Speaker selector, OK for amp? - diyAudio
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Old 3rd August 2015, 04:11 PM   #1
Tinyker is offline Tinyker  Belgium
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Default Speaker selector, OK for amp?

Hi!

I would like to build a speaker selector (more a switcher/swapper than a selector) for 7 speakers. The purpose is to basically rotate the configuration of a surround system withouth having to change physically the speakers. Imagine a square with speakers on its edges and vertices that rotates 90 degrees. The selector would be on the speaker wires, not on the preamp stage (there is no other way). All speakers would of course be swapped at the same time.

Here is a basic schematic of this idea with only 3 speakers. I don't know if it would be OK to just switch the relays while playing something loud through them. That is why I thought that using tiny rectifier bridges and a voltage divider made of high value resistors would allow me to see if there is something playing low enough to swap the speakers.

The outputs of the three bridges are tied together because I want to know if there is ANY of the speakers that is playing something loud enough, there is no need to know which speaker is playing something loud.

Let me know if you see any problem with this.
Thank you so much!

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Old 4th August 2015, 09:03 PM   #2
Tinyker is offline Tinyker  Belgium
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The circuit could be simplified if I was certain that switching the speakers while playing something through the amp is safe. I know that speaker protection circuits leave the amp without a load (infinite load to be exact) for a couple of seconds.
The difference with a speaker protection circuit is that here, I would be switching from one speaker to another one (that was probably playing something loud) and I am worried about potential feedback and damage to the amp.

If anybody could point me in the right direction I would really appreciator it.
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Old 4th August 2015, 11:42 PM   #3
Zero D is offline Zero D  United Kingdom
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If you're concerned about no load whilst switching, solder a high wattage 10 Ohm resistor across each of the opened relay terminals, This will present a nice load to the amp/s
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Old 5th August 2015, 12:33 AM   #4
Tinyker is offline Tinyker  Belgium
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Thank you for replying!
Quote:
solder a high wattage 10 Ohm resistor across each of the opened relay terminals
Wouldn't that mean the amp sees a higher load? Resistors with speakers in parallel.. (a bit more than 4 ohms?). Correct me if I am wrong
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Old 5th August 2015, 03:45 AM   #5
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Commercial solid state amplifiers are quite stable with no load and "prefer" it that way. You don't need to fit load resistors of any particular resistance unless you have a another reason to need to keep the amplifiers working continuously. Were you thinking of the warnings against disconnecting speakers from most tube amplifiers? Even if you did fit something low valued like 4R to the NO relay side, there will still be a momentary interval with no load and possibly a click noise anyway.

I can't see there is any problem or need to fit load resistors in your application of simply swapping speakers around though - it's no different to pulling the speaker connector plugs out and "hot swapping" them around manually, where there may be long periods without speakers connected.
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Old 5th August 2015, 03:52 AM   #6
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Just just want to share that I just bought these relays. These are auto relays, 40A, SPDT. And the most important reason I bought this is they use 14 gauge wires for the socket.

I have been looking for switches, can't get this high amp as easy. Not to mention 10 for $24.
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Old 5th August 2015, 11:03 AM   #7
Tinyker is offline Tinyker  Belgium
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Thank you both!
Ian Finch ; so leaving the amp without a load is ok as I suspected but do you think there would be some sort of feedback because of the energy stored in the speaker coil?, since it is energized and swapped within ms.
Alan0354: I am going to use dpdt relays that hold up to 10A, more than enough for my application (130w speakers). I would use 4pdt relays but they are hard to find specially for PCB.
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Old 7th August 2015, 11:42 AM   #8
Tinyker is offline Tinyker  Belgium
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Could anybody else tell me if there would be any feedback to the amp with this setup?
Thanks!
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Old 7th August 2015, 05:00 PM   #9
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I would advise simulating the rectifier setup. I am not sure it'll work with the AGND floating like that.

As far as the speaker switching is concerned, you only need to ensure that at no time will two amplifier channels be shorted out against each other (or to ground).
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Old 7th August 2015, 06:48 PM   #10
Tinyker is offline Tinyker  Belgium
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The ground would be connected to the 12V PSU ground (not on the schematics). I might just go without that if everybody says it is ok to "hot switch" the speakers. I hope relays will hold long enough and keep switching at the same time.
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