4D0035225C == Audi A8/S8 200W Bose Amplifier = Plug-n-play for our cars

[ColinGruenfeld]

So there has been a lot of hype lately about these factory D2 A8/S8 Bose amplifiers (Part Number 4D0035225C) being installed in our cars. I would like to compile some information here before I decide to buy one.

These amps are apparently 200W, compared to our factory 80W.

However, is this for all speakers, or for just the 2 rear subs?


Also, for anyone who has upgraded from a factory Bose B5 amp, to one of these amps:

Was it worth it?
What kind of difference did you notice?


Thanks in advance.

[ColinGruenfeld]

MODS: Can you please change the part number in the title to: 4D0035225C

[mholme]

The amp supplies all the speakers, so it's not just the rear deck speakers. There is a significant improvement in sound with one of these amps..for a factory, 12+ year old piece of equipment. I mostly noticed the gains at high volume level when the GALA signal starts adjusting for speed, the sound usually fell on it's face, the D2 amp prevents this. If you're staying stock, they are definitely worth it.

[ColinGruenfeld]

For the record, I have 4x Infinit's and 2x JL 8" Subs.

I had removed my rear 2 subs, which is why I asked this question.... It wouldn't make sense to purchase this item just for the rear subs when I don't have any.

[bmoreS4]

....I would think that this amp plus new 2ohm speakers would make a real nice upgrade.

[ColinGruenfeld]

Just bought mine for $50 + S/H

[bmoreS4]

Just bought mine for $50 + S/H

where from?

[B5S4/C5A6]

Just bought mine for $50 + S/H

see this is what I am talking about. Dude in the classifieds just doesnt get it. Oh well. Glad you were able to find one.

[cjk]

where from?

2nd

[GWerks]

see this is what I am talking about. Dude in the classifieds just doesnt get it. Oh well. Glad you were able to find one.
[>_<][>_<][>_<]

That ad just came to my mind. LOL

[B5S4/C5A6]

im guessing an Audi Dismantler site.

here are two in MN for $85.. phone number included.
1999
Radio
Audi A8 BOSE AMPLIFIER, 4D0 035 225 C $85 Pam's Auto - MN(St-Cloud) 1-800-560-7336

1999
Radio
Audi A8 BOSE AMPLIFIER, 4D0 035 225 C $85 Pam's Auto - MN(St-Cloud) 1-800-560-7336

[AUDI_S4_ATL]

I bought mine from a 1998 A8 and it doesn't have the C at the end but in the AW wiki it says all D2 with Bose had 200w amps. It is a pretty decent improvement other than the fact I think I may have blown a few of the stock speakers with the enhancement. Anyone using it have some good equalizer settings they want to share? I think mine is set at 8869 8869 right now and it sounds good but it could be better. I just don't have the ears to listen and tune it properly.

[csosnowski]

I'm really curious about this amp, finances prohibit upgraing right now though...

5246 5246, bass, treb and mid all at +2 on the knobs. stock s4 amp. i find that if you increase the values too much then the amp clips and clipping makes square waves=damaged speakers.

also to note, when adjusting the knobs - if bass treb or mid is too far skewed from the rest then sound quality degrades. could be that the symphony head unit has really wide or narrow Q levels for them.

hope this info is useful to someone.

[xccess]

LOL ... you guys didn't read my thread? I did all this last year and can give you some in sight.

that A8/S8 amp indeed 200w compare to our stock 80w. when I change it, it was a very small improve in the sound. it just a little louder. I even had all door speaker change to 2ohms infinity speaker. the rear desk sub also change to 6.5' sub. it didn't not improve any sound in the bass department. I end up swap out that amp and got me Alpine PDX.5, it was big improvement the sound are more alive and the bass kick hard, it not earth shaking, but it was enough bass to turn head from same speaker with different amp. to me that A8/S8 amp not worth the upgrade. but maybe it worth to some people

[ColinGruenfeld]

LOL ... you guys didn't read my thread? I did all this last year and can give you some in sight.

that A8/S8 amp indeed 200w compare to our stock 80w. when I change it, it was a very small improve in the sound. it just a little louder. I even had all door speaker change to 2ohms infinity speaker. the rear desk sub also change to 6.5' sub. it didn't not improve any sound in the bass department. I end up swap out that amp and got me Alpine PDX.5, it was big improvement the sound are more alive and the bass kick hard, it not earth shaking, but it was enough bass to turn head from same speaker with different amp. to me that A8/S8 amp not worth the upgrade. but maybe it worth to some people

I wish that search feature worked :)

[ColinGruenfeld]

where from?

eBay.... Company wanted $95, so I offered them $50.... They took it. Just keep an eye open on eBay and dismantler's websites.

I will post my results here on this thread. Keep an eye, or an ear pealed!

[Gumby]

MODS: Can you please change the part number in the title to: 4D0035225C

Done.

