DC protection Velleman K4701

[Richard9]

I am rebuilding a DIY amp I built many years ago using Elliot P3a power amps.

I realise I need DC protection for the speakers and obviously Rod's P33 project would be a good choice. Problem is no room in the case.

All I need is the DC protection not the soft start or muting. Came across the Velleman K4701 kit that fits in the speaker cabinet and disconnects the amp when DC is present.

It needs no auxillary supply so must get its power from the speaker line - and here is the question. Will it affect sound quality because of this? Anyone any experience of it?

[Original Burnedfingers]

It gets its power supply from the amplifiers power supply. I'm sure there would have to be load dropping resistors from the main supply in order to power this unit. Not the best Velleman kit to choose in my opinion. Velleman has another one with its own 6 volt supply on board and it is a much better piece.

There are those here that will argue that they hear a difference between a signal going thru a relay as opposed to going straight to the speaker. I do not hear any such difference.

While your system is much more primitave than other more expensive sounding systems there is still a need to try to guard against any damage that might rear its ugly head.

[Mooly]

I think it probably uses any DC offset present to power the relay.
Don't you just connect it in series with the speaker. It should have no audible effect in practice, and although it's not the ideal way it has to be better than nothing.
Regards Karl

[theAnonymous1]

The other Velleman kit is the K4700. Below is a guide to improve the circuit.

http://www.anidian.com/audio/deconstruct/k4700.shtml

[Original Burnedfingers]

I think it probably uses any DC offset present to power the relay.

I don't think so... It would take a heap of DC offset to power the relay.

Go with the 4700 and make the modifications.

[nigelwright7557]

The same job can be done with a very basic PIC micro and a relay and a few other components.

I use a PIC12C508, its only 8 pins but it does the job very well.

Mine holds off the realy on power up for 3 seconds.
If the DC level stays above 20 volts or below -20 volts for 500ms it imediately drops the relay.

I use the PIC inputs as comparators using voltage dividers.
I know fro mexperience the threshold for a PIC (5V VCC) input
is 2 volts.

If you want the circuit and software let me know.

Nigel

[theAnonymous1]

Originally posted by burnedfingers
I don't think so... It would take a heap of DC offset to power the relay.

I believe it takes at least 10vdc to trigger the relay with the K4701.

[Original Burnedfingers]

I believe it takes at least 10vdc to trigger the relay with the K4701.

That is why I recommend using the 4700. The 4700 trips with 1VDC. While 1VDC is a little much it is still far better than 10 or 20 volts.

[Richard9]

Thanks for the input guys

I will certainly give this more thought. The 4700 kit with mods may be a better alternative but I will need another box to put it in.

I suppose if the amp has a serious fault it will give full supply rail voltage to the speakers (35V) and even the 4701 kit would prevent this.

[Mooly]

Originally posted by burnedfingers


I don't think so... It would take a heap of DC offset to power the relay.

Go with the 4700 and make the modifications.

Hi, had a look on the Velleman web site, No extra PSU needed, uses the DC offset to operate the relay, that's why I said it was less than ideal, but there you go. I don't know what minimum voltage is needed to trip it
Regards Karl