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Old 19th April 2012, 12:21 PM   #1
pixpop is offline pixpop  United States
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Default Isolated DC detect circuit?

I want to build an external speaker protection device with its own power supply. I'll most likely use solid state relays to switch the speakers off when DC is detected. This is to protect my speakers against failures in SS amps that I build. Hasn't happened yet, but it's only a matter of time.

I was looking at the DC detector from Rod Elliot for starters.

Loudspeaker Protection and Muting

I had been wanting to power this thing from a wall wart, but this design would then connect the grounds of the two channels together, which would mean no bi-amping, and problems if I accidentally swapped the polarity of one channel.

I could build it with separate power supplies, but that nixes the wall-wart idea, adding a whole lot of complexity to what wold have been a simple project. Or I could just build two separate units, each with its own wall wart.

Does anyone know of an isolated DC detect circuit that would allow me to use a single power supply? Would I cause signal degradation if I put say, a 600 Ohm transformer winding in parallel with my 8 Ohm speakers?
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Old 19th April 2012, 12:29 PM   #2
AndrewT is offline AndrewT  Scotland
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I think Apex showed a speaker mounted protection circuit.
If I remember correctly it was self powered using the excessive audio signal to trigger it.
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Old 19th April 2012, 12:29 PM   #3
pixpop is offline pixpop  United States
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Note: I realize a transformer will not pass DC. If I used a transformer, I would be detecting zero crossings instead of DC.
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