K&K Audio / Lundahl Transformers

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RE: Start up and shut down noise

Posted by KevinC on August 2, 2016 at 16:26:35:
Hello again!

The time delay kit will pull in or break relay contacts after an N second delay, where N is adjustable by means of changing a resistor value, so it can very well be used to mute the amplifier output until power up is complete.

On the turn-off end, the relay will open/close (depending on which set of contacts you wire the load to) upon power off, but not instantaneously, because the timer power supply capacitance is not zero. It can certainly be reduced from the value supplied with the kit (1000uF) to shorten the time to "release", but it still won't be fast. I have used another method to provide suppression of SE preamp turn-off bump, which is to use a 24VAC relay to short the output when power is removed. AC relays don't seem to be available in voltages less than 24V, although you can get 115 and 230VAC relays, too. With AC power there is no power supply capacitance to delay action.