distortion analyzer so it likely will have only a minor impact on your music.

And, of course, it it works then a much more expensive and higher quality Jensen or Lundahl transformer will work too.

Frank Van Alstine

hifi12002

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Re: Need help eliminating audio hum
« Reply #16 on: 28 Dec 2015, 10:26 pm »
Give Klaus a call.

audioengr

Re: Need help eliminating audio hum
« Reply #17 on: 28 Dec 2015, 10:42 pm »
The transformer isolation device should fix the problem, but it will impact the SQ unless you get a much better one than mentioned.  Whatever your pocketbook will withstand. :wink:

d3

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Re: Need help eliminating audio hum
« Reply #18 on: 29 Dec 2015, 05:00 am »
I've tried plugging the amp directly into the outlet and not through a surge protector.  It did not affect the hum.  I get hum out of the speakers even when I disconnect every other component from the power strip, including the preamp, and even when I remove all inputs into the preamp.  As long as both outputs from the preamp are connected to the amp I get a 60 hz hum.  I don't see how this can be caused by a ground loop if I still get hum with only one component in the system plugged into the electricity.  Somehow the preamp is picking up hum and transmitting it to the amp.  Is this a problem with the preamp?  I'm prepared to try an isolation transformer, but if those only work to get rid of ground loops, I'm not sure that will help.    What is the consensus on the SQ impact of a Jenson CI-2RR?  I can afford $200 for this, but don't want to invest in some other devices that claim to eliminate hum that cost more than the preamp. 

Folsom

Re: Need help eliminating audio hum
« Reply #19 on: 29 Dec 2015, 05:38 am »
There must be a broken ground (return) connection on the preamp or amp, is what I assume atm. In fact I'm almost sure of it at this point. BTW if it is a broken ground then no transformer on this planet will help. It's easy a broke RCA jack, the wire going to the circuit board from it/connecting RCA jacks together, or an interconnect.

Why buy parts when you don't know what's going on?

When you say both outputs do you mean both channels? Because before I thought you mean two pairs of R and L outputs.

Do you have a multi-meter? It's a simple thing to diagnose if you can understand the beeping noise one makes when it has a connection.