ground-loop problems

I would like to read opinions on how to work around protective ground electrical codes which in my opinion are a bane to proper RFI and EMI suppression. I have needed to provide separate grounds (copper rods in soil close to the power and RF connections) for various receivers, audio systems, and instruments and have disconnected bypass capacitors inside the chassis(s) that were connected to the protective ground (third wire). In my experience, with so many smps and other switch mode devices on common AC circuits, the third wire is a noisy, un- redeemable nuisance, and is best eschewed for proper grounding schemes, but this often defies the electrical codes. Fortunately for me, I have located much of the sensitive gear in outbuildings that are not part of the common protective grounding requirement, and use proper grounding methods to reduce noise. In instances where the AC third wire ground is directly connected to the metal chassis, the only remedy has been to remove it and ground the device to a better ground and where possible, connect its satellite devices to the same ground or one nearby (in moist, highly conductive soil) to avoid serious ground loops. Sometimes, it is necessary to use heavy copper strap between ground rods.

If you have double insulated devices with only two-wire AC connections, then you are free to engineer a proper grounding system to prevent interference; perhaps using isolation transformers, in steel cases that are third-wire grounded, and disconnecting all downstream grounds from the third wire is worth a shot and still complies with codes (be sure that there are no bypass capacitors connected to the third wire).

Michael

One must suffer before enlightenment.

Buzz or hum? Measure the frequency. If you don't have any test equipment, use a PC software oscilloscope. I suggest:

If it's 60 or 120Hz, you might really have a ground loop. However, if it's some other frequency, then you might be picking up junk from some other source, such as a switching power supply, CCFL inverter, wall wart, or something similar.

I had a nasty buzz in my hi-fi stack that turned out to be the switching supply in my cheapo DVD player, coupling to the FM tuner through the plastic case (no shielding). I also fixed a low level buzz problem on my MIDI synthesizer when I replaced a switcher type wall wart, with a linear power supply. Later, I found that the power filtering in the synthesizer was inadequate.

Most home electronics get their case ground to the green (ground) wire of the 117VAC plug. If your home wiring system does not have a proper common (green) ground, then this line will have some 60Hz noise on it. By connecting the hi-fi to 2 seperate AC lines, you might be creating such a condition. Try everything on one AC line and see if fixes the problem. If it does, check your outlet and house wiring.

A really sloppy way to find the buzz source is to take an unterminated phono cable connected to a high gain Mic input, and save it around your equipment stack. If the noise source is radiating junk, the tiny end of the phono cable should pickup something.

I suggest that you:

1. Identify the buzz/hum characteristics.
2. Play with the grounds.
3. Attempt to identify the source.
4. Disconnect cables and boxes until the buzz goes away. (Diagnosis by substitution and elimination).
5. Sniff for a possible source.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Good grief. ;-) A bit OTT for the sort of runs involved in domestic situations.

I'm not sure about how the US does things mains wise - but in the UK pretty all equipment has an isolating transformer in the PS and is double insulated so no safety ground is needed - apart on usually the main amp or AV centre. So the only ground audio path is via the screen on the interconnect. Which should prevent any earth loops. However, I well remember some Japanese 'separates' where they did have (obviously at that time) transformers in the PS but also had all the cases earthed via the power cord - and that ground was the same as the audio one. Plug it all up using the supplied leads and you got earth loop hum...

However, if you've tried a proper mains isolating transformer, an earth loop is unlikely.

--
*Don\'t byte off more than you can view *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

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Have you tried putting everything on the same isolation transformer and running everything on long extension cords from the isolation transformer to the individual units. That way, you have eliminated ground loops. Then if that works ok, try bypassing the isolation transformer and run everything from the outlet the isolation transformer was plugged into, T way the ground loops still cannot occur, but you are pluggged into the house wiring. Then start moving things back into their normal mode and see if it is the blu-ray or maybe something else. Then play detective.

Huh? That does not necessarily eliminate ground loops (except perhaps in an ideal world). The devil is in the details (e.g. bypass capacitors, inter-device connections and their associated shields, downstream power strips, cable TV connections, etc.). Every system must be considered on its own merits.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam.  Our true address is of the form che...@prodigy.net.

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I ran into an audio hum problem but in my case it was 2 computers (1 to the TV) with antenna connection being the culprit. I also needed a 'float' on the cable feed. Here is what fixed it.

