ground-loop problems

Interesting, would have never suspected it; thanks for the heads-up.

Michael

What connectors do they use? There simply wouldn't be room for XLRs on the back of my AV amp.

With decent design, you don't ground at each component. You use the screen of the interconnect to ground everything back to the same point.

Even a small power amplifier has enough room for XLRs. Many control units (what used to be the "preamplifier") are huge -- mine has ten XLRs on the back, not to mention more than 50 RCAs, plus S and TOSLINK connectors.

I'm afraid to say anything, because I'm not an expert on grounding. But I'm pretty certain that what you're saying is wrong.

Simply connecting two amplifiers by cable shields does not cause the amplifiers' grounds to have the same AC potential. This is why components "far"/"near" each other, not connected/connected to the same outlet, sometimes/rarely have hum/buzz problems.

Well I meant a combined unit like most AV amps. An amp is an amp regardless of what it's used for. And 10 XLRs would nowhere cover the connections on mine - that is after all only 5 inputs before you even consider outputs, etc.

Works perfectly here. Even between two rooms which are on different circuits. But there is only one mains ground - that on the AV amp. I basically have a SCART cable running from the main system in the living room to the TV in the kitchen - mainly to avoid the different sound delays associated with watching even the same prog off digital through different TVs. The sound from that TV is fed into the audio system in the kitchen.

Not in the UK - unbalanced is the usual means of connection - and very rarely will everything be on the same outlet. The same circuit, though, most usually. But as I said, if you have a mains ground to every piece of equipment and a screen connection too you'll likely get an earth loop and hum - since most equipment has the metalwork connected to the signal ground.

I do remember some older Pioneer separates all fitted with three core mains leads and if you plugged them all to the same outlet via a splitter of some sort and used the supplied interconnects, you got an earth loop.

The issue -- in my mind -- is the distinction between "mains" (AC) ground and audio ground. They're not the same -- at least, not in the U S of A. This is why it's possible, on devices with three-wire power cables, to sometimes reduce the hum by lifting the ground on one and "rotating" the plug. Indeed, the Parasound power amps have a "ground lift" switch on the back.

I've spoken with Magnolia and Pioneer, and neither had the "Aha!" response I was hoping for. I'll call Parasound today and ask them.

If they're not the same there would be nothing to gain from an earth lift switch. It's having two non identical paths for the signal ground that causes an earth loop - you get a differential current flow. But as I said, it is common for them to be the same. But don't you have 'double insulated' equipment that doesn't need a safety mains ground? This is the norm for Hi-Fi equipment in the UK - even with the higher voltage here. And assuming it has the normal transformer supplying the DC - I'm not sure why reversing the mains lead should have any effect - given an isolating transformer of this type removes any reference from the supply - even when one leg of the supply is grounded as in the UK. Not so sure about SMPS, though, and they seem to becoming more common in audio equipment.

here.

Not that I know of. Only power tools (and similar products) are double-insulated.

This is common experience, not something I've made up. I'm sure other people in this group can report similar stories.

Could we agree to drop this discussion for the time being, until we can find a /real/ expert on grounding?

Right. Thank gawd I live in the UK, then.

It makes no sense, unless there is a direct connection between supply and the DC side. Last time I can remember this was with 'live chassis' valve stuff.

Fine. But I've certainly got enough 'experience' to know that balanced connections are total overkill for domestic line level installations. Different matter with low level signals from microphones, etc, or for very long runs.

If you've been sold that they're needed, that's your problem.

Well... Balanced inputs and outputs have been common on the "better" audio equipment for around 20 years. They're particularly desirable if you're a nut about fully balanced circuitry. And you pay for them whether or not you want them.

Balanced ins and outs became really popular with the introduction of the A/V system controller, precisely because they eliminate, a priori, grounding and hum problems, without adding a lot of money to the system's cost.

I previously owned Brand K electronics, which were fully balanced, and I never had hum problems. I could crank the volume all the way up, well past normal listening levels, and the system was dead-quiet (other than through the phono input). Why would I want to use unbalanced lines?

Balanced cables cost only a little more than unbalanced cables. Unlike RCA plugs (which should have been banned decades ago), they rarely pop loose, and you can plug and unplug them without getting a "big blast o' hum". *

• The better RCA cables have "long" collars, so the ground is made before the hot side when plugging in, and vice-versa when pulling the cable.

Plenty of the very good audio equipment doesn't have balanced inputs. They're completely unnecessary in the average domestic setup to avoid hum, etc.

So you say. I've got 'a very good' AV amp too with not a balanced connection in sight. Oh - and no hum.

Up to you but I can do the same with unbalanced.

Err, plugging and unplugging *anything* with the level control wound up is very bad practice - but if you don't care about your speakers and just want to prove some point or whatever, fine.

