I simply wanted to use my CDs. The tape deck just did not cut it for me, nor did the weak power output of the head unit to the OEM paper speakers. I also had OEM headrest (HR) speakers which sounded very weak at highway speeds with the top down. I did come across Jeff Anderson's OEM head unit service, and many miata lister's swear by its effectiveness to bring out more vibrant sounds and help fix HR problems (more on that in a bit), but since I wanted a CD, the OEM unit had to be yanked.

I did run into some problems along the way to solve my audio craving, but they were mostly the result of the terrible OEM wiring. Again, more on that in a bit. Below is the installation brief I wrote for miata.net for the Alpine head unit I purchased.

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The 7833 is the bare-bones model in the Alpine line. Its features a single disc CD player in the head unit, 4x35 power output, AM/FM tuner, and can control an Alpine 6 or 12 disc changer. There are no pre-outs on this head unit. The face plate is removable and ships with a plastic carrying case.

I purchased the 7833 from Bryn Mawr Stereo, a chain of stores in the PA, NJ and Delaware areas, for $199. I selected the alpine for 2 reasons:

• The head unit is very simple and does not have a busy display. I think this matches the simple, clean dash layout of my miata
• The head unit is relatively inexpensive and has a removable face plate. No need to put something too nice in a miata that is driven everywhere. I was going to go with an Eclipse head unit, but even with their 1 year anti-theft refund warrenty, its always in your dash and bait for a stupid thief.

I have a ' 92 with a base radio. Installation with the wiring harnesses was fairly simple. I began by popping the eye vents out (3 and 9 o'clock with a tiny flathead screwdriver). The stock radio comes out fairly easily, with the one exception being the ground wire attached to the rear of the head unit. Its a tight fit to get your hand back there with a stubby screw driver to undo the one phillips head screw. Small hands are good here. The challenge here came in the re-assembly. The Metra kit is functional, but it is universal. I highly recommend having a Dremel on hand, as *many* little plastic tabs must be trimmed off the Metra kit for the Miata. Additionally, my kit did not quite fit in the space vacated by the stock mounting harness. I had to use the Dremel to round the lower corners a bit and force the harness in so that it would mount flush against the dash.

My final problem was the head unit itself. The Alpine does not have that wide of a face plate, but it still was too wide for the Miata's dash cover to fit over it when it was installed with the Metra kit into the dash. So I had to pull the head unit out, unclip the wiring harnesses, and reassemble the dash without the head unit in the mounting harness. When everything was complete, I slid the head unit in and it locked nicely, mounting just about flush with the dash. I will say its possible that the reason I could not get the dash cover around the head unit the first time was that I had not rounded the lower edges of the mounting harness enough to get it to lay flat against the dash, so the angle was preventing the dash cover from returning to its proper position. Considering there is no room to reach behind the miata dash from the floor, I also did not use any rear mountin bar as is sometimes used with car stereos. The Alpine fits extremely snugly into the 7501 mounting kit.

My patience did reward me with a head unit that outputs clean CD and radio sound with a better power rating then the stock head unit. I have stock door and head rest speakers in my '92. The Alpine outputs cleaner sound, a bit more bass, with a richer overall sound then the stock head unit IMHO. Speakers are still a weakness of the overall system, but its not a bad as it was with the stock head unit. For now, I don't see myself needing new speakers as I can hear my tunes just fine with the Alpine :)

Don't forget to re-attach the wiring harness for the hazard and head light pop up switches. This will cause your headlights not not work at all. I was quite shocked when I realized I forgot this small detail, and a bit annoyed since I had to disassemble the entire dash to get at that switch (you can not get at it any other way). The switch has very little slack, so its easy to forget its there in the excitement of putting it all back to test out your new system.

