Wire Sony HU direct to gutted factory amp?

[onewhippedpuppy]

Is this a stupid idea? Others on here have gutted their factory amp, removing the amplifier portion and retaining the factory crossover. They have then wired a aftermarket amplifier to the factory crossover, and report it sounding very good. What result would I have just wiring the speaker level outputs from my HU to the factory crossover in the same manner? Right now I assume my HU, installed by a PO, is installed with an adapter to retain the factory amp, so my HU is just a glorified tuner and CD player. The reciept lists $40 worth of BMW wiring harnesses, consistent with the price for an amplifier adapter ($30 on Crutchfield).

Most say that the factory amp MAYBE puts out 15W per channel peak, my Sony ES HU is 19W RMS and 50W peak. The real selling point for me is it's just a little time, wire, and soldering. I'm just brainstorming here, and just shooting for better, not spectacular. I'd love a new HU, MB Quart 3-ways up front being pushed by a quality amp, maybe a 10" sub in the back for a little kick, but I have way too damn many things to fix to even think about that. Talk amoungst yourselves...........

[Kristuphir]

I took a look at doing the "gutted amp" thing this weekend, and mine looked different than all the pictures floating around on how to do it. I couldn't really figure it out.

You probably already have, but if not, search AnthonyM5inCalgary's posts for some very informative talk on this...

[Tiger]

Factory amp is about 25W RMS... not peak... per channel. Head unit is 40W or 50W peak but about 25W RMS... so it is not worth the effort to convert. If you want to do it right... it is simply rewire the whole car like you said with external amp, etc.

No need to look for super high end speaker like MB Quart... As long as it is component set and priced right on ebay... that is it... Amp is the most critical and should be the one spent the most... not head unit... not speakers... what good is high end speaker if your amp cannot put it to use?

Old amps ADS or PPI are the goodies... McIntosh is awesome but too pricy even used.... they are too big too.

[onewhippedpuppy]

Thanks Tiger, it would be pointless then. I did a search earlier and saw somewhere that the factory amp was only 14W peak. I was just brainstorming, I don't care enough to really spend much on it. Lots of more important stuff to spend my little money on.

I used to have a PPI amp years ago, it was a whopping 50x2. I had it bridged, then wired in parallel to a couple of Polk Db 10s in a custom box, with a 1F capacitor. I always figured I'd kill it, but it just kept going. On a hot day if we had the stereo cranked and the car not moving it would sometimes overheat, it ran so damn hot you could drip water on the top and it would boil instantly!:D

[onewhippedpuppy]

Anybody have any more info on the factory amp? What would it take for the factory speakers to sound better, 50W RMS?

[Derek A.]

I have 100w 2x going to the front 6 speakers and 65w 2x going to the rear 4 speakers. Then 250w going to the 10" sub. I would try and find at least 50w 4x or 75 4x. Then maybe look at a powered bazooka tube.

[NovceGuru]

Damn I wish I would of thought/known of the gutting idea before I hacked out the factory amp and cross referenced the wire colors/grounds etc with my alpine...eliminating the crossover, damn damn damn! This summer I might rewire with some infinity kappa's..mmmm treble!

NovceGuru

[genphreak]

Damn I wish I would of thought/known of the gutting idea before I hacked out the factory amp and cross referenced the wire colors/grounds etc with my alpine...eliminating the crossover, damn damn damn! This summer I might rewire with some infinity kappa's..mmmm treble! NovceGuruYea, using the stock cross-over / EQ module retains the quality of the custom sound system and dumps the old-tech booster amp BMW managed to specify as OE. I don't know why BMW ever did this, the clarity and low distortion of a line-level head unit driven by a decent amp is just soooo superior and is no an additonal cost.

I run what my amplifier claims to be 80W rms into each channel, though I do not drive it anywhere near that high- the factory speaker setup is probably rated at 10-20W rms per channel. I followed good previous advice and filter all low level (sub 100Hz) sound out of the factory system using a crossover as I also run a 300W sub which covers this better; replacing the bass that BMW forgot to cater for. Maybe 80s music had no bass :D I dunno, never listened to it anwyay... However the mids and treble are so smooth I would have trouble getting anything else to sounds as good so this is the best of both worlds. A symphony sounds clean and distinct, club music is clean, punchy and powerful and everything in between is fine. The top end is not coloured, there are no metallic tingles as put out by cheap mids and tweeters, or inperfect placement. My ear is pretty good- I'm not a doof doof head. A well-recorded quartet duds almost every car system I've heard, but this keeps it together remarkably and I'm rapt.

However, it is possible to blow the factory system so it is not a show stopper. Sounds damn good enough in the car for me though and would damage my hearing if any louder.

The amplification is way OTT of course but it is what came at the price. With the system running with a flat equlization the sound is nothing short of terrific. I would reccommend everyone to gut their amps and run new line-level wires down to the back from their headunits.

