[IronLion]

So, I got a customized preamp from Gary Dodd not too long ago, a slightly modified ELP.  Plugged it in, and right away, running it into either my Signature 30.2 or my CIA D200's, there is hum.  It sounds identical to a ground loop, but the methods of fixing a ground loop do not seem to do anything to alleviate the problem.  I've tried removing the cable TV from the wall, even though it is in another room and in no way connected to my 2 channel system.  I've tried cheater plugs on my preamp, my power amps (the D200's), and both one of the D200's and the ELP at the same time.  I've tried all components into the same outlet.  I've tried unplugging everything else in the room and turning off every breaker in the apartment except for the one that powers my bedroom where the system is and its still there! 

I thought maybe it was a problem with the ELP itself, as the box was slightly damaged when I arrived.  I sent it to Gary Dodd to see if there was something wrong with it, and he replied and said in his system and his friends its almost as quiet as his battery-powered preamp.  So, does this mean that the hum problem I'm having is something inherent with my power line?  I can't seem to think of anything else, although I will say that I have used separates before (a Kingrex preamp with the D200's with no problem), and two other integrated amps before with no hum issues whatsoever.  What is going ON???  Does anybody have any idea?       

If its worth anything, I get hum from the speakers with the D200's and the ELP both on (whether a source CD player is connected or not), and in this case, with the D200's and ELP, the hum is apparent regardless of the volume level.  With the Signature 30.2 in the same situation, the hum is increased or decreased by turning the DACT volume control up or down.   

[heyeugenio]

Hey Lion,

I hate to say it but I've had similar problems with some tube gear that I've run before.  My home has got horrible power running to it.

I've got so many things on the same grid, outside of a dedicated line with a balanced conditioner etc. etc.
I don't think I'll ever have truly "black" background.

I found that with certain amps manufactured in the "Far East" I can get barely audible hiss and with others LOUD electrical and mechanical hum readily audible from my seating position.

I've tried pretty much every trick in the book from plugs, to shielding to humbusters and this and that with no luck.

After six months of exhausting investigation and a considerable amount of time, I sold a particular amp I received with regret.

I cannot blame all PRC or Far East products because some of the other gear manufactured there had ZERO hum.

If you get a chance, ask your local power co. to check your lines for faults.  If you can, bring your unit to a neighbor's house and install it in their rig (if you have anyone locally that you can test it with) or bring it to your local audio shop and have them take a listen.  It may be an issue in your area - just as mine is.

I brought some items to local stores that I have a rapport with and found that most of the time the items did not hum there unfortunately.

I just left it as dirty power to my home.  Hope this helps.

[richidoo]

Iron, sorry to hear you are having some trouble. Hum is a rite of passage for all great audiophiles. Some of us visit it multiple times seeking wisdom  My hum comes from FM antenna ground, but I was able to fix it.

Since the RedWine volume control affects the hum volume, the loop is in your signal line. Try a Jensen isolation transformer on the interconnects. It is model CI-2RR "stereo audio isolator". It costs about $150.

If you are shy about buying the Jensen gold without knowing for sure, you could try either of these junkers to test if it is indeed signal ground loop, or maybe you can find a used one on a pro-sound classified, or ebay.

If the IC transformer cures, then the signal ground on one or both units could be connected to safety ground in one or both. Some people disconnect safety from signal grounds, but I wouldn't challenge the designer's judgement, especially if Jensen solves it. Jensen makes quality stuff, and it is very transparent. Maybe the ART unit is decent too. I have used Jensen cap isolator on my FM antenna with perfect result, after parts express version crapped out, but it worked long enough to diagnose.
Specsheet
Review (loads slow)

Another isolation transformer from Lundahl: http://www.audioxpress.com/reviews/media/galo2872.pdf but I think you have to DIY?
Good luck,
Rich

[IronLion]

Thanks richidoo and heyeugenio for responding.  I looked up the CI-2RR "stereo audio isolator" and it looks like I will need to add another pair of IC's if I go that route right?     I'd rather not...maybe I'll end up selling the pre if thats what the problem is, I'm hoping to get a RWA Isabella when Vinnie finishes it anyways so hopefully the same issue won't exist there. 