[AUDI_S4_ATL]

LOL ... you guys didn't read my thread? I did all this last year and can give you some in sight.

that A8/S8 amp indeed 200w compare to our stock 80w. when I change it, it was a very small improve in the sound. it just a little louder. I even had all door speaker change to 2ohms infinity speaker. the rear desk sub also change to 6.5' sub. it didn't not improve any sound in the bass department. I end up swap out that amp and got me Alpine PDX.5, it was big improvement the sound are more alive and the bass kick hard, it not earth shaking, but it was enough bass to turn head from same speaker with different amp. to me that A8/S8 amp not worth the upgrade. but maybe it worth to some people

Did you have to cut the factory harness?

[skinnytirez]

ECS wants $1229.32 lol

[VR6Bomber]

Shazaam. got one from Chris at force five for 50 bucks!
I don't think that Force five has ever not had something in stock.[up][up][up]

[B5S4/C5A6]

Shazaam. got one from Chris at force five for 50 bucks!
I don't think that Force five has ever not had something in stock.[up][up][up]

See another example of finding them cheap. Good job. I grabbed mine for $35 plus shipping, from a dismantler in Detroit. They can be had for dirt cheap, no need to pay $180 like the one in the classifieds or $1200 like what ECS is wanting...

[PearlS4]

I got tired of looking for cheap, paid $190. 200 bones is chump change in the world of owning an S4, so I am not to worried about it.

[B5S4/C5A6]

Did you have to cut the factory harness?

No, it uses the same harness, just plug the amp in the same way the stock one was... easy

[AUDI_S4_ATL]

No, it uses the same harness, just plug the amp in the same way the stock one was... easy

The alpine unit is plug and play?

[bmoreS4]

The alpine unit is plug and play?

x2

Would love to know more about this.

[B5S4/C5A6]

my bad, was looking from an iphone and didnt see you were asking about the alpine unit.

[AUDI_S4_ATL]

my bad, was looking from an iphone and didnt see you were asking about the alpine unit.

No problem. I was asking xccess about the alpine unit because he says its better but if its not plug and play most people will probably pass on it.

[B5S4/C5A6]

crutchfield perhaps has an answer

[joespaman]

Crutchfield says they don't have it.

[ColinGruenfeld]

Alright guys, I received my amp today, and installed it in a matter of seconds.

HERE ARE MY FINDINGS:

Audio is certainly more loud.
My aftermarket sub setup hits even harder that before, and is a more clean, punch.
The tone of the speakers has also changed. Nothing a little "hidden equalizer" can't fix.
Highs are more clear

OVERALL:
For $60, I think it was worth it....
I wouldn't pay much more than that though. This is something for those people who are out of things to buy for their cars, or who are going deaf, or would like to go deaf.

[flyingfish2626]

Alright guys, I received my amp today, and installed it in a matter of seconds.

HERE ARE MY FINDINGS:

Audio is certainly more loud.
My aftermarket sub setup hits even harder that before, and is a more clean, punch.
The tone of the speakers has also changed. Nothing a little "hidden equalizer" can't fix.
Highs are more clear

OVERALL:
For $60, I think it was worth it....
I wouldn't pay much more than that though. This is something for those people who are out of things to buy for their cars, or who are going deaf, or would like to go deaf.

I would love to hear the difference Colin...when can I check it out?

[revbjeff]

Pics of subwoofer setup?

[ColinGruenfeld]

I would love to hear the difference Colin...when can I check it out?

Dude! I still wanna take a ride in that Stage III+. Trade? :)

[ColinGruenfeld]

Pics of subwoofer setup?

Coming right at ya... Give me a few.

[ColinGruenfeld]

http://www.audizine.com/gallery/data/500/thumbs/STA70658.JPG (http://www.audizine.com/gallery/showphoto.php?photo=61228&title=jl-audio-b5-custom-sub-box&cat=500)

http://www.audizine.com/gallery/data/500/thumbs/STA70660.JPG (http://www.audizine.com/gallery/showphoto.php?photo=61229&title=jl-audio-b5-custom-sub-box&cat=500)

http://www.audizine.com/gallery/data/500/thumbs/STA70661.JPG (http://www.audizine.com/gallery/showphoto.php?photo=61230&title=jl-audio-b5-custom-sub-box&cat=500)

[revbjeff]

Very clean setup I really like it. I have some RF 8"P3s I need to figure something to with. Are the old deck speaker holes used as ports?

[ColinGruenfeld]

Are the old deck speaker holes used as ports?

Yes. It's an awesome, unique setup. I was fortunate enough to have my brother sell the setup to me. The only downfall with 8's are that the very deep lows don't hit hard at all. Very good for quality of audio, not very good for rap/consistent low level base in songs (ie: dubstep/techno). However, I have come to love them. Each to their own.

