Briefly, I bought a new-to-me motorcycle which has an AM/FM/CD stereo with an aux input jack, 3.5mm stereo cable sized. So as to have a collection of music at hand, without needing to change CDs all the time, I bought a small MP3 player and stuffed it with music. Plugged it into the aux input and it works just fine, except that the output volume is a bit too low. The bike's stereo has plenty of volume to be heard over the engine noise with FM and CDs, but the MP3 player doesn't deliver the output, apparently.
I have a tiny headphone amp that I use on airliners with headphones. It is a Fiio brand, made in China, although they don't list the specific model I have on their website (perhaps it's a knockoff version). The website does have a similar unit, and the specs listed state that it has an output of 78mW, 3.65dB gain, and an output impedance of 0.2Ω These numbers don't mean anything to me, and again, they may not represent this unit anyway.
Question is, do I run the risk of hurting the bike's stereo amp by using this headphone amp between the MP3 player and the aux input on the stereo? Obviously, the thing is designed to output to stereo headphones, not into another power amp. I have held off trying it out of an abundance of caution; while someday I will probably want to put a modern receiver with Bluetooth, USB etc into the thing, that's a future project due to the price tag. For the time being, I'd like to be able to use the haedphone amp if possible.
Newey, I deal with Class D amps all the time. You won’t damage anything as long as you run the audio out from the first amp to the audio in on your second amp. The biggest problem I foresee is the power to amp. The little milliwatt amp runs at just milliwatts. It’s power source must be a very low voltage. Typically a 1-3 watt amp needs 3.5-5volts of power. And you’ve got 12 volts running from the bike battery right? You’ll need a step down converter. If it were me, I’d run a higher wattage amp on 12 volts. A step down converter to a higher watt amp may fix your problem; i.e. 12 volts down to 5 volts into a 3 watt secondary amp. www.adafruit.com/product/3006
I agree with frets, should be fine, you just need the right lead, maybe a 3.5mm stereo patch cable?. I've plugged MP3 players into lots of things. When Im doing it, I often want to take a stereo output into a single mono input such as on a mixing desk, and for that I add a couple of resistors inline so Im not shorting channels to each other. But Im assuming you'd be doing stereo to stereo, so that issue wouldn't come up.
On power supply, probably best to let the MP3 and Fiio amp run on their own internal batteries.
Then its just a matter of loading up some Steppenwolf on a loop.....'get yer motor runnin',...…..head out on the highway!'
Yeah, the MP3 player and the amp both run on internal USB-rechargeable batteries. The amp gives about 13 hrs of runtime, so recharging shouldn't be an issue, I couldn't ride for more than 13 hrs if my life depended on it.