I bought 2 of those at $5 a pop. Money well spent.

G=B2

**Disconnect the antenna/cable connection from the system. That should do the trick. If it does, you need an isolator for the antenna/cable system.

--
Trevor Wilson
www.rageaudio.com.au

Apart from other good suggestions - if the buzzing sets in abruptly and shows hysteresis, I would suspect oscillation on above hearing frequencies. The loaded power supply would provide the hum (which is normally masked by very loud sound from the speakers).

--
 - Blarp the Enigmatic

I'd like to thank everyone who took the time to respond to my question. I was particularly appreciative of those that told me about noise & grounding problems I've never even heard of.

I'm not quite ready to put everything on one circuit. So I'm going to call both Parasound and Pioneer to see what insights, if any, they have to offer.

Again, thank you-all for your help.

PS: As for balanced cables being an OTT solution for home installations... I have five power amps, four of which sit next to the speakers they drive. Given the distances, and the fact that the amps draw significant current, and some are on different circuits, it would not be a good idea to use unbalanced cables.

I take it the Blue device doesn't have component out that you could try instead of HDMI?

It does, but... I don't think it supports 1080p. And even if it did, I'd still have a common ground, would I not?

This is not a major problem, just an irritation.

I dunno US electrics, but can't see why that would matter. As far as audio

- or video - is concerned there should be only one ground. And that doesn't really matter what mains circuit things are fed from as there will be an isolating transformer between it and the DC. Unless it's some crappy design where it has to be grounded for safety reasons.

What distances are you talking about? I have unbalanced runs here of some

80 ft without problems. I do use balanced audio to feed things round the house - but that is purely to use cheap telephone cable and avoid crosstalk.

--
*I finally got my head together, now my body is falling apart.

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Keep in mind that your balanced amps will not be balanced unless whatever drives them has balanced outputs. Your cable TV is a common culprit for introducing hum, etc. Use a 75 ohm to

75 ohm transformer or back to back 75 to 300 ohm matching transformers if the cable is adding hum when connected. For your unbalanced audio, a ground loop forms when current flows from one chassis to another chassis through the shield of your cable. You can use line level audio isolation transformers in those connections which will break the chassis to chassis connection. This will eliminate the need for swapping grounds or isolation transformers at the power side of things. Another option is to connect a heavy gauge ground strap from chassis to chassis in a star grounding scheme. The ground strap will hopefully provide a lower resistance path for the chassis to chassis ground currents rather than through the shields. This can work and is cheaper than converting to balanced, or using audio isolation transformers.

Keep in mind that most 'matching transformers' are autotransformers and supply no isolation.

to

Good point, I forgot about that! bg

Should be -- but isn't. Each device has its own ground. Each ground may have a slightly different AC potential. This is the cause of "ground loops" when you connct the devices.

All the equipment in my system is transformer-powered. That, in and of itself, does not prevent ground loops.

You're fortunate to have no problems with 80' runs. Professionals use balanced lines for a good -- it avoids problems.

Gee. I never knew. The amps and the controller are from the same company, and the balanced outputs of the controller feeds the power amps.

to

I am aware of this. I discovered it by myself 25 years ago.

I've had good luck with jensen isolators. However I just now went to look them up and see the price is now $49. Too damn high. I had remembered paying too much, but it was around $25-30.

Indeed.

In the UK pretty well all audio equipment has class II insulation - so doesn't *need* the metalwork grounded to a mains earth for safety reasons. And has been for many a year. So won't normally have a mains earth connected. If it did have you'd get earth loop problems - since the DC side is normally grounded. And that is connected to the co-ax screen. So the only ground connection is via the interconnect cable - avoiding earth loop problems. You can sometimes get this with using more than one tuner off an aerial DA - but not so usually with video equipment which is designed to be daisy chained off one aerial feed.

I'm a sound recordist working in TV so yes I know about balanced equipment. But its use is more for the common mode rejection of interference on long and hazardous runs - as well as to provide immunity from ground loops across a variety of equipment which is likely to be used in different situations. But shouldn't be needed in a domestic environment for a permanent installation. And such connections are rare in domestic equipment. And rightly so, since they add unnecessary electronics at both input and output - adding to complexity and cost.

--
*The hardness of the butter is proportional to the softness of the bread *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.