How-to Guide
How to Choose the Right Audio Output on an Android Head Unit
Quick answer
Your unit puts out four speaker channels from its internal amplifier, 5.1 channel RCA pre-outs at 4 volts RMS, and two digital outputs. Which one you use depends on what your amplifier or processor will take.
What this gives you
The output you pick sets the ceiling on everything after it. Feeding an amplifier off the speaker wires when there are 4 volt pre-outs on the same harness costs you noise floor for nothing. If your processor has a digital input, you don't need the analogue stage at all.
Before you start
- The specification for your amplifier or processor, so you know which inputs it has.
- Harness A and Harness C, both supplied. The pre-outs and the coaxial digital output are on those two.
- Access to the rear panel if you're going optical, because you can't reach that socket once the unit's in the dash.
Step by step
- Know what your unit puts out
You get four speaker channels off the internal amplifier: front and rear, left and right. Separate from those, you've got the 5.1 channel RCA pre-outs, covering front, rear, centre and subwoofer. Then there are two digital outputs, one optical and one coaxial. There's also a single analogue AUX input, which runs at 300 to 500 millivolts RMS.
- Use the pre-outs rather than the speaker wires
The RCA pre-outs are a line level signal taken before the internal amplifier. If you run an external amplifier off the speaker outputs, your signal goes through one amplifier stage first, then a high to low converter has to undo it.
- Set your gains against 4 volts, not 2
The pre-outs run at 4 volts RMS across all 5.1 channels. If you set a gain by habit for a 2 volt source, it's too high here, and the first thing you'll hear is hiss at idle. Set it against the 4 volt figure and start lower than you think.
- Decide between analogue and digital
If your processor has an optical or a coaxial SPDIF input, your signal reaches it without becoming analogue on the way, which matters most on a long run down the transmission tunnel to a rear mounted processor. If it only has RCA inputs, use the pre-outs, you lose nothing by doing it.
- Know what processing is already in the path
Your unit carries a 48 band equaliser and DTS processing across 5.1 channels, on an SI47925. Set that flat before you tune an external processor. Otherwise the two shape the same signal and you'll spend the afternoon chasing your own corrections.
- Check the source before you blame the output
Your unit plays mp3, m4a, aac, amr, wav, mid, flac and ogg. If you feed it a file it can't decode, that sounds like an output fault when it isn't one.
If it does not work
- If you get hiss at idle on an external amplifier, that's gain, not wiring. Turn it down and check it was set against 4 volts.
- If you get nothing at your processor on the digital input, check the processor is switched to its digital input before you touch the head unit end.
- If you get sound on some sources and not others, that's the file or the app, not the output stage.
- If a channel's missing on the pre-outs, check the RCA convention on the harness: white is left and red is right.
Worth knowing
C6 on Harness C is the coaxial digital output, and it sits next to the centre channel on C2 and the rear pre-outs on C3 and C4. You can feed a processor digitally and an amplifier on analogue off the same harness at the same time.
You'll find the optical SPDIF socket on the rear panel, alongside the HDMI output and the antenna connections.
The specification doesn't give you a bit depth or a sample rate for the digital outputs, and it doesn't say whether they pass audio through untouched. If your build depends on those figures, ask us before you buy.
Still need help?
Tell us your vehicle and what you're seeing on screen, and we'll point you to the right step.