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.
>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.
-Dan Dugan
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