Hey guys. I thought I'd ask this question over here, most of the car audio related forums are quite a bit less experienced than us pro audio geeks when it comes to electronic design.
Being a sometime circuit builder and tweaker (basically building projects, no design!), I got to thinking about the audio system in my new Toyota Corolla S. (this car is awesome by the way, and I sold an Audi A4 to get it)....
I am putting my old audio system from the Audi into the Crayola, but I want to keep the factory head unit. For a lot of reasons, but security is the primary reason. And new radios are hideously ugly. My friend who runs an install shop showed me an attenuator box to bring the speaker-amplified head-unit signal down to line level. Needless to say, this made my stomach turn.
So I want to add line-level outputs to the factory head by intercepting the signal from the preamp section before it hits the power amp inside the head unit. The power amp is likely at the rear, as I think there'll be some heatsinks back there for the FET amps or whatever.
So where should I grab this signal? Will there likely be coupling caps and a resistor before the amplifier section that'll be pretty obvious? Can I just trace ground somewhere or grab it from the chassis? I was going to put a 50-100R resistor on the where I do the interception to alleviate possible oscillation.
Do I need to keep the coupling cap in line before my line-level cable going out of the unit?
Should I remove the coupling cap from the amp side and prevent the signal from even hitting the internal amp section? Should I upgrade or further bypass this cap if I do need to keep it inline?
Should I isolate even further with a transformer or something?
The destination device is a little EQ/crossover about 10" away, so cable driving ability is not needed. I could make it 6" if necessary.
And no, the radio does not have line outputs or a factory external amp (so I am told by the pros, anyways).
Thanks for any suggestions. You guys rock.
Chris
Being a sometime circuit builder and tweaker (basically building projects, no design!), I got to thinking about the audio system in my new Toyota Corolla S. (this car is awesome by the way, and I sold an Audi A4 to get it)....
I am putting my old audio system from the Audi into the Crayola, but I want to keep the factory head unit. For a lot of reasons, but security is the primary reason. And new radios are hideously ugly. My friend who runs an install shop showed me an attenuator box to bring the speaker-amplified head-unit signal down to line level. Needless to say, this made my stomach turn.
So I want to add line-level outputs to the factory head by intercepting the signal from the preamp section before it hits the power amp inside the head unit. The power amp is likely at the rear, as I think there'll be some heatsinks back there for the FET amps or whatever.
So where should I grab this signal? Will there likely be coupling caps and a resistor before the amplifier section that'll be pretty obvious? Can I just trace ground somewhere or grab it from the chassis? I was going to put a 50-100R resistor on the where I do the interception to alleviate possible oscillation.
Do I need to keep the coupling cap in line before my line-level cable going out of the unit?
Should I remove the coupling cap from the amp side and prevent the signal from even hitting the internal amp section? Should I upgrade or further bypass this cap if I do need to keep it inline?
Should I isolate even further with a transformer or something?
The destination device is a little EQ/crossover about 10" away, so cable driving ability is not needed. I could make it 6" if necessary.
And no, the radio does not have line outputs or a factory external amp (so I am told by the pros, anyways).
Thanks for any suggestions. You guys rock.
Chris
