Re: [LAU] ground loop hell

On 11/02/15 13:58, David Christensen wrote:
> On 02/10/2015 05:43 PM, Len Ovens wrote:
>> As an aside... I don't think I will need it at this point, The isolation
>> boxes that are easy to get are "DI" boxes tha go from high impedance
>> unball to low impedance bal. Would these still work to go from a
>> ballanced output to an unballanced input?
>
> DI boxes are designed to connect an unbalanced output to a balanced
> input. I've also pondered running DI boxes "backwards". From a
> technical view, I'd need to study the schematics of the driving
> equipment, the DI box, and the driven equipment to convince myself
> that it could work and not damage anything. I might try calling
> technical support. From a execution view, I'd need the right adapter
> cables (such as XLR-F to XLR-F). But from a conservative/ safety
> view, I'd rather hook everything up the way the equipment
> manufacturers tell me to and not have to worry about it.
>
>
>> Or do I need a one to one
>> isolator? Or does it depend on the powered monitor?
>
> I'd look in the monitor manual and follow the manufacturer's
> instructions. If you don't have a manual and can't get direction from
> the manufacturer, I'd use an isolation transformer with suitable
> connectors and cables.
>
>
>> How does this one look: http://www.rolls.com/pdf/M_HE18.pdf
>
> That looks useful.
>
>
>> Having "solved" my problem with a single power source, would it still be
>> worth while isolating all stage amps from the mixer?
>
> If the mixer has balanced outputs, the stage amplifiers have balanced
> inputs, and both are powered from the same supply, isolation
> transformers should not be necessary. I'd run balanced cables from
> the mixer to the amps and call it good. That said, good isolation
> transformers will cause a small lose of signal and fidelity, but they
> might provide protection for certain equipment failures or operator
> errors.
>
>
>> I think I will run
>> ballanced audio through the snake and do the cable adapting at the stage
>> end anyway.
>
> It is best to keep balanced signals in balanced cables for as far as
> practical.
>
>
>> Right now there is a TS plugged directly into a TRS mixer
>> output which means the signal minus is grounded.
>
> I wouldn't plug a TS cable into an balanced TRS output. First, you
> are shorting one half of the balanced driver output circuit. Second,
> you are injecting chassis ground noise into the audio circuits.
Agreed. If you run balanced -> unbalanced, it's probably best to run
shielded twisted core from the output and just leave the shield
disconnected at the input. It's discussed in those Rane docs I posted.
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Received on Mon Feb 16 04:15:03 2015