95 530i Aftermarket Stereo

[Anthony (M5 in Calgary)]

if ur using a 4 output stereo u will need to cross the 2 commons together ... example: front left and rear left has 1 common sometimes they provide 4 wires so u need to cross the 2 commons to the amplifier input common, the same for the right. the amplifer used in BMW has low impedence input so u dont need to worry about the distortion unless the stereo u bought has more power than the BMW amp.
BMW amp uses the TDA2005 IC ... its a 10W X 2 or 18W BTL ( Mono Bridged ) I remember that it had 4 ICs inside ... with a passive crossover for the tweeters ... so this is powerfull enough ... some stereos has power upto 25W X 4 but that's not so real. BMW amp is close the the max power that can be delivered from 12V power supply. if u want more then u need to install an Amp with PWM power supply and that would be a different stroy.
if u had a problem I can draw u a simple wiring schematic for ur system ... I have the same setup with 2 more high power amplifers.

The factory wiring between the HU and the amp may well have common grounds. I just ditched the whole problem by running leads directly from the new HU to the inputs to the factory crossover, amp block removed. All of the outputs from the crossover to the speakers are separate and isolated from ground.

Feeding the low impedance inputs to the factory amp from a higher power HU completely defeats the purpose of any HU upgrade unless all you want is the added technical functionality of the newer unit (MP3, CD, whatever).

The TDA 2005s in the factory amp may well be configured BTL and give a theoretical 18W/ch but they still sound like crap. Having gone through numerous configurations all keeping the factory speakers, my final config sounds by far the best of all of them.

BTW, modern audio amplifiers achieve high output power by using switch mode power supplies to increase the 12V available in the car to a +/- 35 or more giving 70V+ swing for the amp. Also, class D amps can drive very high outputs using low voltage. I've seen 20W from a 3.3V supply.

HTH,
Anthony

[Mobius]

Also, class D amps can drive very high outputs using low voltage. I've seen 20W from a 3.3V supply.

So, what are the drawbacks of a Class D amp?

[TheDuke]

Are you able to use all of the speakers in the vehicle. Because I know that ....

I used harnesses to connect the radio, didn’t have time to play around with wire matching (or too lazy. All speakers work. It's true the radio has enough power to blow the shi&$ out of factory speakers.

[grave77]

thats true.. I suggested my way for quick installation, I'm cosidering ur methode for installing a DSP rack. I have 4 outputs and I need a hi-imp. inputs ... TDA2005 has been there for around 20 years or more ... there are new versions now of TDA power ICs ... I have 4 or 5 Datasheets of them if ur interested. Class D is the ultimate power amplifiers power wise, but 20W with 3.3v is impossible ... P = (V^2) / R so if the speakers were 2 Ohms and the amp slews to max supply voltage then the output power will be approximatly 16/2 = 8 Watts RMS P.M.P.O output is crap ... sometimes they mutiply the RMS by 35 to write down fictional power outputs. ( pocket radio delivers 1W RMS max,on the front written 35Watts.

[Anthony (M5 in Calgary)]

So, what are the drawbacks of a Class D amp?

None. Just new technology, the output looks nothing like the old fashioned analog signal you may have ever seen on an oscilloscope. Very efficient.

Anthony

[Anthony (M5 in Calgary)]

thats true.. I suggested my way for quick installation, I'm cosidering ur methode for installing a DSP rack. I have 4 outputs and I need a hi-imp. inputs ... TDA2005 has been there for around 20 years or more ... there are new versions now of TDA power ICs ... I have 4 or 5 Datasheets of them if ur interested. Class D is the ultimate power amplifiers power wise, but 20W with 3.3v is impossible ... P = (V^2) / R so if the speakers were 2 Ohms and the amp slews to max supply voltage then the output power will be approximatly 16/2 = 8 Watts RMS P.M.P.O output is crap ... sometimes they mutiply the RMS by 35 to write down fictional power outputs. ( pocket radio delivers 1W RMS max,on the front written 35Watts.

Amplifier hype aside, the best way to drive the factory speakers is by bypassing the interface between the factory HU and the factory amp then just connecting the inputs to the crossover terminals.

Combined with a 5 channel amp driving only 80Hz and up to the factory speakers and adding a sub the sound is as good as you'll get with high end systems in new cars. The factory 5.25" mids can easily handle high SPLs once the bass elements are removed.

HTH,
Anthony

[grave77]

thats true ... I'm using them as midrange now ... I just wonder if there is a high impedence input ready made for the amp or not. I didn't really check it closly yet. I would be glad if u know the pins

[Mobius]

None. Just new technology, the output looks nothing like the old fashioned analog signal you may have ever seen on an oscilloscope. Very efficient.

Ah. I just keep hearing about how great Class D amps are; I figured there had to be some downside.

[saj3n]

The factory wiring between the HU and the amp may well have common grounds. I just ditched the whole problem by running leads directly from the new HU to the inputs to the factory crossover, amp block removed. All of the outputs from the crossover to the speakers are separate and isolated from ground.

Feeding the low impedance inputs to the factory amp from a higher power HU completely defeats the purpose of any HU upgrade unless all you want is the added technical functionality of the newer unit (MP3, CD, whatever).

The TDA 2005s in the factory amp may well be configured BTL and give a theoretical 18W/ch but they still sound like crap. Having gone through numerous configurations all keeping the factory speakers, my final config sounds by far the best of all of them.

BTW, modern audio amplifiers achieve high output power by using switch mode power supplies to increase the 12V available in the car to a +/- 35 or more giving 70V+ swing for the amp. Also, class D amps can drive very high outputs using low voltage. I've seen 20W from a 3.3V supply.

HTH,
Anthony

Thanks for all the help Anthony, and everyone else too! Very useful information. My Wire harness arrives today and I will be doing the installation tonight. I will post updates as soon as I finish the work.

Thanks again!

[Anthony (M5 in Calgary)]

thats true ... I'm using them as midrange now ... I just wonder if there is a high impedence input ready made for the amp or not. I didn't really check it closly yet. I would be glad if u know the pins

...and drive the OE booster amp? There's no such input on that amp but I bet it would be no trick to re-jig the input sensitivity of the TDA2005 circuit though. Usually low Z amp inputs just use a moderately high power (say 1-2W rated resistors) load around 70 ohms to provide stability for the amp that's driving. The circuit should be easy to mod but I suspect the load resistors are on the main portion of the amp board, not on the power module.

I suspect BMW's reason for going the booster method was to allow for a base HU that would work for base applications and added the booster for "higher market" cars. Plus, speaker level signals are more immune to electrical noise.

HTH,
Anthony