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Need A/B speaker selector for 70V system.

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Shaun Kendall
Need A/B speaker selector for 70V system.
on Nov 8, 2017 at 3:40:11 pm

We are wanting to set up two different 70V sound systems at a location and most of the time, they will be independent of each other. But sometimes, we'd like for the speakers in system B to be fed from system A. The amplifier in system A is a QSC CX602V, which is bridged into a mono 1100W configuration. The amplifier in system B will be smaller.

Is there an A/B switcher that would work for this situation? Really, all I'd need is a simple switch that would feed the speakers in system B from either system B, or you flip it and they're being fed from system A. I don't think the switch would need any circuitry.

Thanks.


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Richard Crowley
Re: Need A/B speaker selector for 70V system.
on Nov 8, 2017 at 10:30:52 pm

Not clear if you are asking about switching the 70V distribution lines, or the inputs to the 70V amplifiers? Is there some reason why you can't switch the input to amplifier B?

The potential issue with switching the "B" 70V string over to the "A" amplifier is potential overload. You must establish how much load is on the "B string", and how much load is on the "A string" in order to determine whether you have enough reserve capacity in the "A" amplifier to handle BOTH strings.

Switching (or simply summing) the "A" program into the "B" amplifier would be a much safer alternative.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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Shaun Kendall
Re: Need A/B speaker selector for 70V system.
on Nov 9, 2017 at 2:58:36 pm

Hello Richard, thanks for the reply. The problem with summing the "A" program into the "B" amplifier is that they've already run speaker cable from the "A" system over to where the "B" system will be set up. I don't think they want to run a mic/line level signal over as well. From what I understand, we wouldn't be able to take that signal down to a level the "B" amplifier could accept as an input since it's already been amplified by the "A" amplifier.

We don't have an issue of overloading the "A" system. They actually removed two horn speakers from it when setting up the "B" system. It has a pretty large amount of room to play with, wattage-wise.

We could just cut the wires coming out of the "B" amplifier, the "B" system speakers, and the speaker wire coming from the "A" system, and put connectors on the ends to easily unhook the "B" system speakers and connect them to the "A" system, but I was hoping to find a switch so we didn't have to manually disconnect and reconnect speaker wires each time we wanted to switch.


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Richard Crowley
Re: Need A/B speaker selector for 70V system.
on Nov 9, 2017 at 3:43:40 pm

It is easy to convert speaker-level (including 70v down to line-level to feed into the B amplifier. The car audio people do it all the time. They have little attenuator gadgets available for really cheap.

To switch the 70v speaker line, you just need some sort of DPDT switch. There are dozens of different styles of switches, and thousands of choices. Nothing magic here. Be sure to switch BOTH wires of the 70V ine.

Note also that it is not good form to leave a power amplifier with no load attached. Another reason to switch (or mix) at line level rather than messing with the speaker lines.

I would still recommend to avoid switching speaker level circuits if at all possible. And it seems easy to avoid it.

---------------------------------------------------------------------------------
Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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Shaun Kendall
Re: Need A/B speaker selector for 70V system.
on Nov 9, 2017 at 7:14:18 pm

The only down-side to this is that it would require us to have the "B" system amplifier on whenever we want to have the "B" speakers fed from the "A" system. We were hoping to avoid that, hence the A/B switcher.

We would turn off the "B" system amplifier whenever the "B" speakers are being fed from the "A" system, so there wouldn't ever be the issue of having an amp with no load attached.


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