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Friday, November 21, 2014

Doug's Domain

Doug Vetter, ATP/CFI

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Wednesday, December 7, 2011

Stereo Headunit Problems

Nearly five years ago I replaced the OE stereo headunit with a remanufactured unit for around $160. While I have long wanted to install a better audio system in the car, if you've been reading this site for any length of time you probably know that I have had higher priorities – then as well as now.

About six months ago a reader chimed in with a stereo-related question and mentioned his parts supplier was unable to get a replacement headunit from BMW as they were officially unavailable (ENDED in BMW parts parlance). So you can probably imagine the dread I felt when I recently started to notice my headunit's volume control acting up just like it did five years ago. Now when I turn the volume knob it often does the opposite of what I want (turn volume down, volume actually goes up and vice versa), works erratically (requires an inconsistent number of spins of the knob to change the volume a given amount), or not at all (makes me want to put my fist through it).

I called my parts department in a first effort to correct the problem and they confirmed that the units are no longer available in either new or remanufactured form. That left me with a couple options:

  1. Try to repair the radio by replacing the most likely cause of the problem -- the rotary encoder.
  2. Bite the bullet and install an aftermarket headunit.

I'm all for a challenge and an opportunity to save money but I quickly ruled out the repair idea primarily because of the low probability of finding a compatible part for a radio that hasn't been manufactured in over ten years. That led me to realize I'd need to search for a suitable aftermarket replacement.

Headunit Research

As I reviewed what currently passes for mobile audio headunits I grew increasingly depressed because they all seemed to suffer from the same problems I've screamed about for years:

So it shouldn't come as a surprise that I was only able to locate two headunits in the entire car audio market I'd remotely consider: the Parrot Asteroid and the Pioneer DEX-P99RS.

Parrot, perhaps best known for its radio control technology, released the Asteroid only in October so it's very new to the market. It runs Android and allegedly allows embedded developers to tweak the OS, which is a refreshing change from the closed and proprietary systems of the major audio equipment manufacturers. The unit lacks a CD player and that allows it to be half the depth of the normal DIN specification -- clearly an advantage when dealing with the wire bundle behind the unit. The problem with the Asteroid is that it's new and I've heard reports (subjective as though they are) that the sound quality isn't great, there are RFI issues with the display, and the firmware needs work. I don't have the time to do Parrot's field testing so that leaves the DEX-P99RS.

I must admit I've never been a fan of Pioneer equipment as they were always known years ago as a “consumer” option rather than an audiophile's choice, but this unit has a lot going for it:

The downsides are:

Amplifier Research

Like all high-end headunits the DEX-P99RS lacks internal amplification. For most audio enthusiasts that's a perk but for me it just means I'll be forced to swap out the factory amplifier at the same time.

Special capabilities of the P99RS create a dilemma: Do I leverage the power of the on-board DSP and use active filtering along with two four channel amplifiers to drive my components, or do I go the traditional route and send a full range signal back to a single four channel amp and use passive crossovers? While I know active filtering is more flexible and avoids all the coloration inherent in the passive components in traditional LC filter networks, the reality is I don't think I can justify the cost, weight, and complexity of a multi-amp system. So at this point I'm sticking with my original plan for a four channel amp in combination with passive filtering.

I did my share of research on the current state of the amplifier market and Arc Audio seems to be the way to go. Many of the their amps are designed by Robert Zeff (who founded Zapco and still designs many amps for well-known name brands under the Nikola Engineering banner) and fortunately several of the smaller units including the 75Wx4 K300.4 would fit nicely in the location of the stock amplifier. But the choice of amp can't (unfortunately) be based on size alone.

BMWs are electrically noisy vehicles and as such benefit significantly from the use of differential signaling between the headunit and amplifier. Arc Audio makes the “Audiophile Line Driver” or ALD, a unit similar in function to the Zapco Symbilink converters. The perk of the ALD is that they use common CAT5 twisted pair cabling to interconnect the amp and headunit. The downside is that only the SE 4100 (twice the cost of the K series and roughly equivalent to the Zapco 360.4 I priced some time ago) can directly accept the output of the ALD. The fact that the ALDs are not included with the amp is another annoyance, but at $120 MSRP (two required in my case), they are priced within the realm of reason and will be worth every penny if they prevent annoying hum or impulse noise from treading on my music.

The Complete Solution

By now you probably have a pretty good idea that the plan is to mate the Pioneer DEX-P99RS with the Arc Audio SE 4100 using two of the Pioneer's outputs (low and mid, probably) configured for full range output (filters disabled), each connected to an ALD to drive the "front" and "rear" inputs of the amplifier.

The ALD design allows use of custom-wired RJ45 connectors to route the signals from two ALDs over a single CAT5 cable I'll likely route through the center console and existing penetrations in the body to the amp mounted to the bottom of the rear deck. I'm not exactly clear on how I'll mount the amp to the deck, but simplicity may win over maintenance access. A simple shelf slightly larger than the amp combined with some standoffs and a few nutserts will get the job done.

Outputs from the speaker terminals of the amp will route to a set of passive crossovers mounted where the stock amplifier is now, as that is where all the vehicle speaker wiring presently terminates. And speaking of crossovers, I'm planning on using a CDT 2-way specifically designed to mate the CDT 6x9 sub and 1" tweeter, but I haven't figured out what to do with the front set yet. I would really like to keep the three way arrangement in front because I think that lends to a smoother midrange, but cost may win out, as the 3-way CDT crossover I could apply here is ridiculously expensive.

This is clearly a big and costly job, but that's not the half of it. I'm not really in a position to do the work until next year because the E46 doesn't have winter tires on it so I can't take the E36 out of service for an extended period of time. So that means if the volume knob doesn't last another 4-5 months, I may be forced to install the Alpine unit I pulled from the Acura before I sold it. The upside is that I now have at least a reasonable justification for a new audio system of some kind and I'd be lying if I said I wasn't looking forward to the end result. Stay tuned.

Mileage: 215200