answered
2015-09-09 02:15:41 +0200
simo 29079 ●345 ●466 ●481
Jolla has an audio jack designed for headphones, not a line out designed for amplifiers. I don't know the exact values on Jolla, but typically headphone jack has a low (8-32 ohm) impedance, compared to hundreds (100-600 ohm) in a line out connector.
- Headphone jack to headphones: Few ohms impedance from the source is driving few ohms headphones. Matched impedance values are the best for the battery life. Professional headphones have some more impedance, typically resulting as better sound quality but lower max volume.
- Line out to amplifier: Few hundreds of ohms impedance (line out) is driving 10000 ohms input (line in). The idea is to drop the load to minimum, delivering an easy signal just strong enough to measure to pressures (voltage difference), and amplify that (add more load) in the destination.
- Headphone jack to amplifier: Low impedance in the source meeting high impedance on the destination reduces the frequency response, tailored in the phone for matched (or closed to matched) impedance. Additionally, compared to line out, headphone jack has it's own noise coming from the headphone amplifier chip and the volume control. Even worse, mobile phone provides very low Vpp (peak to peak voltage), making measuring the pressure a challenge to the amplifier. Depending on the quality of the amplifier, it's own noise might become audible, especially if the volume needs to be set high. In the end, there might be three different quality reductions, in the worst case resulting as low bass not audible and noise added from both the source and the amp.
If the amplifier is a quality one, I'd try with 1/3 - 1/2 volume setting on Jolla (to reduce the signal noise to minimum) and higher volume setting on the amplifier.
If the amplifier is a low-end (car stereo), I'd suggest adding resistors (maybe 600 ohm serial, 100 ohm paraller) into the wire to get closer to typical line out impedance levels, aiming for a signal that the car stereo amplifier is designed for. Sound quality gets better, but notify very low max volume. Powerful amp required.
The best solution: Get a car stereo with Bluetooth audio. Digital signal doesn't mind the impedance ;)
Is the phone connected to its charger at the same time
rsainio ( 2013-12-30 10:27:53 +0200 )editNope! Granted, it sounds a bit like grounding buzz. Tried with an external mono speaker and no problems there. Someone else had a similar issue when connecting to car stereo (link in finnish) here
J_W_PEPPER ( 2013-12-30 10:54:37 +0200 )editI'll add to this that I was using the stock media player and FLAC audio file for playback. Haven't actually tried it again after the "Maadajävri" update. Will do so today.
J_W_PEPPER ( 2013-12-30 11:41:21 +0200 )editOh and I was afraid it might be just my phone. Yes, same here, headphones seem to be fine, car audio has very bad distortion going on, with the stock player as well as android GoneMad Player. Tried two different cables, same result, though it seemed that by turning the plug in the jack resulted in different kinds of distortion, one instance of really really quiet sound and on one occasion actually distortion-free, fine audio. I am swamped with work, so I couldn't test this more.
Ozymandias ( 2013-12-30 14:17:43 +0200 )editTested it again, same setup: not connected to charger, only 3,5 mm to aux extension, same result. The frequency was higher than I remembered. White noise, like a detuned radio. Tried turning the plug like Ozymandias, but no difference. Only some loud pops and contact noise.
J_W_PEPPER ( 2013-12-30 19:21:46 +0200 )edit