[VR6Bomber]

Yes. It's an awesome, unique setup. I was fortunate enough to have my brother sell the setup to me. The only downfall with 8's are that the very deep lows don't hit hard at all. Very good for quality of audio, not very good for rap/consistent low level base in songs (ie: dubstep/techno). However, I have come to love them. Each to their own.

Anything that keeps people from listening to dubstep/techno is fine with me. lol.
I just got my new amp as well should have it plugged in soon.

[ColinGruenfeld]

Anything that keeps people from listening to dubstep/techno is fine with me. lol.
I just got my new amp as well should have it plugged in soon.

Post up your opinion here.

[xccess]

Did you have to cut the factory harness?
No it is plug and play, only things is the carpet may stick out a little due to the amp was thicker, however it not that all great unless you wan stick to stock sound.
As for new Alpine PDX.5, I just tap in to line out put on the stock head unit... search the internet for diagram

[Jurjen]

^^^^ Yep, fits right in, carpet bulges a bit, hardly noticeable.

http://i54.photobucket.com/albums/g113/JurjenHettinga/IMG-20110102-00117.jpg
http://i54.photobucket.com/albums/g113/JurjenHettinga/IMG-20110102-00118.jpg

[crc364]

Really worth it? I see these going for cheap.

[YnotS4]

Totally worth it. It will expose the speakers as a weak link. There is more headroom and deeper base and better high end. Its not ADS or Soundstream etc but much better than the original factory piece

Really worth it? I see these going for cheap.

[crc364]

Thanks man, ill pick one up.

[DynomiteTT]

Anyone know if this works for C5s and TTs too?

I seem to remember the C5, B5 and TT all using very similar bose amps.. I could be wrong

[northcarohio]

Hey sorry to bring this thread back from the dead, but did anybody do this mod and find out that the rear deck wasn't getting the right bass signals? I did this in my 01.5 A4 the other day and it seems like I'm not getting any of the lows sent to my subs. Everything else sounds great but the rear deck isn't getting anything below say 50hz and isn't nearly as loud as the rest. Its still getting sound but its really weak. Speakers and headunit are still stock, and the amp is from a 2001 S8. I also tried adjusting the hidden EQ settings to no avail, and the amp smells fine (not burnt out or anything) and everything coming from the rest of the speakers is clean and clear!

Any ideas?

[HUFset]

Is this also plug n play for non-Bose systems? I can't seem to find the 25pin harness in my trunk.

[HUFset]

Bump for edited question in post #47. Anyone know if non-Bose system is plug n play?

[RicoSuave]

where from?

Can't speak on his behalf, but I would assume any junkyard could source one for you.
Might not be $50, but still cheaper than buying it off someone here.

[ben2401]

Hey sorry to bring this thread back from the dead, but did anybody do this mod and find out that the rear deck wasn't getting the right bass signals? I did this in my 01.5 A4 the other day and it seems like I'm not getting any of the lows sent to my subs. Everything else sounds great but the rear deck isn't getting anything below say 50hz and isn't nearly as loud as the rest. Its still getting sound but its really weak. Speakers and headunit are still stock, and the amp is from a 2001 S8. I also tried adjusting the hidden EQ settings to no avail, and the amp smells fine (not burnt out or anything) and everything coming from the rest of the speakers is clean and clear!

Any ideas?

Had this same thing happen to me... I have the stock bose system with infinity reference in the rear doors, stock 6.5" parcel shelf subs, stock front components, and a kicker comp s 10" sub/hertz hcp1-dv spliced into the line-level wiring harness to the factory amp in the trunk. Up until today I was using the stock bose amp and I just installed a 200w A8 D2 amp. The sound was much, much fuller and sounded properly bassy with the stock S4 amp. The new amp seems to have a way different eq. The only different speakers the A8 has are the front door woofers/subs. Should I try the bose eq grounding wire on the back of my (stock) hu to see if that makes a difference? Surprised it sounds so much worse than the stock amp.

[julex]

That's because:

http://forums.audiworld.com/picture.php?albumid=111393&pictureid=166376

This amp is EQed to not give any bass to pins 20-23.

pins 14-15 are sub out pins for a subwoofer, I don't think S4 has a dedicated subwoofer like S8/avants (S4 avant probably has that!).
pins 1-2 are mono loudspeaker which also gets lows but S4 doesn't have that.

I actually have this amp in my allroad. Fronts get bass, rears don't but my subwoofer takes up the slack there so overall I actually have quite a lot of bass. I don't use pins 1-2 either. I had to move subwoofer pins on my allroad harness to new position since stock pinout was different.

