Sorry for waking an old thread but I have new information to share that might be of interest to some of you.
I have known for a long time that the D2 A8/S8 Bose amplifier is pin-for-pin compatible with the 2000-2002 B5 A4/S4 (sedan*) unit, and is also mount-compatible. But I have read mixed results from various places including this thread. I have been on the lookout to purchase the D2 unit to try, but it seems that (at least on eBay) most of them are in the UK and the shipping cost leaves a bit to be desired. As luck would have it, one came up for sale in a facebook group that I belong to, and it's located not far from me, so the shipping cost is minimal. I bought it and within 2 days it was delivered in great shape.
* Someone correct me if I'm wrong, but looking at the Bentley repair manual wiring diagrams for the Bose systems, the Avants appear to have quite a different setup, and might not even use the 8D0 035 225 A amp at all.
The basics: I have a 2001.5 Audi S4 sedan with Bose option. The stock Bose amp part number is 8D0 035 225 A. The D2 Bose amp I purchased has part number 4D0 035 225 (no suffix). Many people used the latter with C suffix but I don't know if there is any substantive difference. My car was originally equipped with the Symphony I radio, but I had retrofitted a RNS-E (8E0 035 192 J) Navi Plus instead.
For simplicity, I'll refer to the S4's stock amp as "stock amp", and the A8/S8 unit as "new amp" from here on.
Because I'm an audio engineer, I want to see real data just as much as I rely on listening to evaluate any piece of audio equipment. Thus after I removed the stock amp from the car, and before installing the new amp, I put both of them on my test bench for some frequency response measurements. This is important because the equalization curves are different and will impact how they sound. I used my Audio Precision SYS2322A Dual Domain audio analyzer to perform the measurements. I measured each of the six output channels on both amps. I used a bench power supply dialed to 12V DC, and connected the +12V to both pin 13 (power) and pin 25 (switched positive from radio), and the ground to pin 24. On both amps, pin 11 is also ground, but on the B5, the car's wiring harness ground goes to pin 24.
For the measurements, I set the Audio Precision's analog output channel 1 to produce a 1Vrms output signal, which is swept from 20KHz down to 20Hz. This signal is fed into the inputs of the amplifier, and then the output of the amp is then captured by the Audio Precision's analog input 1 for analysis. The output channels are done one at a time. The results are as follows. I am only showing the right channel results here because the left channel is identical (except for the left rear, but I'll get to that later). The vertical axis of the graphs is set with a fairly high resolution (2dB/div) to illustrate deviations from flat prominently.
All graphs, except where noted, is the stock amp on the left, new amp on the right (If your browser window isn't wide enough to show both graphs side-by-side, then they will appear stacked, the stock amp on top, and the new amp on bottom).
Right Front output (for right door speakers including tweeter):
Comments:
- The gain of the stock amp (at flat ares of the curve) is just a hair under 16dB, the new amp is slightly higher than the stock amp, by about 0.5dB.
- There is a bass rolloff, starting a little lower in frequency on the new amp but cuts off at a steeper slope than the stock amp. This helps to protect the speaker from excessive cone excursion and potential damage.
- There is a notch at around 1.2KHz on both amps, but on the stock amp it's about 3.6dB deep whereas on the new amp it's about 1dB.
- This notch is probably to equalize an opposite bump in the speaker's frequency response, but the amplitudes here are not huge.
- The stock amp has a flat high frequency response, but the new amp has a sharp boost in the upper treble region, leading to a peak of 8dB above flat at around 15KHz.
- The treble boost is a good thing for the B5, because I always thought that the stock front door tweeters' were lackluster. When I had the Symphony radio, I adjusted the upper band of the radio's hidden equalizer to maximum and that helped a lot. Now, on the RNS-E there is no such hidden EQ, and dialing up the treble control causes too much boost in the mid-treble region and the high treble was still a bit dull. This treble peak will go a long way toward "fixing" the treble problem.
Note that the vertical scale of the new amp is is 2.5dB/div in order to accommodate the top of the treble peak.
Right Rear output (for right door speaker)
Comments:
- As for the front right output, the stock amp's gain is just a hair below 16dB, the new amp is about 0.5dB higher.
- The stock amp has a bass rolloff below 100Hz, whereas the new amp has it starting at about 150Hz, and is a steeper curve. Interestingly, the rolloff stops and rebounds up to about -11dB from flat at around 50-63Hz, before falling off again below that.
- This shows that the rear speakers will receive less bass energy. I don't think this will be of any detriment to the sound, because even with the stock amp, I found that the rear door speakers to be bass-shy anyway. I like to set the fader to about 10 o'clock position to let the front speakers do more of the work. This gives a more natural stereo image and reduces the amount of boominess from the bass speakers on the rear deck. Sitting in the front seat, the difference of the two rear door speaker curves actually didn't sound at all dramatic.
