Source Selector for Car Audio (a - b switch) wiring help

nanl2053

Member
2006-11-07 6:06 pm
I have a Volvo that uses fiber optics from the HU to the amp and is not expandable.

I would like to add a standalone iPhone -> Pre-Amp -> Amp and then have a "junction box" with a switch that will switch the speakers from the factory amp to the second standalone amp.

I have four channels of audio to switch (LR, RR, LF, RF). Is there a switch that's appropriate for this? I think I could use two DPDT switches (one for front speakers, one for rear), but I'm getting confused about how to wire that and if it is ok to use a common ground.

Any suggestions appreciated.

Thanks!
 

Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
You need 1 DPDT relay for each pair of wires going to the speakers. The speakers will connect to the movable contacts of the relay. The two amplifiers will connect to the stationary contacts of the relay.

Be VERY careful when doing this. If you make a mistake and damage the OEM amplifier, it may be VERY expensive to repair.

You can NOT use common grounds for the speakers.

If you don't understand relays, read the 'relays' page of the car audio site (link in sig line below). It's #36 in the directory.
 

Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
The current rating is marginal and only suitable for low power amplifiers.

If you use radio shack relays, you most definitely want to use sockets. When I used them (years ago), they had a high failure rate. There are better relays but they're significantly more expensive. The higher current relays at radio shack would likely be more reliable due to higher contact pressure.