Stock Headunit + Carpc working Simultaneously

**fire** · 03-10-2007, 04:30 AM

Hi everyone...
i've got a capc in my car and have had so for the past 2 years...
works perfectly... its a PC in the boot connected directly to amps and to the speakers...
im now selling the car and stripping it out... and am designing my next carpc..

I missed having a headunit when the computer had problems, or just wanting to listen to AM. ... even playing a CD when a mate came in the car was hard...
so ive decided to leave the stock headunit and add in a screen+carpc as well..

i want to get decent sound from both headunit (no aux in) and carpc.. so i was thinking:

Stock headunit --> stock amp --> pioneer PRO speakers via stock Speaker Wires
and in addition to this:....
Carpc --> Optical / digital converter --> good amp --> pioneer PRO speakers via THICK speaker wires

now... as you an see thats two seperate systems that get connected at the speakers..... as far as i know.. this wont work (as one amp will be feeding signals into the output of the other amp)..

so my question is how can i do this???
im guessing its not as easy as diodes (which probably loose signal quality if they did work anyway)

**ralphyboy** · 03-10-2007, 07:57 AM

The best and easiest way to get what you are asking about is to run a line level converter off the stock head unit and into the amp using y connections, it would look like this using your drawing.

Stock head unit->Line level converter->
Carpc --> Optical / digital converter --> good amp --> pioneer PRO speakers via THICK speaker wires

It will play both if you leave both on but it won't be bad for the system as long as both are not turned all of the way up, just annoying. In the same manner you could go line level into the computer and route it that way too, not the way I would do it since the head unit is available nearly instantly and it takes time for the car pc to boot, but you could is more the point. I hope this helps some.

**fire** · 03-10-2007, 07:02 PM

thanks for the reply... .. well that sorts out the issue..
and as a benifit i can remove the stock amp..

however in the y join that i will have before the new amp on the RCA side of things...... would that not drop signal quality at all?
is there any way to "switch" it??..

**scott_fx** · 03-10-2007, 07:53 PM

do not hook both up like that. you need a mixer or switcher. a mixer will allow two sources to be played simultaneously safely (if you want to here gps nav on the computer while listening to the stock head unit) while a switcher will safely switch between two devices.

with usb cd/dvd drives and the new am/fm and hd radio options out there your old problems are a thing of the past. i'd say do it right the first time and don't mess around with these types of patches. if you have a different reason for keeping the stock head unit..then that's another thing, but what you have described doesen't seem like a valid reason not to drop the head unit.

**ralphyboy** · 03-11-2007, 12:04 PM

If the vehicle is amplified via an external amp stock you would still need the stock amp. I do not know the particulars of your systems voltages but most amps today should be able handle even full volume from both sources with something that does not have a line driver built in, I imagine Scott would know better than myself but it seems to me at wost it would cause feedback but no damage at all, I might be missing something simple though. It would be easy to even build a simple switch yourself if that is what you wanted. RCA cables are not complicated at all, they are just 2 wires 1 run inside of the other. You could hook up a 3 position switch to have only 1 or none of the RCA's not allowing power through. It would cost like 5 bucks at radio shack, I'm sure there are commercial ones available too.

**scott_fx** · 03-11-2007, 08:55 PM

a simple 4 pole relay would work as a switching defice on a stereo set of rca's

**fire** · 03-11-2007, 11:43 PM

as for getting rid of the head unit.. i havent had one in the car for the past 2 years.. and Radio is just too hard... its crap quality... not as easy to use during the day.. and if for some reason the carpc didnt work... i'd have nothing in the car.... i have a slot loading dvd burner up in the dash.. and that was a pain to play CD's.. and when it spins, its too loud.

ahh yep.. i like that idea with relays...
i might create a little box with 8 RCA inputs, and 4 RCA outputs...
that would sort it out...

i understand that i can get a single relay.. or 2 relays with many contacts.. but just for simplicity while drawing.. i just seperated them all.

can i join the grounds on any of them to make it easier????....
do i need any specific relays (so i dont loose quality?)
i will probably use 2 relays..so that i can have fronts on radio (head unit) and rears on Carpc... GPS..