Ground lift switches

[AndrewT]

sort the problem.
Don't put on a sticking plaster.

I think it is Whitlock that has published a hum detector circuit for detecting the PIN1 problem. I would think (not being a PA roadie) that every PA person will have the hum detector in his/her pocket.

 

[Enzo]

I'll say this and move on.

If you are faced with a stack of gear to set up as a system, and encounter a ground loop. Will you tear apart the equipment and reconfigure the grounding therein? Or will you use a ground lift externally? The OP was about a patch panel after all, which implies concerning one's self with connecting gear together.

As a professional touring sound man, I did indeed carry all manner of tools to detect problems. But it is not sufficient to detect problems, you also need to be able to correct them in the field. SO I also must carry a bunch of things like ground lift cables, as well as phase reversal adaptors, various balanced line pads to tame hot signals, and adaptors to convert most any connector to most any other. I can't tell the band "Gee, this gear isn't made right, sorry about the hum." I have to provide good clean sound free of hum.

 

[AndrewT]

Yes, and having detected the piece of defective gear you then use your spare balanced cable that is clearly marked "cap coupled screen" on one end. Conventional Chassis coupled screen at the other end.

As far as I know that is the "normal solution for the PIN1 problem. There are probably others.

But if one is building a bit of kit then one does not build in a PIN1 problem, one builds it right.
To me post1 sounds like he is building a patch bay. He won't need to incorporate a ground lift switch if he uses Chassis connected screens.

 

[Jsixis]

I like enzo have to have every connection possible because the average musician doesn't have a clue and many older amps have polarity switches so polarity is always a problem.
That said, everyone should read this which I consider the most accurate way to wire things.

Sound System Interconnection

 

[tinitus]

That said, everyone should read this which I consider the most accurate way to wire things.

Sound System Interconnection

cool

btw, instead of swith, and/or wire internally, I made this simple 'XLR-jumper' to create the single ended connection

any problems doing so ?
is it ok, or should I better mount that switch

I doubt I will ever run it balanced
but you never know
should I ever go buy a parametric EQ, I guess it probably better be a balanced

 

[AndrewT]

Tin,
Pin1 should be connected to Chassis.
Pin3 (Cold) should be connected to -IN (for Receiver), or -OUT (for Source)
It is not wise to short these two together.

 

[tinitus]

Tin,
Pin1 should be connected to Chassis.
Pin3 (Cold) should be connected to -IN (for Receiver)

I expect they are, internally

It is not wise to short these two together.

why not ?
(it is input on a classD power amp)

is it not normal procedure connecting balanced negative to ground on input, when doing single ended to balanced preamp signal ?

mind you, I cannot connect a balanced signal when the jumper is in

 

[AndrewT]

Audio ground is not chassis.
Balanced uses chassis for pin1, or it should.

The cold (pin3) if used as an audio ground is NOT chassis.

If you want to connect an unbalanced impedance Source to your balanced impeddance Receiver then the cable should be balanced to reject/attenuate interference on the cable.
The Source gets the conversion where audio ground gets connected to screen (pin1) and to Pin3 to feed along on wire to the receiver's pin3

 

[tinitus]

... the cable should be balanced to reject/attenuate interference on the cable.

ah, interference
don't know how much that worries me

sounds like you try to say pseudo balanced cable

 

[AndrewT]

Is that what Rane and Jensen tell us, when they suggest a converter cable? Keep the balanced for as much as possible. That must include the cable attached to the balanced impedance Receiver.

 

[tinitus]

noted, thanks

I will try with pseudo balanced RCA to XLR cable

and just have the other inputs as 'optional' with jumper, in case I'm missing a cable, or whatever might happen

time will show if makes any difference

anyway, I have planned to have instrument Jack input on front panel, with a buffer
back panel XLR input is only for extern preamp, or other units

 

[tinitus]

I also planned to have a XLR/Jack combo

but that Jack is also balanced
so that will need som caretaking too

 

[tinitus]

Is that what Rane and Jensen tell us, when they suggest a converter cable? Keep the balanced for as much as possible. That must include the cable attached to the balanced impedance Receiver.

Andrew, its a single ended signal going into a balanced receiver

I do not see how to 'keep balanced signal for as long as possible'

 

[AndrewT]

The balanced input receiver is expecting a balanced impedance signal. Use a balanced cable to maintain the balance to as early as the system will allow.
Use the conversion at the output of the unbalanced source.

 

[tinitus]

The balanced input receiver is expecting a balanced impedance signal. Use a balanced cable to maintain the balance to as early as the system will allow.
Use the conversion at the output of the unbalanced source.

yeah, ok ... but it's not getting any balanced signal, either way

sounds very 'theoretical', but I will try it, sure ... but not expecting much difference, if any

if I remember it I will report back about it

thanks

 

[tinitus]

hmm, I have always found that pseudo balanced single end cables sounded best with shield connecting to preamp

but only tried it with single end to single end, and never with RCA to XLR

but in the linked Rane paper, the shield is left floating

is that what a ground lift switch is doing ?

 

[tinitus]

so, if I insert a mono/instrument jack plug into the balanced XLR/jack combo, it will automaticly short pin 1 and 3

so, a ground lift switch on XLR pin 1 would 'route' the single ended ground to XLR pin 3

 

[turk 182]

wow it seems there's a lot of confusion about balanced lines and grounding practices.heaven forbid we start complicating matters with phantom power or A/D on balanced lines and maybe some high speed data too!
i guess i'm prone to mentioning phantom power and ground lifts because i've been there when some overzealous roadie starts flipping ground lifts with audio on and finds the phantom powered mic! many a horn driver has gone to speaker heaven in this circumstance.
when it comes to ground"lifting" anything exercise caution! an improper "ground lift solution" can jeopardize human life!

 

[tinitus]

well, many DIY'ers here couple the chassis and 'signal ground' via a resistor, diode, or thermistor

and some ground lift switches does that in the 'lift' position

but I 'out there' you never know what weird stuff comes your way