Sled cabling

I was looking at feeding something through the Line In this weekend, and since the line in is only connected on the rear feature connector, this could only be done by mounting the unit in the sled (I still haven't fitted it to the car yet).

I then looked at the output - and woke up to the fact that (as Hugo has mentioned) there are 4 quasi-differential outputs from the sled, not the two simple, earth referenced stereo connectors popping out the back of the unit itself. Upon connecting only the two "front" output connectors to my amp, I got pretty horrible sound due, to the earthing/referencing used when the unit is inserted in the sled.

Hugo, could you explain (for a thickie):

1) How can I connect up to my simple stereo from the sled in order to get a good stereo image on playback
2) What do you mean by "Quasi differential" outputs?

I suspect this is due to my mis-understanding of the earthing reference used by the unit when inserted into the sled, as distinct from the earth-referenced output of the stand-alone unit. I would be interested if you could get a bit techincal here, as it would help!

Rob Schofield

If you're using the unit in a car, the output's ground will be near 0v - not quite, due to the fact that it varies around the car, but close. If you want to use the 4v outputs with a home amp, use the grounding cable and short the ground lead to the empeg case, which should correspond to mains earth (as the PSU is earthed).

The o/p's are quasi differential as they aren't actual differential drive, just single ended, but with reference to a ground sense. If this ground sense floats then things can get wierd, as you heard!

Hugo

Thank you, Hugo

Following Hugo's answer here, I connected up my empeg through the sled to my home hifi and fed an external source to Line In. The wiring was successful - I got excellent sound at the speakers and could successfully change source between the empeg and the external source.

BUT, to my great disappointment, I discovered that - the visuals don't operate in any other mode than MP3. Both Radio and Line in sources give you just a blank screen, regardless of visual setting.

This tends to imply that the visuals are fed by the MP3 player application only, rather than by the "output stage", and are therefore not independent of input source.

This is a real shame; although some of the visuals do have track info as part of the main display, some of the others do not rely on it and give a dynamic response to the music. Surely it would be more interesting to have these graphics available for the radio and Line in also?

Hugo, any plans to change this so that visuals are active on *all* input sources?

The sound selection is within the DSP: there's no high-bandwidth path to the DSP, as it was designed to be used with the average microcontroller you find in a car radio :(

There's a possibility we could get visuals on line-in, it's just the sound input via line-in is more a by-product than a design feature and has never been tried :)

It's not high on our to-do list, but we'll get to it when the more important things have been done.

Hugo