Power on Timed delay?

With both my pre and phono amps i get a turn on rush after powering on. It brings the speaker protection in on the power amp.
I would like to make a timed mute circuit.
I want a circuit that will operate a relay for 20 - 25 seconds after power on. The relay needs to short the signal output to ground, this means signal doesnt go thru the relay.
Apparently a 555 timer chip should do it, but i have no idea of how to sort the circuit.

 

Instead of a timed delay putting another switch in the signal path why not try limiting the surge current on power on.
Use a NTC surge protector thermistor, measure the normal load current and get a suitable thermistor, typically they may have 2 or 3 ohms resistance at 25C, and reduce to 0.02 ish ohms at full rated load. They should have no affect on sound quality and should cure switch on thump, which is what I assume is tripping the speaker protection.
Kev

 

Look up 555 monostable. This should give you what you need. Otherwise in the new year when I return to my notes, I will get the circuit for you.

 

de'Kev, as i said, the signal will not pass thru the relay or any switch what so ever.

Isaac, ive had a quick look and tbh im not confident enough to sort my own values etc.
You offer is much appreciated and would be great.

 

lol

 

about 100k for the resistor and 220uf for the capacitor,however how are you going to get the triger (pin 2) breifly low to start the timing period

 

No idea mate, i realy am not an electronic bod. But the use of the 555 was suggested as being the easiest way to go.

 

Hi,

Have a look here... http://sound.westhost.com/project33.htm

Regards

JC

 

not sure what that is, but doesnt seem to be mute, there is a mute thing there but it puts the signal thru an awful lot of extra components.

 

something likethis is more like it,well apart from the maximum of 5 seconds delay

 

yep, thats the kinda thing. Thanks