TJJ is a stud (or how to get fullrange preouts from DSP audio)

[el_duderino]

Confirmed the following today on a 2005 X5 4.8 is with DSP (thanks and shout out to TJJ for sharing the info assertively!)

(NOTE: This also tells non-DSP folks how I would do an amp upgrade in their cars : )

1) If the tuner in the rear is unplugged, and the HU is unplugged, and then the DSP amp is unplugged, and then the tuner is plugged back in, the system sees the DSP amp is gone, and the DSP function in the menu is ghosted, and then disappears completely.

You lose your 7-band EQ and your (BS) room and echo settings - BUT your steering wheel controls still work.

2) The preout from the tuner to the DSP amp is 10V peak to peak testing with a 0dB reference CD track with a 1KhZ sine wave.

3) The tuner in the rear has R preout pins, unstuffed. We did not stuff them but did confirm that they work with the fader.

4) The output is flat as a pancake (almost - there is a fairly standard auto-loudness bump/tilt in the bass at the lowest volumes, which decreases as volume increases until you get to about 1/2 of full volume. Tested this with a 1/3 octave RTA.

5) We tried various ways to interface with this balanced signal with DC offset:

- Soundgate LOCPREA. This one had tons of volume and very little noise, and it had no noise with the gains turned down. With a lot of gain restructuring we might have gotten ALL the noise out (with the EQ/line driver and the amps, we have a lot of input and output level settings to tweak). But the LOCPREA has transformers in it, and they tend to pick up noise in the X5 out of the air (EMI). This also had a slight peak at 80 and a slight rolloff below 50 on the RTA on its outputs.

- Soundgate LOC4.2. This was one that SG thought would rock, but it had more noise than the PREA. It required a ground loop isolator on the output (SG ISO2) to filter the DC content of the signal. However, the GLI has transformers too, and this was also noisy when we used the GLI, just less so. SG says that we should have tapped it right at the output of the tuner module under the load floor, but I couldnt see a neat way to do that. Too bad - it was flat on the RTA.

- Soundgate LOCB.2. Horrid, don't even bother, SG doesn't recommend it anyway. Didn't bother with the RTA.

- Homebrew. We took a set of RCA cables, hacked the ends off, tapped them straight into the wires at the DSP amp, and plugged them into a GLI to take out the noise. We tried the SG ISO2, which sounded great and had NO noise until we stuffed it into the back of the changer area where it had to go. Then we had noise. We ended up using a Stinger GLI in a metal case, but what I really want for this car is a Jensen ISO-MAX (http://www.jensen-transformers.com/ci2rr.html ). These would reject EMI better than any others.

RTA'd marvelously as described above.

I measured the DC content of the signal and it was about 0.8V at max volume with the sine wave test signal. I verified with others that this should be fine as an amount of DC offset.

6) I also listened to the system. Brief recap: Dynaudio System 240 GT F and R, with custom-made crossovers for the front at 2500 Hz, and a DLS 10" in a fiberglass box. Genesis 75 x 2 amps F and R and a 300W mono amp for the bass.

First off, more output, so more resolution on the volume control.

Second, clearer, more detailed highs, with more sensation of depth.

Finally, more detail and texture to the bass, with some bass notes very clearly sounding different than they did before. Less thud, more texture. It was as if we'd installed a high-end aftermarket CD player - that's how striking the change was. (The customer had many of the same CDs we'd used to tune the system originally).

Overall, the system seemed to be more transparent. I have to ascribe this to eliminating the distortion in the DSP amp output.

He was unhappy that we had removed his 7-band EQ - but he agreed that it was definitely better sounding. He's going to listen to it for a week and come back for some more work (we are sound damping the doors to make the stereo quieter outside the car).

So how I would do any DSP car now is get a set of 1M to 2F "Y" adapters, hack the male ends off, and wire the female ends into the preout wires at the DSP amp. Then I'd plug in the best GLI I could get, and voila - RCA preouts.

If you're doing this yourself, it really pays to find a sine wave test disc and get a voltmeter. It's easy to find sine wave wires with a voltmeter set to AC.

NOTE: SG theorizes that this does not work with X5s with DSP with the digital cable present. I don't give them a lot of credence because they didn't know this worked until I told them, but this *might* not work on pre-2003 X5 DSP systems. Or it might.