too much humm...why?

On Wed, 22 Jun 2005 17:39:37 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:

That is the point. Separate DC supplies that are of the "floating" variety are very hard to "balance". In each of these devices are DC supplies.

Reply to
TokaMundo
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And they are never "balanced". You aren't making sense.

Reply to
Floyd L. Davidson

You aren't making sense. There is no such thing as "balancing" DC supplies in different audio amplifiers.

Reply to
Floyd L. Davidson

I have never said it had to be placed away from the amplifier.

That indeed would be one place to have a common ground point. All that amounts to is a *short* ground run to that equipment, compared to the others. As long as it is then grounded via a significantly large enough cable...

Reply to
Floyd L. Davidson

It *is*. Typically at least #14 should be used between each equipment and the ground point. The common connection to ground must be something *substantially* larger (i.e., with a substantially lower impedance).

Reply to
Floyd L. Davidson

Standard terms makes discussion more sensible. "Injected noise" doesn't mean what you apparently think it does. "Injected" almost always implies *intentional*. (E.g., on a test bed system, you *inject* noise at test points...)

Reply to
Floyd L. Davidson

Of course they are hard to "balance", because that has absolutely *no* meaning.

Reply to
Floyd L. Davidson

On Wed, 22 Jun 2005 19:23:50 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:

All it takes is a 20mV difference to flood your audio signal with hum. Known fact for a long time among audiophiles.

Reply to
TokaMundo

On Wed, 22 Jun 2005 19:25:14 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:

The supplies do not get balanced. The high impedance inputs to audio amps do, however, need to be balanced with reference to the audio amp's chassis/zero reference, or 60 cycle hum gets introduced.

All it takes is about 20mV of difference to cause the problem, and all the AC line conditioning in the world won't stop it. It has to do with the line level outputs of the small signal sources compared to the line level inputs of the amplifier, and what both of them call "zero" volts. They have to be tied together at the chassis level, not the patch cord.

Reply to
TokaMundo

On Wed, 22 Jun 2005 19:28:13 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:

Exactly. And historically, the AMPLIFIER is the place to have said short run so as not to pick up any of your so called induced effects.

Size is not the issue. Reference point is.

Reply to
TokaMundo

On Wed, 22 Jun 2005 19:30:20 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:

Since copper wire is measured in ohms per thousand feet, I would say that even a #20 ga. wire is substantially lower in impedance than the steel chassis they get tied to.

It isn't some rack that needs a huge bar of copper running down the length of the frame. All that needs to be clamped is a 20 or so mV of a sub 150mV signal reference.

Reply to
TokaMundo

On Wed, 22 Jun 2005 19:32:59 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:

Not true. On a test bed system, one "injects" a test "SIGNAL".

Injected noise is most certainly a term used to reference a bad situation, and has been used for many decades.

Reply to
TokaMundo

The only talk of connectors is this thread was RCA connectors (which is likely what is used). RCA connectors use a signal conductor and a shield/ground - not ballanced. XLR (Cannon) connectors have 2 conductors and a shield/ground with the signal between the conductors - balanced.

A grouund loop results from 2 devices that 'want' their chassis to be at different voltages producing a current through the signal shield producing a voltage which is added to the signal.

If the chassis of 2 devices are bonded (particularly if there is a ground loop), the bond wire should have a much larger corss-section area than the cross-seciton of the shield conductors. #14 would seem to be a reasonable minumum.

The devices would best be powered from the same outlet. If they have grounded power plugs this is necessary.

If 2 chassis are bonded and the shield is disconnected from one RCA plug, the resistance between the 2 chassis is lowered (originally bond in parallel with shield) producing more hum which is added to the signal. If the chassis are not bonded, the voltage between them becomes what the devices 'want' which will be far higher than the original hum.

Steel chassis vs 20 ga wire - the copper wire has a higher conductivity but the chassis has a much larger cross-section and lower resistance.

Bud--

Reply to
Bud

A 20mV difference of *what*? You aren't making sense.

Reply to
Floyd L. Davidson

So why have you been talking about these floating DC supplies that have to be balanced? Regardless, the above statement is total nonsense. The "high impedance inputs to audio amps" is typically single ended, not balanced.

All the "balance" in the world won't either.

The "line level outputs" now, eh?

Reply to
Floyd L. Davidson

Wrong. Impedance *is* the issue. And the size of the cable is what counts. Any *common* ground has to be *low impedance*, which is the reason for the larger wire size at that point.

Reply to
Floyd L. Davidson

The Ohms per thousand feet refers only to the DC resistance, and is *not* a measure of the impedance of a length of wire. The inductance of wire goes up as the diameter of the wire goes down.

Likewise, things like sharp bends on the wire should be avoid, because that adds to the impedance.

A huge bar of copper would be an *excellent* idea! (And in commercial installations you might see exactly that.)

Reply to
Floyd L. Davidson

Cite?

Reply to
Floyd L. Davidson

On Thu, 23 Jun 2005 15:51:19 -0500, Bud Gave us:

The imbalance I refer to is one of the chassis potentials between the two units, not a balanced line.

D'oh!

Reply to
TokaMundo

On Thu, 23 Jun 2005 15:51:19 -0500, Bud Gave us:

No. A ground loop is caused by two chassis that DO have a difference in said potential. There ain't no *want* about it.

Reply to
TokaMundo

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