- On the stock amp, there is a dip in the response at around 400Hz, and about 2dB deep. On the new amp, there is a dip at 1KHz instead, also about 2dB deep. These are not large amounts so the audibility is minimal.
- The rest of the midrange and treble spectrum are flat to 20KHz on both amps.
Right Bass output (for right rear deck speaker)
Comments:
- It's obvious that on both amps, this output is meant to be a bass-only channel with most of its output in the low bass region. On the stock amp, the bass plateau is 32Hz-60Hz, on the new amp, it's 32Hz-70Hz. But on the new amp, the gain of this frequency region is about 1.5dB higher and flatter.
- Above the low bass region, the two amps exhibit vastly different response characteristics.
- On the stock amp, it dips to -9dB from flat at about 180Hz, then rises again to -4dB at around 500Hz. Then it falls off quickly above that.
- On the new amp, it dips to -6dB at 100Hz, but rebounds to -5dB at 150Hz, then goes into a shallow drop above that to a minimum of -13dB before rising to a treble boost of about 4dB at 20KHz.
- The reble boost is probably of no consequence on the B5 rear deck speakers, because they are woofers with non-existent high frequency response.
- The 100Hz to 400Hz area is interesting, because the two amps exhibit just about the opposite behavior. The stock amp is a trough whereas the new amp is a bump, although both are in low amplitudes. I think the result of this is that whatever low frequency loss there is in the rear door speakers (between the stock and new amps), it's made up for here. The new amp's missing peak at 500Hz should probably help to make the low-midrange region a bit cleaner.
I mentioned above that the left channel graphs are the same as the right channel graphs, except for the rear door speakers on the new amp (the stock amp has identical curves left and right). The left graph below shows the left rear output while the right graph shows the right rear. The right rear is already shown above, but repeated here for ease of comparison.
New amp only: Left Rear vs. Right Rear output (for rear door speakers)
Comments:
- I already described the right rear response above. Compared to the right rear, the left rear's frequency response has a similar shape with a bass rolloff and the midrange notch at the same frequencies.
- However, in the bass region, the left rear has about 3.5-4dB less output than the right, and in the upper midrange to 20KHz, it's 6dB less.
- This creates a channel imbalance, which is curious. At first I wondered if this was an anomaly, so I retested several times and got the same results. I also thought that it might be due to a malfunction. But after checking other performance parameters and doing listening tests, I now think that this is by deliberate design. When sitting in the driver's seat, the far side rear door speaker has more output, but the near side door speaker is closer to the ear so they actually sound well balanced.
Before the bench tests, I listended to a few recordings on the stock amp to establish a baseline of sonic character in my memory. After installing the new amp, I played the same recordings to hear the differences in sound.
One thing that was immediately apparent was the change in treble response. I no longer have to tweak the treble control on my RNS-E to maximum to get the "sparkle" from the front tweeters. The sound is now much more extended in the highs, cymbals crashes have the proper brilliance and attack, etc. Now I set the treble to only 2 notches above flat and I'm still experimenting with the optimum setting, because different recordings vary. But in my opinion this is the biggest improvement by swapping the amps.
The next thing that is almost as dramatic is the cleaniness of the sound, particularly when the volume is turned up. I think the 80W output of the stock amp vs. 200W for the new amp is at play here. Since the amp has 6 outputs, and the gain is approximately the same on each of them (ignoring some small dips and the treble peaks from the EQ), it's fair to say that the output power on the stock amp is 13.3W per output, whereas it's 33.3W per output on the new amp. Neither of these are big numbers, but keep in mind we're driving 2 ohm speakers, so the equivalent SPL is twice that on a standard 4 ohm car system, assuming the same speaker efficiency. The new amp's added power means that even when you crank the volume up, you are much less likely to drive them into clipping. The amplifier will operate in a low-distortion zone for cleaner sound.
The bass response, surprisingly, also sounded better than the new amp. It's not more or less bass, it's the quality of the bass that is improved. I think there are several factors at play here:
1. The steeper rolloff of the response at the front door speakers eliminate sub-bass cone movement, so there is less modulation of the midrange frequencies. There is no perceived loss of bass at the front speakers. In fact it sounds just as strong or perhaps slightly stronger than stock. Just don't expect to hear 32Hz notes from a pipe organ or synthesizer.
2. As mentioned above, the higher bass rolloff frequency at the rear door speakers is more than made up by the rear deck bass drivers. The bass drivers are driven with slightly more gain and a different upper bass response that tends to "fill in" where the rear door speakers leave off.
3. Higher amplifier maximum power output.
Overall, I am very happy with the swap. Your mileage may vary of course, depending on which radio you have, whether you still have the stock speakers, and which version of the D2 Bose amp you have (not sure if it makes a difference). Without ripping apart the system and doing major surgery on wiring, and mounting aftermarket amps and speakers, I think this mod is a good bang for the buck. It is also a simple installation, and keeps everything factory and tidy.
http://www.tikan.org/ti/audi/autiq/bose_amps.jpg
Originally Posted by crc364
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