DC-protection with delayed turn-on

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For your pleasure, a clever DC-protection with delayed turn-on (anti-thumb).

I immodestly say it's clever as it's not my work but a rip-off of 2 very prominent people which I of course want to acknowledge: Nelson Pass and Douglas Self.

Douglas Self developed the DC-detector; a first order low pass filter cleverly connected to the bases of Q1 and Q2. This arrangement is very fast (100ms if I'm not mistaken) and allows to trigger on differential and absolute DC on output. As it's not extremely sensitive, it allows for about 2V DC before triggering. Handy for balanced ClassA-amps that may take a while before reaching low absolute offsets.

Nelson Pass is the mind behind the delayed turn-on which is formed by mosfets (what else) Q5 and Q6. R6 and C2 form the time constant of the delay. D7 protects against inductive kickback of the relays.

Fred wrote a nice post on high that works in more detail:
http://www.diyaudio.com/forums/showt...265#post175265

With shown values 12V relays can be used (high current relays from Omron). This circuit can be used with a large range of rails (shown values are for +-25V), but higher ones are of course possible with slight adjustments.

I am greatly indebted to Nelson Pass and Douglas Self for sharing their works. In case you mind me using your work I will of course respect that and will not offer people to get boards at cost.

As my amp is getting close to primetime and I will order boards for myself soon, folks interested in boads just feel free mail me. Beware that no prototype was yet build, so you know you have to test it first

Have fun, Hannes

PS: sorry had to cut the schematic to be able to post it here.

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Geez, where did the 2nd part go?