Oh - an XLR can't 'pop' lose unless there's something very wrong - they have latches to stop this happening. But that's because they are basically for microphone etc use where they will get strain on them. Unless you wave your amp round your head, not necessary in the home.

I guess you are forever pulling things apart and re-plugging? I don't have to - I have more than enough inputs for my needs. Something that simply wouldn't be possible if using XLR connectors. The amp would be bigger than the room...

This is precisely the kind of discussion I did not want this question to devolve into.

I don't understand why you think an audio system with components separated by 20' or more, and connected to different power lines, can be wired with unbalanced interconnects, on the naive assumption that there will never be any problems with hum or noise.

For what it's worth, all my prior systems had the power amps sitting next to the preamps. The components were connected with unbalanced cabling, and I never had problems with hum, noise, etc. Nor did it ever cross my mind that any of these systems would be "better" with balanced wiring.

My Parasound components -- and the Apogee electronic crossovers -- have both balanced and unbalanced inputs and outputs, and can be freely connected as desired. Other than the fact that balanced cables cost slightly more than unbalanced -- why would anyone in their right mind use unbalanced cables? Balanced cabling is in every way "superior".

I'm friends with the manager of the Bellevue Magnolia. I'll ask him what their installation department's opinion on this matter is, and /why/ they hold that opinion (whatever it might be).

That's one way to get hum pickup (voltage drop due to current flowing in a wire), but there's another: an actual *loop*, say unit "A"'s ground to the power line, power line to unit "B"'s ground, and unit "B" back to unit "A" via the shield of the signal cable (a real "loop").

That loop is a single-turn transformer winding, and if the three wires are arranged so the loop has an enclosed area (which is almost always the case), any magnetic lines cutting one of the wires differently from another will induce a signal into the wire of the loop -- that's why twisted pair works; the area enclosed by the wires is very close to zero.

That kind of hum problem is easily dealt with by transformer coupling the signal, because (not counting the impedance of the interwinding capacitance), there's no more loop to couple hum into.

Isaac

Because it is the common domestic way to do it. In the UK at least. You may well have to take care with cable runs to avoid picking up interference from mains wiring etc - but then the same applies to balanced circuits too, although they are more robust.

Well they can't be 'better' since you're introducing extra electronics to balance and unbalance the signal - not many devices are balanced internally.

You also have a balanced output radio tuner? Record deck? Etc?

Domestic equipment is fitted with balanced in and out because it looks professional. Or so it may be used in a pro application, as at the power amp side of things there is some crossover between them. But not really with AV stuff.

If your equipment is designed for balanced operation it's quite likely the unbalanced connections are an afterthought and the screen connected to mains ground. A simple check with a DVM would confirm this. If this is the case they ain't suitable for unbalanced connections directly. But that's their design fault - nothing to do with principles.

I'm not trying to deny that balancing is necessary for long cable runs - especially with low level signals, like from a microphone. Just that it's an unnecessary extra expense and complication in the domestic environment.

Yes- that's what I mean. Two bits of equipment where the audio ground and mains ground are common - like most domestic equipment fitted with a three core mains lead - and connected via a phono lead

With a balanced pair the signals are out of phase so any interference on the line is cancelled out when you bring it back into phase at the other end.

Yes - although removing one of the ground connections will usually work too. But as I said - in the UK at least - very few audio devices have a mains ground, with the exception of the power amp itself. They are Class II (double insulated) so don't need a safety ground. This has been the case for many a year. Otherwise you'd get a hum loop...

This is not correct. Changing the circuit from an unbalanced input or output to a balanced input or output does not add a gain stage.

The power amps were designed by John Curl, one of the "inventors" of full-complementary push-pull amplification. I will ask him what topology the Parasound A21 uses.

The tuner does, but I use the unbalanced outputs. We were talking about power amplifier connections, anyway.

This is common. It is not generally considered poor design.

BIG WHOOPS! I wrote that in a rush.

Balanced inputs are commonly converted to unbalanced by grounding one side -- to the SIGNAL ground (that is, zero volts in an amplifier with a balanced power supply), NOT the mains ground.

Don't forget about capacitive coupling between the windings in the mains transformer. Depending on transformer geometry, the coupling might be stronger to one mains lead than to the other. So it is advantageous to make the stronger coupled one ground.

Regards, Michael Karcher

Who said anything about gain? I said electronics. Usually done with just an IC these days. In its simplest form it just requires the correct transformer either end. But good transformers ain't cheap. But still the best way to provide a 'bomb proof' balanced circuit.

However, to conform to balanced audio standards it should also use the correct level which is rather higher than the usual unbalanced one found in domestic equipment - so may indeed require more gain somewhere.

It supports 1080p why else would it be there.