I sent Gary Dodd another email to see if he knows how I might go about fixing it, its odd though, he hooked up my ELP in his own system and in his friend's and neither of them had any hum like I'm experiencing.  Maybe its just a bad match of gear?   

[SET Man]

Hey!

   Did you have this problem with your previous pre?

   If not then it is likely that your new Dodd ELP is making the hum.
 
   Have you try hooking up the ELP in other system?

   Anyway, my Audio Note M1 tubed pre hum a slightly but I only notice this when I'm right next to the speaker. This also depend on tubes too a bit.

   Don't know what speaker you have but this problem will get worse on speaker with higher sensitivity.

    If the hum in your system is very bad with this pre and the manufacturer said it work fine than maybe it is time for a new pre?

   Well, good luck.

Take care,
Buddy

[IronLion]

The only other pre I've used was a Kingrex Pre, and it worked fine with no hum at all. 

I'm wondering, would the wire method (connecting the two chassis' with speaker wire) work for this problem?  Its worth a shot I guess...

[richidoo]

The Sig has the same problem, and is battery powered? I don't know if it will still run with mains connection, but if so, and the hum persists then it is not a loop with mains, which is why cheaters did nothing. Plugging into power strip would cure it if it was a loop through neutral or safety ground. I would guess it is the pre transformer's magnetic field inducing hum in a signal wire or tube closeby. Preamp chassis needs to be BIG to separate the noise from the sensitive circuit. Maybe that's why Dodd went to battery design?  In some systems -70dB noise floor preamp is acceptable. But with high efficiency speakers and high gain amp that is still too loud. You can try a different tube, or sheilding the transformer if the layout makes it easy. But SETMan might be right - the pre might be happier in a less revealing system where the hum won't be as noticable. Be sure that the magnetic radiation is not coming from another component that is too closeby, like power amp. Move them apart to be sure blame is in the right place. D200 is toroid which are usually quiet, and is in a fully shielded box anyway. Sig is battery so no problem there. Maybe a TV or source transformer nearby?

If it is from transformer inductance, the Jensen would not help. Only good for breaking ground loops.
Good luck lion
Rich

[IronLion]

Richidoo, the thing that makes me doubt that it has to do with transformer-related interference from the pre is that Gary designed my ELP with an outboard power supply, so that the transformer can actually be set a ways away from the rest of the circuitry.  The transformer is only connected to the preamp by an umbilical that is about 4 feet long, so its design should minimize all noise and apparently in Gary's system it did this quite well.  The Sig does have the same hum issue with the ELP even when its not connected to its own charger, so you're right I guess the problem has to be signal related and not power related.  Still though I have no idea how to fix it other than maybe those IC transformers... 

[Wayner]

So if I understand right, the ELP is powered by a "wall-wart", is that right? If so, a "wall-wart" is a step down transformer taking the line voltage from 120 to 24 or 12 volts. Transformers create a magnetic field that can induce hum into poorly shielded interconnects. Is the wall wart close to any interconnects?

Wayner

[gstraley]

Iron Lion,
   Try swapping out some interconnects with other ones. I have seen where someone goes to replace a piece of gear removing the interconnects in the process. In doing so they may have inadvertently broken the ground on the IC itself. With some interconnects if you twist them when you take them off you can put a lot of stress on the solder joint causing the ground to not be attached anymore to the RCA connector. For testing purposes any kind of IC will work. If the hum goes away you know that you have a problem with one of the IC's. I have heard a couple of Gary Dodd preamps and none of them made any noise in 3 of the systems that I heard them in. Good Luck

[AphileEarlyAdopter]

I think, the problem is the source and the preamp and the amp are seeing different 'grounds'. The preamp should have a separate ground connection. If not, connect the ground from your source to the metal body of the preamp (and hopefully you are source and the amp have ground connections in their power cord and are connected to the same outlet). I think this is the reason you are hearing the hum even though all components are plugged into the same outlet. I suggest getting a good quality power strip (from www.b-p-t.com or www.cablepro.com).
If you still have a hum, there might be a DC component in the power supply, which needs to be taken care of using some 'humbuster' kind of devices. Or some isolation or balanced transformers in the power supply chain would do the trick.