So....not all upgrades are necessarily proper upgrades [:)]

[jbain2]

That's because:

http://forums.audiworld.com/picture.php?albumid=111393&pictureid=166376

This amp is EQed to not give any bass to pins 20-23.

pins 14-15 are sub out pins for a subwoofer, I don't think S4 has a dedicated subwoofer like S8/avants (S4 avant probably has that!).
pins 1-2 are mono loudspeaker which also gets lows but S4 doesn't have that.

I actually have this amp in my allroad. Fronts get bass, rears don't but my subwoofer takes up the slack there so overall I actually have quite a lot of bass. I don't use pins 1-2 either. I had to move subwoofer pins on my allroad harness to new position since stock pinout was different.

So....not all upgrades are necessarily proper upgrades [:)]

Thanks for the info. Did this swap and there was a noticeable loss of the low frequency. Wish I would have come across this first. The avant and A6 (with factory Bose) have separate sub boxes in the rear.


Sent from my iPhone using Tapatalk

[julex]

Thanks for the info. Did this swap and there was a noticeable loss of the low frequency. Wish I would have come across this first. The avant and A6 (with factory Bose) have separate sub boxes in the rear.


Sent from my iPhone using Tapatalk

Either way it will be in effect a downgrade since there will be a loss of bass from rear door speakers regardless of what you do... unless you crack the amp open and try to figure out how to change that, if that's even possible. They are fairly complicated animals.

[jbain2]

Either way it will be in effect a downgrade since there will be a loss of bass from rear door speakers regardless of what you do... unless you crack the amp open and try to figure out how to change that, if that's even possible. They are fairly complicated animals.

Yup. Put the factory amp back in.


Sent from my iPhone using Tapatalk

[ben2401]

Either way it will be in effect a downgrade since there will be a loss of bass from rear door speakers regardless of what you do... unless you crack the amp open and try to figure out how to change that, if that's even possible. They are fairly complicated animals.
Haha damn well I suppose I'll put the old amp back in. Thanks for the great posts man, you had all the info that hours of googling couldn't find.

[R1CH-5100]

This is strange to me. I ran the stock amp like 7 years and when I switched to the D2 amp the sound blatantly much fuller. I had repaired my deck subs years back and with the D2 amp I have to lower the bass setting way down (about 3 notches from the bottom) because its so strong now. I can't speak about the the door speakers loss of bass though. I haven't noticed it as the deck speakers definitely pick up any slack.

I'm probably just not a audiophile, but to me the stock system sounds better with the D2 amp.

[auditechnik]

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):
https://www.amb.org/ap/audi/8D0035225A/right_front.png https://www.amb.org/ap/audi/4D0035225/right_front.png
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)
https://www.amb.org/ap/audi/8D0035225A/right_rear.png https://www.amb.org/ap/audi/4D0035225/right_rear.png
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)
https://www.amb.org/ap/audi/8D0035225A/right_bass.png https://www.amb.org/ap/audi/4D0035225/right_bass.png
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)
https://www.amb.org/ap/audi/4D0035225/left_rear.png https://www.amb.org/ap/audi/4D0035225/right_rear.png
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

[jibberjive]

^^^ Wow, excellent post. Well done.

[auditechnik]

Thanks! :)

[mbagge01]

Does anyone know what the wattage of a c5 a6 or rs6 Bose amp is and if this upgrade to the d2 amp is compatible

[S4James]

any thoughts on using one of the two sub outs on the D2 amp with one of these? 4E0035412A

[LJS]

Sound is a very subjective thing--TRY this 76567656 as a start.
I'm sure you know the numbers range from 1(min) to 9(max) with the factory setting at 55555555
ALSO the OE speakers are a bit limiting---then again the interior of an automobile is not the "best" place for quality sound.
FWIW- I changed my speakers a LONG while ago to a set of 2 ohm Infinity Reference speakers---6032CF for the rear deck, 4022i for the front door and 5022i for the rear door.
I'm not sure these are still available.
I'm surprised these amps are still available on the cheap.

[Spazdoc]

Sound is a very subjective thing--TRY this 76567656 as a start.
I'm sure you know the numbers range from 1(min) to 9(max) with the factory setting at 55555555
ALSO the OE speakers are a bit limiting---then again the interior of an automobile is not the "best" place for quality sound.
FWIW- I changed my speakers a LONG while ago to a set of 2 ohm Infinity Reference speakers---6032CF for the rear deck, 4022i for the front door and 5022i for the rear door.
I'm not sure these are still available.
I'm surprised these amps are still available on the cheap.

So I upgraded my speakers to the same and will do the amp upgrade on a B5 S4 Avant. It sounds like there is an issue with lost bass in the sedan, but is the Avant wired more like the S8 to utilize the sub in the rear?

[auditechnik]

As far as I know, B5 Avants don’t even use this amp at all. They have a different setup including the rear sub.

By the way, there is no bass loss on B5 sedans with Bose. I’m running this amp in my ‘01.5 S4 and bass is fine. See. My measurements in another post above.