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Old 12th August 2005, 02:20 PM   #1
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Join Date: Aug 2005
Default build rca switch for preamp signals

Hello.

I just purchased a Sirius Satellite Radio unit for use in my car. The FM broadcast works through the radio, but I'm sure it would sound a lot better if I go directly through my external amp. My head unit doesn't have an aux in, so I was wondering if anybody could point me in the direction on where to get parts to build a switch to switch the input to my amp back & forth between the RCA outs on my head unit & the RCA out on the radio.

I'd rather make a small, custom switch I could hide in my ashtray or somewhere else less conspicuous than one of those bigger, RCA switch boxes you can get at Target. Car is a Mustang so there isn't much room for hiding things.

Thanks,
Stoney
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Old 12th August 2005, 11:03 PM   #2
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Join Date: Nov 2003
Location: Louisiana
A couple of notes on RCA switching...

You need to switch grounds as well as signals. If you tie all of the grounds together and the Sirius radio is grounded to the vehicle, you may get engine noise. If you use a toggle switch, you'll need at least a 3 pole double-throw switch. 2 poles will be for audio, one for the shield grounds (left and right shields can be tied together for each source - assuming that your head unit doesn't have balanced RCA outputs).

It would be good to switch the amplifiers off when switching between sources. You could do it if you could find a switch with 4 poles but they are hard to find and some amplifiers won't like being switched on/off/on as quickly as the toggle switch will do it.

Typically, the output signal is AC coupled (a cap blocks the DC from the audio circuit). These capacitors will leak DC if left open. When you switch between components, there may be a pop. To help prevent this, you can connect a 100K ohm resistor across each of the RCA outputs of each device (one end of the resistor connected to the center conductor and the other end of the resistor connected to the shield of that channel). This will prevent the build-up of DC on the signal line and there should be no pop when switching.

If your Sirius unit is feeding the antenna input of your head unit and the head unit is driving the amp, the Sirius signal is being amplified.

If the Sirius radio doesn't have a wired RF connection, you could use an RF modulator but beware that some sound fine and some are not so good. Before buying one, try to find some reviews or try to find a forum where they have more experience with them.

If you go directly to your amplifier and your Sirius Radio has no tone controls (bass, treble, loudness), you will lose the ability to make those adjustments.
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