K4700 (speaker DC protection) possible serious design flaw


I’ve been conducting tests with several different ways of breaking fault current from an amplifier to a speaker with a relay. And my tests have concluded that if you don’t wire your relay so that the speaker is connected to ground (through the normally closed contact) when off, an arc will strike and the speaker will receive all fault current.

Here is a video of what happens.

Here is an in-depth article I wrote about it.

The K4700 doesn’t wire the speaker to ground, which is a potentially dangerous situation. In my opinion, it should get an update.

Dear / Madam, I refer to the post by Halgaar who has done extensive tests on the K4700 speaker protection module. He concluded that there is a design fault resulting in arcing accross the relay speaker contacts.
Could I ask the moderator if he/she agrees with this as I am prepared to rewire the relay contacts on my board if necessary.


Maybe the K4700 is not the best solution on the market, but it has been on the market for more than 20 years now, and we have never received a complaint. At this time, we have no plans for a redesign. If we would do a redesign in the future, we will of course consider the remarks this gentleman made.

@Radioscope, it also depends on the power of your amplifier. Do you know how much power it can deliver, or better yet, its supply voltage?

I wonder in what kind of installations the K4700 is mostly used. One can ask; do people install it in amplifiers that already have some form of protection? A lot of amplifiers are current-limited to to protect against DC.

Hello, Many thanks for the replies. Point taken regarding the fact that there have been no complaints in 20 years.
Haalfgar, I’m sure you have done some thorough tests!
My amplifier has a supply voltage of + and - 40v (what velleman refer to as a symmetrical power supply in the kit instructions). It is about 25W per channel, not very powerful but there is enough DC there to damage the speakers under fault conditions; but I expect the K4700 to work correctly.

Most people who attempt to construct the kit I’m sure would be aware as to whether their amplifier has internal protection or not .

So regarding your tests, not sure here if there would be any damaging arcing accross the relay contacts in my case. I’m hoping for the best!
Regards, Radioscope