sundance-communications.com Forums Member Forums Phone Booth Aux Input for my Car, some design q's?

So I'm putting an auxiliary input into my car using a 3.5mm stereo jack with tip switch, two solid-state relays, and 4 RCA jacks all soldered up on a breadboard. Planning to have the pre-amp output from the radio going to the NC side of the relays, the 3.5MM jack go to the NO side of the relays, and the common of the relays to to the amp loop wiring. The tip-switch from the 3.5mm jack will be used to complete the control circuit and trigger the relays.

It sounds simple enough but I have a question concerning relay activation and the external jack. Should I put some kind of cap/res combo at certain points of this thing to prevent sending a loud popping through the stereo amps? I'm not looking for active electronics and all that but if it's something simple that can be done and it prevents me from blowing a speaker or amp then I'm all for it.

Thanks for the help guys.

why not just buy an aux input adapter?

https://www.crutchfield.com/app/pro...earch=auxiliary+input+adapters&ssi=0

I used one of these on my jetta. It connected to the factory stereo's cd changer port. The install was real simple and its been in use for years.

Kumba, I don't know if this helps (and you probably know this already), but when I read your post it reminded me of the input design on older audio equipment: If an amp or pre-amp had more that one input, the switch to select the input was usually a rotary-type switch with a shorting or "make-before-break" contact design. I'm not sure how this relates to the circuit you are building with solid state relays, but it might be food for thought.

I have a buddy who is heavily into building audio gear, unfortunately he is down south right now. As soon as he returns I will put your question to him, but by then you will probably be done..

Jim
**************************************************
Speaking from a secure undisclosed location.

An RC network designed for the protection of the contacts from arcing should also take care of your concerns.

It sounds simple enough but I have a question concerning relay activation and the external jack. Should I put some kind of cap/res combo at certain points of this thing to prevent sending a loud popping through the stereo amps?

I wouldn't even worry about it until you build it and actually find that it is a problem. Normally standard practice is to put a general purpose diode (like a 1N4004) across all relay coils, observing polarity of course. But that's about it.

The "make before break" is a good idea but you won't find that in a relay.

Oh, I'm also confused by what you mean by a "solid state relay". If it's anything other than a coil and actual contacts you can't use it here.

-Hal

Superb advice re the diode, Hal. However, it seems like the appropriate SSR might work for him in lieu of that technique. There's a general article about solid-state relays on Wikipedia or better yet, take a look at the specs of this SIL-rated SPST solid-state relay (say THAT three times fast) from Crydom.

Yeah, my thought behind using a solid state relay was to hopefully try and eliminate popping and hum when they are activated.

Sounds like i'll just take Hal's approach and wire it up and see what happens. Worse case scenario I guess I get a couple nasty pops before I figure out I need to do something. Since it's on the pre-amp side I am pretty sure it's not going to blow out the headphone jack in my phone or anything like that.

I wouldn't want anything that uses a triac or other non-linear switching device in an audio circuit. Maybe I'm behind the times but as far as I'm concerned they should be limited to switching simple DC or AC voltages.

-Hal