MattW

I'm going to be installing my 'carputer' (heh, still can't say that word without a chuckle!) in my dad's Accord for now, until I get my own car, so it brings up a lot of issues. One is, I don't want to replace the head unit (money issues, heh), and I'd like to just use a 4-channel amp instead. But, I'm sure my dad would like to keep using the current radio, so I want to have both connected up to the amp. I'm thinking this could cause problems if both the amp and the radio were outputting power at the same time, or something. So, I should probably use a switch, right? What about relays? I'm worried that electromechanical relays might add some noise to the signal path, but I don't know. I suppose that if this is a problem, I could just use semiconductor relays. What do all of you think?

Squeezer

why not just use an FM modulator for the computer and then use the FM tuner on the head unit. Or if its a tape deck use the stereo to tape adaptor.

__________________
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2000 Honda S2000

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MattW

That's what I'll probably do at first, but the sound that way will be quite a bit inferior.

Aaron Cake

Solid state relays will not work for this application. Best bet would be to buy or build a mixer of some type, or just connect electromechanical relays with a switch. Going relays is certainly the cheapest solution, and shouldn't cause noise problems as long as they are sealed from the environment.

__________________
Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
"If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."

Dustin Haug

If you don't want to use a modulator or adapter, do like Aaron said and use mechanical relays, get one DPDT for each speaker, wire the coils in parallel and you should be good to go. If your amp is very big you should get decent sized relays or you could melt them.

Aaron Cake

I think he's talking about inputting to the amp, not outputting from it. So small relays should do fine.

__________________
Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
"If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."

MattW

Outputting, actually. Well, cool, so I'll go grab some relays some time and hook it up to my home stereo just to make sure there isn't any/too much noise.

Aaron Cake

Huh? By your post above, it sounds like you want to input two different signals into the amp, switching between them (the computer, and the radio). What exactly are you trying to do here?

__________________
Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
"If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."

cruzc_99

I think that he is trying to input two signals in to the amp at the same time too. And if thats the case it shouldn't be a problem. I mean thats the reason amps have auxillarry inputs right. even if you did happen to play the radio at the same time you played the carputer it wouldn't cause any problem, it would just sound like sh**

At least that is what I am assuming because that is how mine will be hooked up in a few weeks.

Let us know how it works

Dustin Haug

My understanding was that he wanted to be able to switch the inputs to his speakers from the factory radio to his amplifier/mp3 player. He could do this with DPDT relays. Matt if this isn't what you wanted to do post again and clarify.

MattW

Sorry about the confusion. I'm going to be connecting an amp and a car radio to the same speakers, so that I can use the car computer with the amp and my dad can keep using the crappy old car stereo.

Dustin Haug

Then what I'd do is get DPDT relays (one per speaker) and wire them up like this.

NO1 -- amp speaker(+)
NC1 -- radio speaker (+)
NO2 -- amp speaker (-)
NC2 -- radio speaker (-)
Com1 -- speaker (+)
Com2 -- speaker (-)

Do this for each of the speakers and be consistent with your wiring as far as if the amp or radio is on the NC or NO terminals or you could have a mess. Once you have all of this done, wire the coils of each of the relays together and run one side to ground, run the other side to one terminal of a switch and the other side of the switch to 12V. Then when you have the switch off the radio will be connected to the speakers, when the switch is on the amp will be connected to the speakers. Enjoy!!