Solid-state turn on relay.
 

Well, it's not really a relay, but you can use this circuit in place of a relay
on turn-on circuits. This is not new stuff. Clark and Navone covered this topic
20 years ago. I've had a few inquiries, 'cause I mouthed off about how this works
better than an electromechanical relay. (no clicks or pops) So, here's the TOP SECRET STUFF us old guys don't like to share.

http://http://s790.photobucket.com/a...thetubedoctor/

Couldn't get the link to work

Sticky!!

Oh, a transistor? Pretty much does the same job as a relay :P

Good to know... how many pennies does it cost to build?

Locally, (Hong Kong) a buck for the TIP 120, two bits for a couple of resistors and 5 minutes of your time. And NO coil transients!

So they are good in place of a SPST relay for 3.5amps? I know of a few in my car that could use the swap.

I can't remember the last time I used an electromechanical relay for an amp/processor remote turn-on circuit. I habitually buy a handful of the necessary parts every time I'm at the supply shop. If I remember, I'll also pick up a couple of little heat-sink tabs, then I'm
safe for 5A with a TIP 120.

BTW, you'd LOVE the street where the supply shop is located. 3 city blocks of street market stalls, ground floor shops, and bunches of 1st & 2nd floor walk-ups, all of them selling electronics stuff of every description.

I built a latching relay (a momentary pulse to ground will turn a constant 12v on/off) that uses my O/D button on my gear shifter to turn on/off my sub amp... its constructed of 3 SPDT relays, 1 SPST and a couple diodes... it does however induct the faintest bit of noise (and plays out my tweeters) when it is energized...

I'm sure we would enjoy having access to all those electronic components