F4 power amplifier

[Bfpca]

Originally Posted by a007udio

Am building the stereo amplifier in dual mono configuration. Is it ok to use speaker protection with common ground, or do i need dual speaker protections as well?

I have used a few protection boards that I got from Ebay. The ones I used had good quality HD relays- Omron, I believe. If you get a stereo speaker protector, it should be using a double pole relay. That way the 2 channels can be completely isolated. The circuitry on the protection board will need to be powered from one channel, meaning that it will be connected to that channel’s PS ground. So, if that breaks your definition of dual mono you need 2 protection boards. You could also add another small PS to power the protection board.
You will only be interrupting the hot output of the amplifier channels and the common side is not interrupted.

[a007udio]

I already have the protection board like this:

UPC1237 30A High Power Stereo Speaker Protection Board Module AC 12V-16V | eBay

It have common ground for both channels.
So my question is, it is ok to wire both power supply grounds from dual mono amplifiers together?

[Bfpca]

You don’t need to run your speaker ground wires through those boards. You only need to run the hot wires through the relays and provide power to the boards. The board looks similar to what I used in my Aleph J but I have omron relays.
I don’t want to pull the amp apart to look, but from memory the ground connections on the terminal strips are just a pass through and the in and out connections are for the + speaker connections. You do not need to connect your amp grounds to the board. Simply insert the protection board relays into the wire from the amp output to the speaker terminal. You need to power the board, which can be done using another transformer for complete isolation or by using the AC from the amp power supply if it is close enough in value. You may need to increase the size of the heatsink on the 7812 if you use higher than 16vac. I used the 20vac in the aleph J and increased the heatsink size so it didn’t run too hot.

[a007udio]

But if i'm right the speaker protection needs ground to work as a DC protector. If there is no ground it will work only as a speaker turn on delay.

[Bfpca]

It’s been a while since I did this work. I should have had a closer look at my documentation for my implementation of the board. I used it as stereo board in an Aleph J and also in 2 monoblock F5t3 amps as mono. Yes that is correct, but you still do not need to run your speaker return to common output current through the board. You can wire it back to the power supply grounds as you indicated in your drawing. If the protection board is truly a common ground you could also connect the 2 ps together directly and run a single wire to the protection board. Have you had any hum issues running the 2 channels completely isolated ?

[ggetzoff]

Of course, the best option (if you don’t a soft start scheme) is to buy the board in the store:

Soft Start & Speaker Turn-On Delay / DC Protector Combo – diyAudio Store

This is the only time I can shamelessly promote a product on the forum.

[a007udio]

I already have the protection board from my old project. And yes, i have some product from diyaudio store and they are great. Only the shipping costs are a bit high to Europe.
So is there any safety issues if i use my old speaker protection board and connect both grounds from dual mono amplifiers to common speaker protection ground?

[chede]

To keep your grounds isolated from one channel to the other, I would use two speaker protection boards, one for each channel.

Of course, each channel's PSU ground then needs its own CL-60 or diode bridge connection to chassis ground / PE. Grounds come together only after their respective CL-60s / diode bridges. That's the way I built my double mono F4.


Regards, Claas

[a007udio]

Yes, i would like to use two protection boards as well, but i have no space for two.
So, if i use only one like above in the picture, will this work?