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Proper way to ground and loop breakers

dennnic

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Hi, I'm trying to get some advice and opinions from folks that have prior experience or have been educated in this area. Primarily from a safety standpoint.

I am building a simple active crossover and a power supply for it. It's positioned in a separate metal box, in-between a preamp and two power amps, with a dedicated mains connection.
Unbalanced interconnects only, unfortunately.


As far as I see it, three ways to prevent ground loops:

1. Keep the interconnects short and hope for the best (the simplest and safest way), where ground of all circuitry gets connected directly to it's chassis,

2. Use a loop breaker on the ground line between device's chassis and a crossover circuit (in reference to Rod Elliott's Earthing article on sound-au.com). Where one would connect preamp RCA cable ground (it's shield) to the crossover inputs and do the same for the output signal, or

3. Don't connect RCA cables' ground at all and leave it 'floating'. Instead, use chassis both for a safety ground and a 0 volt connection for signal on the crossover circuitry (where you would use ground from interconnect, that's actually coming from a preamp).
I've seen many people actually cut the cable shield on a receiving end and call it a day. What would happen to the audio signal if you use some other devices chassis for a reference 0v line, instead of 0volt line that's actually exiting from the DAC/preamp? With exclusion of RFI and EMI signal pollution.


What would you chose?

Best regards,
Stefan
 

Audiofire

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Hi, I'm trying to get some advice and opinions from folks that have prior experience or have been educated in this area.
Understanding, Finding, & Eliminating Ground Loops in Audio & Video Systems by Bill Whitlock

Bill Whitlock seems to be most interested in your options 1 and 2, but I can highly recommend to read the document if you haven't already.
 
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dennnic

dennnic

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Understanding, Finding, & Eliminating Ground Loops in Audio & Video Systems by Bill Whitlock

Bill Whitlock seems to be most interested in your options 1 and 2, but I can highly recommend to read the document if you haven't already.
Thanks for the suggestion, looks like a worthwhile reading, I will look into it.
 

sergeauckland

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I use a 1:1 audio transformer to break any ground loops. Safest possible way, with complete galvanic isolation between the two sides. It also has the benefit of being able to connect properly a balanced and unbalanced circuit. May be a bit more expensive, but works best.

S.
 
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dennnic

dennnic

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I use a 1:1 audio transformer to break any ground loops. Safest possible way, with complete galvanic isolation between the two sides. It also has the benefit of being able to connect properly a balanced and unbalanced circuit. May be a bit more expensive, but works best.

S.
Wouldn't a transformer stay in the way of stray/fault current reaching the circuit breaker panel?
 

sergeauckland

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Wouldn't a transformer stay in the way of stray/fault current reaching the circuit breaker panel?
No, because each item should be earthed individually or be double-insulated so should never ever rely on the interconnects for safety earthing. All the audio transformer does is give galvanic insulation between the two items whilst passing the signal. It can also be used to balance or unbalance signals between equipments.

Edit:- On rereading, I mean using an audio isolating transformer, not mains isolating.

S.
 

Audiofire

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Edit:- On rereading, I mean using an audio isolating transformer, not mains isolating.
Right, I remember looking at the Morley Hum Eliminator. But it has other technical problems like impedance, distortion and price. So should be considered a last resort obviously. Basically, the device is a compromise.

Especially AC mains isolation transformer is a compromise, avoid.

Details here:
 

sergeauckland

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Right, I remember looking at the Morley Hum Eliminator. But it has other technical problems like impedance, distortion and price. So should be considered a last resort obviously. Basically, the device is a compromise.

Especially AC mains isolation transformer is a compromise, avoid.

Details here:
Yes, the Morley Hum Eliminator is the sort of thing I mean. I made my own using Sowter transformers, so the price of the Morley is perfectly reasonable compared with the cost of a couple of decent transformers.

Edit:-I just measured my Sowter transformers, and at 2v output and 20Hz, 3rd harmonic distortion is -60dB and 5th harmonic -80dB. Even harmonics absent. At higher frequencies, distortion is progressively lower, so clearly transparent.
S.
 
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Audiofire

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Edit:-I just measured my Sowter transformers, and at 2v output and 20Hz, 3rd harmonic distortion is -60dB and 5th harmonic -80dB. Even harmonics absent. At higher frequencies, distortion is progressively lower, so clearly transparent.
Okay. I don't really know what I'm talking about sometimes, but read about it. It is said there is magnetostriction in transformers that can give distortion or something.
 

levimax

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Okay. I don't really know what I'm talking about sometimes, but read about it. It is said there is magnetostriction in transformers that can give distortion or something.
I have a DIY tri-amp unbalanced system and ground loops were an issue. I use one of these isolation transformers from Jensen https://www.jensen-transformers.com/home-theater/audiophile/ and it does the job perfectly and if you read the specs the distortion is vanishing low and only becomes a very slight issue at low frequencies which we don't hear very well any way. The only issue is good transformers are not cheap.
 

sergeauckland

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I would say impedance can still be an issue, low impedance is one of the most important things at least for a power amplifier.
What low impedance? The transformers go between the low impedance output of one device and the high impedance input of the other, so no impedance issues whatsoever. They're at line level not loudspeaker level or on the mains, so impedance is irrelevant.

S
 

Audiofire

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What low impedance? The transformers go between the low impedance output of one device and the high impedance input of the other, so no impedance issues whatsoever. They're at line level not loudspeaker level or on the mains, so impedance is irrelevant.
Yes, I was mostly just talking about the mains connection on a power amplifier.
 

tonycollinet

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One option you have, since you are building this PSU yourself. Don't put mains voltage directly into it, then you don't have to earth it to the supply. Use a simple isolated wall wart (or brick) PSU where the power to the crossover is not ground referenced.

That way at least you don't provide an additional path to earth which can cause additional problems. The crossover becomes irrelevant as far as ground loop is concerned (It can still continue the ground loop - just not add to it - No different than an RCA cable directly from pre to power)

If the sources, preamp and power amps are all located together, the chance for ground loop issues is small in any case.

If one of the sources is a PC, then go for an optical connection between that and the DAC.
 
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