Velleman K4700 Schematics
Several people asked me to put the Velleman K4700 protection-circuit schematics on my blog. So here it comes.
This circuit is indeed the ideal replacement for the (lousy) protection-circuit in the original Quad 405. It does not only eliminate completely all power-on or -of "Plops" it also gives the best protection for the speakers against DC-current. The 405 has the nasty habit to put -50 Volt DC on the speaker-outputs if one of the power-transistors is broken...
I build this protection-circuit in most 405's and 405-2's I upgrade.
There is no use at all trying to "reconstruct" the Velleman protection-circuit as it is sold for +/- 20 Euro by Velleman with excellent components. See www.velleman.be