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Ground loop hum question.


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This isn't computer related, but as you guys seem a friendly and knowledgeable bunch I figured I'd try asking here. Just got a new amp and preamp (Kingrex QS-01 and kingrex pre-amp) and now have a nasty ground loop hum. Through some playing around, I've concluded that the ground loop is caused by the simple interaction of the amp and pre-amp. It persists even with everything else unplugged from the wall as well as the source itself unplugged from the pre. Whereas I can plug the source straight to the amp with no hum.

 

Right now my solution has been to lift the ground on the amp and pre using 3 to 2 pin cheater power plugs. Sonically this works great and I really like the amp and pre, but I'm a little afraid to keep this setup long term. Kingrex has been really great and have offered to replace the amp, but from my rather limited knowledge I'm not sure that this would help and would feel bad if they replaced a unit that had nothing wrong with it.

 

For any of the more knowledgeable forum members who might be able to advise: Could this be an actual fault in either the amp or the pre? Do ground loops point to poorly designed components? Other then a basic knowledge of differing ground voltages, I'm really at a loss as to the root of ground loop hum so any information to help me make a decision would be great. Thanks guys.

 

PS Audio Quintet > Powerbook (iphone with apple remote app) > HRT Streamer II > Kingrex Pre-amp > Kingrex QS-01 > Devore Fidelity Gibbon 7.1\'s

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These can be very frustrating to deal with. Aside from ground lifting your equipment (as you've done), there are two approaches. If you are in a permanent location, you should have an electrician with experience wiring sound studios provide you with a dedicated 20amp circuit with an isolated ground. The ground should NOT be connected to the same thing as the rest of the electrical system used for everything else in your house/facility.

 

A second approach is power conditioning. In general, power conditioners will degrade the sound signal, unless you choose a very good one. Look for one WITHOUT transformers or coils that are designed specifically for amplifiers. The filtering should get rid of the noise.

 

Sanjay Patel | Ciamara Corporation | New York, NY | www.ciamara.com

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Thanks for your comments and moral support so far. I've done some research and a lot of messing around already, so I'm mostly at the point looking to see whether from a technical standpoint kingrex replacing one of the units would likely do any good.

 

However, to provide some more info and answer questions. Right now everything is plugged into a ps audio quintet. I talked to paul over at ps audio and it doesn't seem like power conditioning does much for true ground loop hum (although I'm not sure if this would hold true for a regenerator like the premiere). It is just one of those really pesky issues, although usually seems to come from tv's and associated equipment, not simply the amp and pre alone.

 

I have, however, tested plugging them straight into the outlets and each straight into separate outlets (the latter of which did reduce the hum a bit, but obviously nothing like straight lifting the ground). And all my components have grounding pins, which as mentioned are lifted from the amp and pre right now to solve the issue.

 

None of the components have xlr, so it is all single ended rca. I suspect that going all balanced would eliminate this kind of problem, but the balanced components I would be interested in are all slightly out of my budget range. Also, I live in an apartment so wiring changes are out of the question, but maybe one day when I get my own place. ;)

 

PS Audio Quintet > Powerbook (iphone with apple remote app) > HRT Streamer II > Kingrex Pre-amp > Kingrex QS-01 > Devore Fidelity Gibbon 7.1\'s

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I have, however, tested plugging them straight into the outlets and each straight into separate outlets

Which outlets do you mean here? Somehow there is a voltage difference between the grounds of the amp and pre when the grounding pins are plugged in. Have you tried plugging both boxes into a single duplex outlet at the wall (bypassing the Quintet)? Do you get the hum when only the the amp and pre are involved? Does the hum level change with volume setting? Do these boxes have a separate ground connection?

 

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I have tried plugging both boxes into a single duplex outlet at the wall with nothing connected to the pre, the only connection being single ended rca from pre to amp (no source connected). I also connected them to two different duplex outlets which resulted in slightly reduced hum. The hum level does not change with volume. And the only grounding for both amp and pre is the ground pin of the power outlet.

 

PS Audio Quintet > Powerbook (iphone with apple remote app) > HRT Streamer II > Kingrex Pre-amp > Kingrex QS-01 > Devore Fidelity Gibbon 7.1\'s

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1. Reverse the orientation of one of the two cheater plugs. This may require filing down the wider blade of the cheater plug. Try the preamp reversed and the power amp normal, then vice versa. Caution: in any component having a metal case, the purpose of the ground connection is to protect you from electrical shock in case of gross breakdown within the power supply. A cheater plug defeats this protection. However, a cheater plug is perfectly fine if the component has a plastic case.

 

2. A much better solution is to use balanced interconnects. Depending on the design of the equipment, it can be impossible to eliminate hum with unbalanced interconnects.

 

Tutorials:

 

http://www.dself.dsl.pipex.com/ampins/groundloops/grndloop.htm

 

http://www.firstwatt.com/downloads/ground-loops.pdf

 

http://www.jensen-transformers.com/an/ts_guide.pdf

 

http://www.jensen-transformers.com/an/an004.pdf

 

 

HQPlayer (on 3.8 GHz 8-core i7 iMac 2020) > NAA (on 2012 Mac Mini i7) > RME ADI-2 v2 > Benchmark AHB-2 > Thiel 3.7

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one of the grounds in the wall outlets or the multi way outlets are faulty, loose or soemthing like that. If the pre and power amps have both 3 pin plugs, you can setup a hum, if the earths are different. I'd get an electrician to inspect the wall outlet wiring and other points in your place that may be the cause.

Lifting the earth connection of a piece of equipment that is designed to be connected to the ground is really dangerous, and you need to put this cable back again. Like right now.

It is also quite possible that the ground connection inside the amps is faulty. No need to go to XLR just yet and it wouldn't solve your problem.

 

AS Profile Equipment List        Say NO to MQA

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