As it sounds so good flat, and the fader in the dash still works, if I were to do it again I would do it the easy way and avoid line level cabling through the cabin and rear seat (as this is really not easy to do nicely):

ie Use the headunit's current speaker wires (blue and yellow) and intercept them where they feed the factory amp in the trunk: Run them instead to a pair of Male RCA plugs for input to your amplifiers (you need 4-channels of course, or 5 if you want a sub as well). Whilst you are at it you also need to intercept the white wire (pink trace) from the factory crossover network connector so your new boot-mounted amps will turn on with the stereo.

If running a sub get a passive crossover unit mounted in the boot you can split sound to your amps and make any adjustments to the sub. You do not need to tho, the wires you have just tapped can be split to 4 RCAs and will drive 4 channels as well as they drive 2.

Some eqs have crossovers (or low pass filters) which stop the low frequency stuff going to the front and rear amps so may be used instead of a crossover... having an eq up-front just takes up glovebox space as the system is so well balanced you really don't have to worry about adjustments- not even on the head unit!

Once all this is wired you just run the 4 speaker outputs from your amps to factory amp (which you have to remove the booster circuit from, rendering it a crossover network). You simply wire in the output wires from your amps , just have to be smart with your soldering or risk blowing an amplifier)

I even used the remote on relay in my crossover network to drive the relays in my amps jic my headunit objected to turning on 3 devices on its own through the little pink wire previously mentioned.

:) Nick

[Anthony (M5 in Calgary)]

... so it is not worth the effort to convert. If you want to do it right... it is simply rewire the whole car like you said with external amp, etc.



The factory booster amp is 20W per channel at 4 ohm. Here's a datasheet:

http://www.st.com/stonline/products/literature/ds/1451/tda2005.htm

It's a nice chip amplifier but totally outclassed by more modern amps in newer head units such as the Sony. The major failing in the original setup is that the head unit drives the booster with speaker level signals and that adds a lot of noise. Nevermind that the factory HU has poor quality output to start with, then amplify it... great.

The system will sound much better using the outputs from the head unit, wired directly to the crossover input - well worth the effort IMHO. I had this configuration at one stage and it sounded far better than stock but revealed the low frequency limitations of the factory speakers (40W rated woofers BTW). The factory speakers are very good and have butyl surrounds not foam - I would only change them if I had big $$ to spend.

The factory speaker wiring is excellent - twisted pairs for every speaker. I wouldn't change it either.

Also, removing the booster amp's "guts" (the power amp block) eliminates the equalizer module's functionality as it is driven by the factory head unit.

Run the speaker wires down the driver's side just inside the doors. Once you pull back the carpet from the door sills you can push the wires way down into the floor padding - it's about 4" thick. This way the wires are well clear of other wiring that could cause interference. Cross factory wiring harnesses at right angles to further reduce noise.

Experiment away - great fun, small $$.

[onewhippedpuppy]

Thanks Anthony. So you think it would be worth my time to run 4 sets of wires from the HU to the crossover and solder them in? Does the booster stage just unplug?

[onewhippedpuppy]

Nevermind, I re-read an old post of yours. Totally reversible, I think I'll give it a shot this weekend. Anything special I should use solder-wise or anything?

[Incantation]

i think it's really a matter of how much you want to spend. if you're short on cash or don't want to buy some good stuff.. projects like this might make sense. they can be fun too.. but if the goal is better audio in the cabin you'll want to start swapping out everything

[onewhippedpuppy]

How much do I want to spend? $0.00.:D I don't care all that much, but if I can improve my stereo for just a little time and wire, I'm all for it.

[Anthony (M5 in Calgary)]

Nevermind, I re-read an old post of yours. Totally reversible, I think I'll give it a shot this weekend. Anything special I should use solder-wise or anything?

Nothing special about the solder, just use electronics grade stuff and watch out for shorts.

Have fun.

[onewhippedpuppy]

Is there any connector sold that I can put the wires into, then fit them over the prongs on the board? I haven't soldered for years, not sure how confident I am in my skills.

[genphreak]

Is there any connector sold that I can put the wires into, then fit them over the prongs on the board? I haven't soldered for years, not sure how confident I am in my skills.No, they are unique AFAIK. RadioSpares or DigiKey may, but finding it would be hard and you would have to solder the connector anyway. I'll post a pic this weekend that shows the connections more clearly than the previous ones.

A piece of advice, forget the amp in your head unit for 2 reasons-

1) A separate amp will sound much better than ANY head unit ever could (head units have cheap, low performance ICs, not chunky output stage designs like separate amps that have a chance of dissipating heat let alon have space to do things in). The power cable (and the size) is the key here- an amp usually employs a 20-40A fuse, head units are never bigger than 15A)
2) A separate amp is dirt cheap
3) running 4 speaker wires will be a PITA.

You can use the current feed wires for line level or high level jic you are not sure. Be sure to read my rpevious post, it describes the lot.

:) Nick