On Sep 2, 2005, at 7:39 PM, Dan Dugan wrote:
> Lou Judson wrote:
>
>> Thanks for the description, Dan. Makes perfect sense! Does it also
>> mean if wired unbalanced it does not matter if pin 3 is grounded or
>> unconnected? Would one or the other way have better noise
>> performance?
>
> It doesn't matter, but I would always make up unbalancing adaptors
> with pins 1 and 3 grounded, in case a transformer source (balanced
> and floating) is connected.
I do! Just wondered...
>
>> And this may be wandering off topic, but dbx 150X NR units specify
>> that if wired unbalanced, the ring (of its TRS output) must be
>> unconnected, not shorted to ground. Why might that be, since you can
>> describe ciruits for the non EE types such as myself... reply
>> offlist if this is too far off the topic. The dbx is the only thing
>> I have seen that says to do that.
>
> That's an example of what I referred to as the complications of
> unbalancing an active-balanced circuit. If it's just two out-of-phase
> amps driving pins 2 and 3, then grounding pin 3 will short the output
> of a driven amp. That may stress the circuit, and it may couple
> distortion through the power supply.
>
> It can be solved by what's called a "cross-coupled" scheme, but
> source impedance balancing is so much simpler, and cheaper, and more
> reliable. I learned it from Sound Devices, BTW.
Interesting! Thanks.
<L>
>
> -Dan Dugan
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