HK Amp Swap

Pros: Easy Upgrade, Maintain Warranty
Cons: Just a moderate upgrade
Cost: About $40 (price depends on seller)

The Environmentally Correct Stereo Upgrade


Please don’t throw those HK amps in the dumpster!!

I’m not certain how it came up, I think it was Robert’s idea. He wondered if there was a way to use the vast number of Harmon Kardon amplifiers that have been removed during the stereo upgrades by members of the Message Board. The idea was to replace the stock amplifier with the HK amp. I volunteered to use my 3/96 production 1.9 Z3, one of the very early production cars. It does not have rear speakers or a sub woofer. The only stereo upgrade that has been performed on my Z is a set of MB Quart QM130TX3 5¼ in. front kick panel speakers. The improvement that these speakers made is chronicled by Carter Lee in his column here on MZ3 Net.

You will need a few hand tools to perform the swap:

10 mm socket

short extension


large flat tip screw driver or

trim panel plug removal tool

You remove the carpet trim from the front of trunk by removing the black trim plugs. Locate your amp: on early cars its located in the upper left front of trunk, on later cars it’s in the upper right front. Using the 10mm socket, extension, and ratchet remove the three nuts that hold the mounting bracket to the body. You then unplug the two connectors from the back of the amp. There are three 10mm nuts that hold the amp to the mounting bracket, remove these. Place the amp in a safe place. The installation of the HK amp is the reverse of the removal. This is an exact bolt for bolt swap, nothing to modify! Total time for this upgrade 30 min., a complete no-brainer! There is one remaining plug on the HK amp that remains unused, I am told this is for EQ changes related to the speed sensitive volume. But the amp works just fine without this connection (which is a good thing since older stereo setups don’t have this wire).

Now the results. Bass is much better, feels about 30% better. Measurement done by the bass-o-meter (my left foot on dead pedal). Highs are about the same. Tried increasing the treble but not much different from original amp. The most noticeable change is the lack of distortion in the upper volume ranges. The original setup would flake out at volume levels required at 70mph. The HK amp allows distortion free sound at speeds up to 85mph.

Is it worth it? In a word, YES! For those of us who are not the audiophiles this is a very cost efficient upgrade. In my case the hardest thing to do was empty the trunk. At the 1999 Homecoming there will be a new contest to go with the autocross, the POS Amp Toss, you can use it there. Now all you true audiophiles who have upgraded to an aftermarket system now have a market for your old amps, and we will have enough of the old amps for the POS Amp Toss at 99 Homecoming.

In an attempt to match HK buyers up to HK sellers, I recommend you post on the BMW roadster message board, Robert and I agreed upon a $40 price for the HK amp so I recommend you start the buying/selling negotiations there.