Speaker Protection/Mute Box

I made a couple of these a few years ago.  This one uses Speakon sockets and is the better of the two.  Inside is an ESP Project 33 PCB controlling a couple of high-current relays and a 15V power supply to run it.  It has a 2mm tip LED in the front panel to indicate that power is on and that the relays are in the “speakers-connected” position.

It is for connection between the speaker outputs of a solid state power amplifier and the speakers.  If the power amp has a switched mains output, it can be used to power this box so you don’t have to manually activate it.  Otherwise you can leave the power amp front switch on and plug this into the same power strip and switch them both on and off from there.  Since the photos were taken I changed the wiring to exploit the “loss-os-AC” detector so that muting is instantaneous at shut down.  This is good as it mutes before any amplifier shut-down thump can get through to the speakers.  It also mutes the speakers if amplifier fault DC is detected.

2 thoughts on “Speaker Protection/Mute Box

  1. Hello…

    I plan to build a amplifier with esp101 and esp33 boards.
    Can you tell me the type and manufacturer relay you have used for the speaker protection ?

    thanks in advance

  2. It doesn’t matter too much since they’re sacrificial parts (the contacts will weld closed if the ampliier goes DC). I just used Omron or a similar brand with the highest 12Vdc coil resistance that I could find at the time and a 15A contact rating. Try Element14 or RS. the model numbers seem to change all the time. Use SPDT for a single channel or DPDT for dual. There’s someone at the ESP forum that uses fancy dual contact/progressive relays, but I see little point as they’re gonna fry anyway.

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