I've designed a simple speaker protection board using the UPC1237 (Unisonic Taiwan is the manufacturer, originally uPC1237 from NEC) that uses mosfets rather than a relay to switch the speaker. The circuit operates from 25V to 75V with some resistor changes (detailed in the write-up), features power up/down muting, DC offset protection and an input to trip the protection on overcurrent (you will need to arrange your own short circuit detection - the board just takes an input for this as a trigger).
There's a presentation with the circuit, BOM and if you want a board, you can buy one off the website.
https://hifisonix.com/projects/hifisonix-speaker-protection-board/
Happy soldering
See here for where to connect the AC detect input in split power supplies: https://www.diyaudio.com/community/threads/speaker-protection-board.377896/post-7283100
There's a presentation with the circuit, BOM and if you want a board, you can buy one off the website.
https://hifisonix.com/projects/hifisonix-speaker-protection-board/
Happy soldering
See here for where to connect the AC detect input in split power supplies: https://www.diyaudio.com/community/threads/speaker-protection-board.377896/post-7283100
Last edited:
The UPC1237 is available - mainly from 2nd tier distributors. It makes for a very compact board that would otherwise not be possible with discretes.
Here in the UK you can get them from Cricklewood Electronics in London - they do mail order and have a website.
Integrated Circuits Base Numbers Beginning From TE to Z | Cricklewood Electronics
I'll try to find an equivalent supplier in the US and post it up.
Here in the UK you can get them from Cricklewood Electronics in London - they do mail order and have a website.
Integrated Circuits Base Numbers Beginning From TE to Z | Cricklewood Electronics
I'll try to find an equivalent supplier in the US and post it up.
How well does this work when the P-P voltage of the audio signal is lower than the turn-on voltage of the MOSFETs?
As in listening at very quiet volume levels.
Perhaps an isolated floating DC source is needed between the optical coupler and the MOSFETs? This would assure the MOSFETs are fully kept in the “on” state even when the audio signal amplitude is <1V. The required current is very low since it is driving only the MOSFET gates.
-EB
As in listening at very quiet volume levels.
Perhaps an isolated floating DC source is needed between the optical coupler and the MOSFETs? This would assure the MOSFETs are fully kept in the “on” state even when the audio signal amplitude is <1V. The required current is very low since it is driving only the MOSFET gates.
-EB
photovoltaic
The optocoupler is photovoltaic so no gate voltage source is needed. The FETs have reverse body diodes but they have milli-Ohm on resistance so it is unlikely the drop across them will reach the diode forward voltage.
Years ago, I added a small capacitor(s) to the speaker protection circuit of an Adcom amp because the roller rink it was used in had a grounding problem that make it prone to high frequency oscillations. This disconnected the speaker if the amp produces a high power ~10KHz+ voltage, fast enough to prevent this from killing the amp. It never failed again, although I also cross-coupled it and un-bridged the output. I recommend adding ~ 1nF caps (plus a small resistance ~500 Ohms) bypassing the DC filter so that such a voltage is rectified and trips the relay.
The optocoupler is photovoltaic so no gate voltage source is needed. The FETs have reverse body diodes but they have milli-Ohm on resistance so it is unlikely the drop across them will reach the diode forward voltage.
Years ago, I added a small capacitor(s) to the speaker protection circuit of an Adcom amp because the roller rink it was used in had a grounding problem that make it prone to high frequency oscillations. This disconnected the speaker if the amp produces a high power ~10KHz+ voltage, fast enough to prevent this from killing the amp. It never failed again, although I also cross-coupled it and un-bridged the output. I recommend adding ~ 1nF caps (plus a small resistance ~500 Ohms) bypassing the DC filter so that such a voltage is rectified and trips the relay.
Last edited:
Thanks Andrew but buying from London isn't possible after Brexit.
Buying from ebay can't be sure what you will receive.Looking at the ebay i see many-many unbranded.That's why i say hard to find part.
Last edited:
Buying from ebay can't be sure what you will receive.Looking at the ebay i see many-many unbranded.That's why i say hard to find part.
Hi Thimios,
You can always get the uPC1237 from France (still in EU for the moment
) here.That's where I get them from.
I am not affiliated with that shop, just a happy customer.
Cheers,
Jacques
Hi Thimios,
You can always get the uPC1237 from France (still in EU for the moment
That's where I get them from.
I am not affiliated with that shop, just a happy customer.
Cheers,
Jacques
Thanks dear!
I looked to this supplier but i can't see what's brand.Posted pdf is from Nec.
Last edited:
Thanks dear!
I looked to this supplier but i can't see what's brand.Posted pdf is from Nec.
I'll take a picture tonight and post it.