How-to guide
How to choose the right audio output on an Android head unit
Quick answer
The unit has 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, and a processor with a digital input does not need the analog stage at all.
Before you start
- The specification for your amplifier or processor, so you know which inputs it actually 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 are going optical, because that socket is not reachable once the unit is in the dash.
Step by step
- Know what the unit puts out
Four speaker channels come off the internal amplifier, front and rear, left and right. Separate from those are 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 is also a single analog 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. Running an external amplifier off the speaker outputs puts the signal through one amplifier stage first, and a high to low converter then 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. A gain set by habit for a 2 volt source is too high here, and the first thing that shows up is hiss at idle. Set it against the 4 volt figure and start lower than you think.
- Decide between analog and digital
If your processor has an optical or a coaxial SPDIF input, the signal reaches it without becoming analog 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, the pre-outs are the answer and nothing is lost by using them.
- Know what processing is already in the path
The 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, or the two shape the same signal and you spend the afternoon chasing your own corrections.
- Check the source before you blame the output
The unit plays mp3, m4a, aac, amr, wav, mid, flac and ogg. A file it cannot decode sounds like an output fault when it is not one.
If it does not work
- Hiss at idle on an external amplifier: that is gain, not wiring. Turn it down and check it was set against 4 volts.
- Nothing at a processor on the digital input: check the processor is switched to its digital input before you touch the head unit end.
- Sound on some sources and not others: that is the file or the app, not the output stage.
- A channel 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. The same harness can feed a processor digitally and an amplifier on analog at the same time.
The optical SPDIF socket is on the rear panel, alongside the HDMI output and the antenna connections.
The specification does not state a bit depth or a sample rate for the digital outputs, and it does not say whether they pass audio through untouched. If a build depends on those figures, ask us before you buy.
Still need help?
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