ground-loop problems

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'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.

> 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.

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.


>> 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.

> 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.

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

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

> 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.

I've never experimented with single-ended and balanced installation, using
the same equipment, so I can't speak from experience. However, balanced
inputs and outputs have become common in "good" equipment, partly because
they add little to the cost, * and partly because -- especially in A/V
systems -- they make things easy for the manufacturer and dealer.

In a system where the amplifiers don't sit right next to control unit (qv,
my system), the designer & installer don't have to worry about hum and
interference. The customer isn't going to be happy if the dealer has to do
extensive troubleshooting to get rid of noise, or (worse) if the house has
to be rewired to reduce the inter-component ground potential.

I remember, ca 1978, installing a relatively simple Crown system in an
equipment rack. We had all kinds of grounding problems. Some of this was
probably due to the Crown equipment itself (surprising, because the same
products were used professional), but we wound up have to completely isolate
the units from the rack. This involved wrapping the screws in vinyl tubes,
and using faucet washers to lift the ears away from the rack. Our first
attempt used black washers, which contain carbon and are conductive. These
were quickly replaced with non-conductive red washers.

* Nor are there any additional electronics.

"Dave Plowman (News)" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> In article <h0mqkb$gl4$(E-Mail Removed)>, William Sommerwerck
> <(E-Mail Removed)> wrote:

>> I've never experimented with single-ended and balanced installation,
>> using the same equipment, so I can't speak from experience. However,
>> balanced inputs and outputs have become common in "good" equipment,
>> partly because they add little to the cost, * and partly because --
>> especially in A/V systems -- they make things easy for the manufacturer
>> and dealer.

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

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.


>> In a system where the amplifiers don't sit right next to control unit
>> (qv, my system), the designer & installer don't have to worry about hum
>> and interference. The customer isn't going to be happy if the dealer has
>> to do extensive troubleshooting to get rid of noise, or (worse) if the
>> house has to be rewired to reduce the inter-component ground potential.

> 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.

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.

<lots of interesting stuff snipped>

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.

>> 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.

> 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
> tje norm for Hi-Fi equipment in the UK - even with the higher voltage
here.

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


> 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.

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?

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

> 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... <ahem> 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.

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).

>> 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.

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

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.


>> 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".

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

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


> 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.

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

>> 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.

> 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.