Balanced selector switch

[Freq Band]

This is a super easy question.....
I have one balanced input on my DAW monitor preamp.
I want to build a small (mechanical) "selector switch box" to swap between multiple inputs, and I don't want any "pop" when switching.

Make-before-break ?
Is "ground" (shield) included in the switching action ?

pic with the shield left unanswered...

=FB=

 

[Tubemooley]

Good question. I'm not sure about make-before-break. But I do know about ground. The answer is no. Do not switch the ground..... At least not for source switching. Ideally, all three boxes (two sources and one destination) are on one AC power circuit. 99% of the time they will all be grounded to the same AC power ground. If they are connected this way now without the source selector switch and there is no ground noise, then simply solder all three grounds together permanently. However, if your set-up changes in the future and one of the sources introduces ground noise, then you may have to lift the ground on that box. You could either un-solder wires or put a switch in there. But for the actual audio signal switching, you do not need to switch ground. DW.

 

[Samuel Groner]

I don't think there is a disadvantage when switching the shield too but the potential of ground loops when not. Although within a decent (balanced) system both should work well.

Shorting switches will short the two outputs together during switching, so perhaps a non-shorting might be more appropriate. But again actually both should work well.

However I don't think these things are particularly important regarding switching noise unless the amps/speakers are very sensitive. It's more a question about how much DC there is on the two outputs.

Samuel

 

[abbey road d enfer]

There are two sorts of clicks when switching:
a) Those that are due to residual DC/IC offset; this is irrelevant to you
b) Those that are due to the simple fact that you interrupt a signal at a a random point where its amplitude is probably not zero, and connecting to another, which is probably not zero.
So, if you switch only when signals are muted, there will be no clicks.
One could implement a zero-crossing detector, that would allow switching only when the switched-off signal is crossing zero, and switching the switched-on signal at its next transition.
Another solution involves the use of VCA's in order to provide crossfading instead of switching.
I strongly advice against make-before-break, because that would connect two outputs together, if only for a brief time, which is likely to create an even more disturbing phenomenon.
In a healthy installation, all shields should be permanently connected (although not necessarily altogether) and never switched.

 

[audiox]

When there is no DC present, the switching is very quiet (any DC from the balanced outputs and inputs causes troubles). You can solve the DC problem it by isolating the switch by capacitors and connecting all switch pins to ground with say 100kohm resistors.

Good signal relays are usually quieter than switches. I guess it is because of the faster switching and less contact oscillation. In practice switching noise less than -60dBu without signal can be expected.

 

[sodderboy]

Break before make because you do not want to short two outputs together, and do not switch the shields.  Connect each sides' shields together through the box (all your lefts together, all your rights together).  If you are shield lifted at the load equipment already you will want to connect through the box. 
I have built the opposite, relay switching for multiple monitor sets, and have had success with bussed shields.
Mike