I got on this forum looking for line-out cable info and this is my first post. Inspired by 14124all’s work (thanks!), I’ve been performing some experiments on my Fuze, using a voltmeter, power supply, and oscilloscope. FW version 01.01.11A.
First, the Sandisk cable connector: there are two little rectangular holes on the back (non-logo) side, and two hooks
extending into the holes from the front side. The hooks hold the halves of the shell together. If you can get pieces of
shim material or similar to fit snugly down into the holes, they should press the hooks out of the way, enabling you to
separate the halves without breaking off the hooks. The hooks on my connector broke. The solder on the PCB is RoHS-compliant
and did not stick to my 30-gauge test wires well, so I wicked it out with fine solder braid and applied some good old-
fashioned tin-lead stuff.
Now for my electrical measurements. Pin 7: the line output switches on with 1.82 V and higher on this pin (I tested up to
3.3 V). The input resistance of pin 7 is 9.1 kohms with Fuze power turned on; higher with power off. Line out AC
amplitude is not affected by pin 7 voltage, other than being switched on and off.
Headphone output: 0 V DC offset. Output impedance of the headphone amplifier is approximately 20 ohms. Level into
a high-impedance load, with volume setting on max and “system setting” = High, is the same as that of the line output.
But of course as others have said, to get this level you must crank up the volume setting, and remember to turn it back
down when you plug your headphones back in.
Line out: 1.44 V DC offset. I saw a maximum AC peak-peak output amplitude of almost 2 V, which
corresponds to 0.7 V rms (by the way, what do you guys mean by rms p-p? Is this the same as rms AC?). Output
impedance is very low, on the order of 1 ohm or so (I didn’t load it down enough to measure really accurately out of fear
of blowing the amp). Output level is constant with volume settings above 1/4, and not affected by the “system setting”.
This definitely is not the same amplifier as what drives the headphones, even though the max amplitudes are the same.
Equalizer: line out is affected by the equalizer. I found that when using “Custom EQ”, if I increased all the frequencies
equally, the amplitude went up but flatness became worse. With 0 dB settings, flatness was 0.5 dB from 50 Hz to 6 kHz,
and 1.5 dB out to 20 Hz and 16 kHz (the limits of my test tones). With 12 dB settings, peaks occurred at 400 Hz, 1.25
kHz, and 4 kHz, with 4 dB difference between the peaks and the adjacent valleys. Even though the 0 dB setting
produces a lower level, the fidelity is better.
When I drive my car stereo with the Fuze’ line out, the volume is somewhat lower than that of a CD, but not significantly.
In my application, it is better to change the volume on the stereo than to mess with the equalizer settings.
USB 5V: if I plug the USB cord into a PC, both the headphone output and the line out are turned off. But if 5 V is applied
through the USB cable while the data lines are left unconnected, the Fuze outputs music via either output, while it
consumes 300-350 mA and indicates it is charging. This means a single car cable can be used to provide line out to a
stereo, and charge the Fuze at the same time.