delay 12v to poweramp

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
a friend has a problem. He has a windowsbased setup in his car and that shitty os makes a few unwanted thumps during startup/boot. we are not sure how to avoid this. we are thinking a ca.20 second delay of amp startup is the easiest fix. how do we do this in an easy and cheap way. we found a relay that probably would work but it costs way to much about 600 nok (100$).
Any ideas?
like this

heres a basic circut of what your asking. It will have delayed turn on and turn off. for capacitor try about 2.2uF to 220uF and you can use a potientoeter to give you the amount of time delay you want. I would be trying for like 20K-250Kohm. There are improvements that can be made if you want.


  • lorne help delay turnon.gif
    lorne help delay turnon.gif
    3.9 KB · Views: 356

Your configuration will not work as you hope, both the transistor and capacitor are not correctly configured for this application.

True, the transistor could be used in either common emmitter (gained voltage) or common collector (unity voltage gain). I would prefer to use a unity gain circuit with the 12V relay because it would make RC calculations simpler, but if you calculate the values making use of transistor gain and minimum base voltage that could be made to work as well. A FET even might be more desirable due to it's high gate impedance that would not interfere as drastically with the RC time constant, but it all depends on the values you select.

Note for the calculations of R and C that RC = T and that is only for one time unit (~63% of full supply voltage applied to cap).

A simple switch like this would work fine IMHO, but remember that if you choose to use the transistor in gained configuration, that the relay will stay on (therefore your amps will stay on) for about the same amount of time after you ground the remote line. If values were calculated for the opposite transistor configuration the turn-off delay would be much shorter than the turn-on delay which might be another desirable feature.

I have modified your posted schematic and attached it below.



  • delay.jpg
    18.7 KB · Views: 344
yes your right about the cap. Mine would turn on right away and turn off after a while. The transistor i think I used correct with + at bottom though generally ground is at the bottom of schematic. Your way does used the base current through the relay so that could be better I guess.
I have often seen where a zener diode is placed across the relay coil reverse biased to protect the transistor. Not sure how important that is or if the calculations are really neccessary considering the cost of a diode.
For a shorter delay turnoff then turn on what I have toyed with is a resistor or resistor+ diodes(for faster change because of ~.7V bias) on the transistor base side of the cap. Seems to work for me.

edit:resistor+ diode in series would be parralleled with the cap.
RE : zagisrule! [] no email recieved... I looked for a design like I described that I made a month or 2 ago but can't find it right now, though it may not be the best design it did work. If there are some principles I missed you can suggest topics or links and dont neccesarily need to explain them.
I'm go with either the 555 timer circuit or the comparator one. You can power the delay circuit itself from the initial remote-on line. If you want an easier solution, I'm sure a local electronics store or online retailer would have a "delayed relay" kit, or at least some surplus time delay relays. something that's suposed to be "on" for __ amount of time before turning off sould also be useful, just reverse NO and NC on the relay!
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.