turn on delay - imediate shut down

[sunrise]

hi guys,
i need some circuit that will delay turning on my preamplifier output for 10 or 15 sec. but when i power the pre off it needs to power it under 0,5 sec or maybe little bit more but definetelly under 1 second.
So - when power of - imediate shut down and when
power on - delay of some seconds (lets say 10-15 sec)....
thanks for replies
sunny

[mazurek]

I've been meaning to post my preamp power supply for a while. It has a circuit that waits until power is 2 volts above regulator dropout, and turns off instantly. To test it I have turned on and off the hard power, and no pops. I can post it if you want.

Its basically just two transistors, one for ac detect, and one for dc detect.

[sunrise]

Hi, Mazurek,
i need some circuit that will detect that i am turning of the preamp and than to disconnect the output of the preamp....I am using +/- 15V for power supply for the preamplifier.....Also i need some delay when i power up the circuit in order not to damage output amp (so that after few seconds when the preamp is turned on it connects the output of the preamp to the output connectors).
If Your circuit can do that i would be happy and honoured to build it and use it....thanks for the kind reply
sunny

[mazurek]

heres a picture of my switch, values are set up for a 12 volt supply, I don't think its critical to change anything except the zener. My switch controls relays which short the crossover output, and it is noise free.

[ifrythings]

Sorry mazurek , I was borded and decided to neeten things up

[sunrise]

Thanks Mazurek,
also thanks to ifrythings....nice drawing

The problem here is that i don't have turn on delay too.......this circuit is only for turning off....
how can i put also power on delay inside this or some other circuit (maybe there is some other circuit that has it all - don't know)

thanks and regards
sunny

[ifrythings]

That cicuit has turn-on delay, it delays the relay until the power supply has hit a limit, which prevents the good old thumpsand bumps your speaker does.

The bigger the cap is in that supply, the longer it takes for it to turn-on, but then your turn-off time goes to crap.

[jaycee]

If you want instant turn off all you have to do is make sure that the AC detect will shut off the transistor as soon as more than 3-4 cycles of AC are missing. The power supply caps will hold up for longer than that. There's no need to do any kind of voltage drop detection from the regulator output.

[sunrise]

ifrythings.....oh boy - i did not see that one... so in other words i receive here short turn on delay and fast turn of .....this seems to be what i need
sunny

[mazurek]

Thanks for cleaning it up ifrythings, I was a little sloppy because I thought it would be clearer not to duplicate the whole psu schematic.

jaycee, yes, only the ac detect is needed for turn off.

The DC detect does do what you want, as explained buy others, the turn on delay is caused by the main psu caps charging. Once they charge past the regulator dropout voltage, there is no more risk of turn on pop, and it has been delayed enough.