Speaker protection pcb design

[davidsrsb]

As I am bored, I have decided to do a quick charity-ware speaker protection pcb, as Velleman seem to have stopped making their module.
I was reading an old Doug Self article in Wireless World and the discussion about the SSR design in this topic.

So I am planning to try to do it digitally, as a Shield for an Arduino Uno
First thoughts:
Use back to back Si4090DY mosfets 100 V, 20 A,10 mOhm in a hand solderable SOIC-8 package
Switch them using the Toshiba TLP3906DP - hand solderable

Use two channels of ADC to sense speaker DC, Attenuate, low pass filter and level shift by pullup to 2.5V
AC power detection
Fault LEDs to indicate which channel has a DC fault
These parts can be through hole to make hand soldering easier

The Mosfets and driver will be cheaper than a genuine relay able to handle the power

Your thoughts please.

 

[nobeone]

I think offering a PCB to others that they can use in place of the Velleman is a great DIY contribution.

Not sure why you would want to make that a Shield for an Arduino Uno though. Just my 2p.

 

[Vinny]

Design as a one channel board or a two channel board that can easily be separated/cut into two singles.

 

[chiily]

One thing I do like about the Velleman boards in the built in PSU, means I don't have to knock up another PSU (transformer/diodes/caps) on a separate board. I would prefer that the board has a regulator so I can wire it up to the output of the amp's PSU, rather than a separate PSU board.

 

[davidsrsb]

...Not sure why you would want to make that a Shield for an Arduino Uno though. Just my 2p.

Because it is easy to do very precise timing in the digital world. Allow, say, one and only one missing cycle before tripping

The article that inspired me was "Self on Muting Relays" in WW July 1999.
He had some fairly complex analog circuitry to get the timings and he ran from +/- 55V, so the design would have to be tweaked for other supply rails

 

[davidsrsb]

One thing I do like about the Velleman boards in the built in PSU, means I don't have to knock up another PSU (transformer/diodes/caps) on a separate board. I would prefer that the board has a regulator so I can wire it up to the output of the amp's PSU, rather than a separate PSU board.

I think a small off board transformer and a bridge and bulk capacitor will fit. The Uno has a 5V regulator

 

[S-Man]

uPC1237 works very well IME. As a uC numpty I'd stick with analogue.
+1 for individual channels. +1 for run the board(s) from the amp supply rails.

Good project!

 

[davidsrsb]

It's a challenge. The uPC1237 is actually fairly hard for an amateur to buy from reliable suppliers.

Adding 68V 600W bidirectional diodes to catch the breaking transients

 

[Vinny]

In terms of signal/sound quality, why would you go for SSR rather than a mechanical relay? Fair enough, you'd need to select, and occasionally change-out, a good quality mechanical relay and not so with an SSR. Selection of SSR too?

Surely the SSR cannot help but change the signal?

Chinese units will run from a wide range of supply voltage, AC or DC.

 

[Shadders]

Surely the SSR cannot help but change the signal?

Hi,
I am intrigued by your statement. Surely a mechanical relays can change the signal too ???

Regards,
Shadders.

 

[davidsrsb]

A pair of mosfets driven by a floating voltage source is actually a very good analog switch. The body diodes don't even come close to turning on at any point.
We are talking about 20 mOhm in series with the speaker positive, good luck to getting a power relay anywhere near that after a few weeks of breaking Amp level currents when the power is switched off.

Checking around, I don't see any normal sources of the uPC1237, maybe that is why Velleman have dropped what must have been one of their most popular kits.

 

[Vinny]

Point taken, but who switches a power amp off when there is signal present?

 

[bravem01]

Use a Nano instead of a uno, same code but smaller footprint and very cheap

 

[davidsrsb]

Anyone just listening to the radio perhaps

 

[davidsrsb]

I probably need the space, as I am trying to do a hobbyist friendly soldering job.
Unos are very cheap in KL, less than £5.
Nanos are rarer

 

[James Evans]

The K4700 looks to still be in production and widely available?

http://www.velleman.co.uk/contents/en-uk/p240.html

 

[cj66]

There was another kit sold by Jaycar, now discontinued. It was a Silicon Chip design and works well in my DIY Aclass power amp ( also a SC design but heavily modified by Sandyk and others on DIYAudio etc. forums).

I digress, I might still have the printed instructions which shows the circuit diagram and graphic of the printed board, along with the BOM.
Any use?

 

[Arkless Electronics]

It did seem strange that Vellemen would stop making what surely must be their best selling module...

 

[Mike Hanson]

It did seem strange that Vellemen would stop making what surely must be their best selling module...

Perhaps in Europe, but you can't get the North American version any longer, and they no longer supply the necessary transformers to replace them. They're not even listed on www.vellemanstore.com, which I believe is their N.A. store.

 

[Arkless Electronics]

Perhaps in Europe, but you can't get the North American version any longer, and they no longer supply the necessary transformers to replace them. They're not even listed on www.vellemanstore.com, which I believe is their N.A. store.

Hmmm they are still there on the .en European site as well as the ,co.uk site and no mention of and of life or anything... Maybe just a N America thing?