factory amp bypass (my way - lots of pics)

[filmy540i/6]

This thread is a very interesting read. Not that I would try to bypass any of the stock components on my own, but I'm sure there have been myriad upgrades to our audio systems since my '95 was built and I need some improvement.

Do any of you stereo gurus have a link that explains what all of these components do (HU, amp, crossovers, etc)? I'm talking generalities, not BMW-specific. I would love to have a better understanding of what's involved when I upgrade my HU.

Great post, OP!

[tim eh?]

This thread is a very interesting read. Not that I would try to bypass any of the stock components on my own, but I'm sure there have been myriad upgrades to our audio systems since my '95 was built and I need some improvement.

Do any of you stereo gurus have a link that explains what all of these components do (HU, amp, crossovers, etc)? I'm talking generalities, not BMW-specific. I would love to have a better understanding of what's involved when I upgrade my HU.

Great post, OP!

Thanks! Upgrading the head unit a bit problematic because of the e34's design. (I'm no guru though, I just know a bit about acoustics)

Sorry I don't have any links except maybe here are some good examples of what people do.
http://www.diymobileaudio.com/forum/diyma-build-logs/

But, ahem, in a nutshell, in the e34 the head unit is just a signal selector (ie. cd/radio/etc) and sends 4 (FrontRight, RearRight, FL, RL) low current signals to the amp in the trunk. The amp boosts each of these signals to a level that will 'drive' the speakers (which basically work like resistors except instead of creating heat they move the cones in and out which is what makes the soundwaves). The amp sends this signal through the crossovers which split the signal up so that the low bass goes (for example) to the big speaker in the footwell, the 'mids' to the dashboard and the high stuff (eg the tsst tsst of the highhat) to the tweeter in the door. This is necessary because sound waves vary greatly in size, which is why the speaker placement is important too. The waves that make the 'tsst tsst' sound have a wavelength of a pinhead, but low bass waves are bigger than your head, so you can try and make one speaker play them all but it won't be as efficient, and will invariably lose out on both extremes when you boost the volume a bit. The 'component speakers' in typical home and car audio systems are made up of 2 or more speakers and the speakers have the crossovers built into them. The 'speaker ground' completes the circuit back to the amp.

But in the e34 the crossovers are inside the factory amp. Which is a pain, because the amplifier is the weak link in the factory system... it's just weak is all, if you want to improve the sound it is the first thing that has to be replaced. Pretty much all of the typical head units sold in stores have an amplifier built into them so you can just get anything that has a 4x?0W output and it will be an improvement, but if you just connect it to where the factory head was then it runs through the weaker (4x+/-15W?)factory amp before going to the speakers, which really kills the sound. But it's the only way to use the factory speakers without doing a bypass. Normally you should be able to do what's in the photo below but for some reason as I mentioned this didn't work for me.



I don't know if any of that makes sense, but that's my understanding of it anyway fwiw. It's a bit more complicated than your average car. When I bought it the (aftermarket) head didn't work and I though 'no problem, I can do car stereos easy' but it turned out to be a real bitch and it took me forever to get it working. I don't know, this kind of technology hasn't changed much since '95, and unless something breaks or you need to hook up an ipod or something I wouldn't mess with it... I never heard a stock e34 system actually, I imagine they sound pretty decent even with the feeble amp.

[repenttokyo]

how bad do standard head units sound when plugged directly in? Is it 'worse' than the factory head?

[repenttokyo]

Ah - just saw that you have never heard the factory system.

[tim eh?]

He himself said "none"

that is the meaning of DIRECT.



BMG: those panasonics are anything but clean, and you had a grand total of 15 clean watts to them. they are bright though!!!

I'm going to push the hell out of the Nokias with an active setup, then I'll start swapping drivers for home theater stuff (peerless 2" domes are looking very nice right now) when they eventually blow. so far they have not... passive with 80w rms (or 200wx4 in headunit makebelieve ratings)

are you sad because you haven't blown your speakers yet? I wish I hadn't... there is one screw in the rear speaker assembly that is impossible to get at! I wish they were in the roof!

[tim eh?]

What do you mean though by standard... you mean stock or aftermarket? Now that I have heard the speakers properly I have a pretty good idea of what stock would sound like.

edit - oh i see what you mean - your average sony or whatever head unit would sound worse than the stock unit when running through the factory amp. if the new head unit has line level outs (ie rca) you could run those and might see a small improvement over the factory head but the main problem in the factory system is the amp. 'amping' the amp makes it worse. I think Derek A.'s head is a factory head if I understand it.

[Derek A.]

My head units is a blaupunkt unit - that no longer uses the speaker level outs:


I have an rca that runs to the trunk and feeds en electronic crossover:


Which in turn feeds three amps - one for the front 6 speakers, one for the rear 4 speakers and one for the sub.

Here is the diagram I used for the amp wiring:


Here is a shot of the factory amp section removed from the enclosure:


The system really sounds great - I am very happy for the minimal investment. Nothing to from an engineering perspective.

[tim eh?]

That looks great, I wish I could afford to give up some trunkspace.

Where (hz) do you crossover to the sub Derek?

I'm trying to figure it out, I want to use an 8 ohm speaker... does that double or half the frequency of a 4ohm crossover? anybody know?

*- ok i figured it out - on a low pass filter, the cutoff frequency with an 8 ohm speaker will be half of one with a 4 ohm speaker, ie 200hz @ 4 ohm = 100hz @ 8ohm.

**- check it ... soon...


***- and to clarify... upgrading just the head is fine just be sure to get a unit with line outs and use those instead of the speaker outs, although it will still work using the speaker outs just not sound so good.

[Derek A.]

Not really sure what the crossover point is. I basically did it by ear.

[BMWDriver]

I see wires soldered to the crossover board, but what are they connected to at the other end ? I'm starting to guess the speaker terminals of the amp box. What gauge ?

And Tim, I see black and blue wires on Derek's pic, were they missing in yours or are they already there ?

I'll soon be opening my amp later this week or this weekend.