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With my Alpine in, I was jamming! However, I quickly found out that Mazda may have let an intern design the stock wiring harness for the radio and HR speakers. I wired up my speakers in parallel for better sound. As with most HR speakers, the OEM ones have a 4ohm rating. However, when I used a voltmeter, I measured a bit less. This is not surprising as 4 ohm is a reference number, not an exact measurement. In theory, I was driving the 4 HR speakers off of 2 channels from the amp in the headunit. This meant each channel saw 2 ohms of resistance, which is below the rated 4 ohm load of most head units. Two 4 ohm speakers in parallel net 2 ohms resistance as R(sum) = 1 / (1/R1 + 1/R2 ... + 1/Rn). Few devices are 2 ohm tolerant, although the miata head unit would seem to be as it works with the HR speakers just fine. Considering I was only driving very small speakers, the extra power sap from the 2 ohm loads should have been small. However with this Alpine, that was not the case.

If I listened to music for 1/2 hour at decent volumes the head unit would get too hot, and start to clip out. This was the self-preservation mode kicking in on the alpine circuitry (clever, I must say). I did not want to run the HR speakers with an inline amp (remember, the head unit has no pre-outs), so the only solution was to run the speakers in serial. This would show each channel an 8 ohm load with respect to each pair of HR speakers. Not optimum as far as sound quality and balance, but it would do the trick. So I merrily began the wiring process. I should have known this would be a problem.

The OEM HR speakers don't have any speaker leads visable to the casing. Two wires snake into the plastic case and attach to the terminals of the dinky 3.5" speakers. 4 small screws mount the square paper speaker to the plastic case. However, the speakers also have a bit of glue on the edges, so getting them out of the case is not an easy task. In the process of doing it (2 times since the wiring harness was not correct...I am getting to that part :) I ended up cutting 2 of the paper cones a bit. The net effect is trashing the speaker, which prompted me to get 2 pair of Rockford Fosgate 1203 3.5" speakers which had nice normal terminals to connect speaker wire too.

The reason I said I had to undo the OEM HR speakers 2 times is that I relied on the OEM wiring harness color coding to be accurate. Silly me. The first time I wired up the speakers in series, I still had problems with the Alpine overheating. After a bunch of cursing, I undid the seats one more time and began to trace the wiring harness. This was not an easy task, and involved lots of cutting of black tape which wrapped the OEM harness in many places. In the end, I found that the color coding of the wires was merely a ploy by Mazda to think they know what they are doing. The wiring was severly crossed, and I was amazed that anything was working in the first place! Fairly aggrevated at this point, I yanked all the HRs out myself, and ran my own Monster (tm) cable to all the HR speakers. This was a PITA as I had to feed the wire up the seats with a coat hanger, but it was the only way I could be certain of the polarity of the wiring. I have never had the Alpine cut out on me since.

To finalize my system, I yanked a pair of Infinity Kappa 62i speakers from my OTM and planted them in the doors of Tatjana. I did not have an actual mounting cover, so I used one of the OEM holes, and drilled 2 more to help mount the speaker. Had I been more patient, I would have looked for some sort of plastic mounting shell that would allow the speaker to me mounted a bit deeper in the door (I think this is what PBC sells with their Infinity Speaker kit, for example). By simply using the sheet metal, the tweeter of the Infinity speaker poked out a bit, and clipped the plastic cover. Some diligent work with the Dremel solved that problem by snipping some of the backing from the plastic cover, but this was not the proper solution, just the quick and dirty one.

Had I to do it all over again, I probably would have looked for some 8 ohm rated HR speakers, which in parallel would be 4 ohm loads to each channel. I believe the MAX speakers offered by PBC meet this requirement. I also would not have been so lazy and probably have gone with a CD changer. There are several vendors on the Net that sell refurbished equipment (considering the warrenty on new equipment is only a year, refurbs are not that bad of a deal) and one can get a head unit *AND* changer for $250 pretty easily. I used Spidergear to get a Denon CD changer for my OTM that had kicked the bucket. A lot less expensive then servicing the unit from an authorized repair facility.