E30 Audio Overhaul - My Project Details

[StereoInstaller1]

Wow, that sounds FUN....hopefully you aren't claustrophobic! I suppose that people of that sort aren't attracted to this line of work though.

Generally, installers are smaller than me. I am about 270, 6', 52" chest, 19 1/2" neck...I don't fit well.

[bmwman91]

thus I have been cranky for many many years.

You should have seen my burly self shoved between the hull and passageway in a big ass MasterCraft the past 2 days, wiring 3 amps while laying on my back, reaching over my head, in record breaking heat.

BIG fun there...thank god the damn boat sounds good.

Wow, that sounds FUN....hopefully you aren't claustrophobic! I suppose that people of that sort aren't attracted to this line of work though.

[StereoInstaller1]

Getting in & out of my trunk 100 times in the hot hot weather made me a bit cranky.

thus I have been cranky for many many years.

You should have seen my burly self shoved between the hull and passageway in a big ass MasterCraft the past 2 days, wiring 3 amps while laying on my back, reaching over my head, in record breaking heat.

BIG fun there...thank god the damn boat sounds good.

[bmwman91]

OK I have regained some of my composure lol. Getting in & out of my trunk 100 times in the hot hot weather made me a bit cranky.

I have verified that the alternator/ignition whine is coming from the HU/signal lines running to the trunk, not the 6XS or amp. This was done by simply unplugging the inputs to the 6XS & powering it all on...no more whine (although there is a faint high pitched buzzing that is likely from speaker lines running right next to the amp power line...gotta move that!).

I have an LC6i on the way. This will enable me to use the pair of balanced signal lines for each channel, rather than just one. Using the signal+inverted signal allows for common signal rejection (since the lines are physically close together, the same noise is induced in each, and the LC6i will reject any common signal between the 2 lines, basic opamp stuff really).

As for the skipping CD43...that makes me mad lol. I will pull it & do a thorough physical inspection as well as asking around for others' experiences. I will either buy another one & replace this one (that did fall off of the roof of my car once so it is reasonable to assume I broke it), or go aftermarket with something VERY conservative.

Oh and the system sounds f'ing amazing with the car turned off lol. It brings a smile to my face...sounds better than any factory premium sound package I have ever heard in a car!

[george graves]

Sell the car you just put that much work into? Are you kidding me? Wow. Well - can't wait to see the end results. Looking forward to some pics!

[bmwman91]

Well, I am done, sort of. I will post pics another day, I am hot, tired & annoyed.

The system sounds great, on-par with my home one...when the car is off. The biggest problem with the setup now is alternator/ignition whine. This is most likely because I am running single-ended outputs all the way across the car to the 6XS. I am optimistic that buying a level converter that takes both outputs (signal & inverted signal) will reject this crap.

The other issue has to do with the CD player, but that is a separate thread.

Shit. I was hoping to be done with this lol. I think I want to sell the car & buy a nice new one with a warranty that I will never touch. I think I am officially over projects.

[rooster]

fix my broken amp!!!!!




wow interesting so lost though

[reelop19]

If you need an amp to work on I have a 4 channel of which only 1 channel works. Let me know if you'll fix it for me

[BeirBrennerE30]

yeah this is crazy. I really need to brush up on my audio/amplifier design. This is just straight awesome.

[M42Power]

I love this thread. I always felt that the good stereo was ment to be left at home to play vinyls and the e30 was hopeless. But now there is some real sound system going in! I am gonna need to overhaul mine.

[bmwman91]

I feel like I'm in Physics class again. Very interested, but lost in trying to wrap my head around what I'm reading! This thread ROCKS!

John

What the fuck is going on!!!!!!!!!!!!!!!!!

My head hurts.
But I'm lovin' this thread.

Haha don't worry too much about it. This stuff is all totally excessive & there's no way I will hear a difference when driving on the highway. It's more "practice" for when I do my next home audio build...building some of those monster double horns AND my own amps. One of the virtues of DIY audio is being able to totally overbuild everything beyond reason. It's good experience...audio touches on all sorts of mechanical & electrical engineering principles. It's also a ton of fun to build & mod things (which I think is very much in the spirit of the E30 lifestyle)!

[dirtysix]

My head hurts.
But I'm lovin' this thread.

[Danny]

What the fuck is going on!!!!!!!!!!!!!!!!!

[harv]

I feel like I'm in Physics class again. Very interested, but lost in trying to wrap my head around what I'm reading! This thread ROCKS!

John

[bmwman91]

Update time:

I think I am done with the amp mods for now. There is one nagging issue left, but that will probably take more time than it is worth. I'll explain at the end of the post.

To start, I wanted to bypass the CH5 crossover so that the nice Audio Control unit I bought could handle that. Crossing over at 220Hz is maybe a little uncommon, but I want to give it a shot since simulations look promising with this crossover frequency. I also like to try to distribute the acoustic energy in decades to reduce distortion in the drivers from nonlinear excursion.

I traced out the input stage with a DMM. Painstaking work...4 layer boards are a pain.


After some jumping & rearranging a resistor...


While I was in there, I replaced the opamps with some true audio-grade ones. The stock ones are MC4558's. Their replacements are OPA2134's which are well regarded for their performance characteristics while still being of a reasonable price.


I replaced 7 total. All you need is some desoldering braid, tweezers & a soldering iron with a needle tip.



The other big project was getting the gains matched & locked in for all of the channels. I don't trust cheap potentiometers because a)vibration makes them shift value, and b)double pots are notorious for having poorly matched resistances (gains varied 8% between CH3 & CH4 with the stock pot). So, I got out my trusty scope & signal generator & did this for all channels. After giving myself a little margin to avoid clipping (outputs generally don't get ALL the way to the rails) I removed the pots & installed some resistors. Yeah, it is sort of ugly, but it is how you get exact odd-ball values.

The gains were set to provide maximum unclipped output with the maximum input signal (13.5V peak) received from the 6XS.



Crazy resistor mishmash goodness!


I was glad to be done with all 5 channels. What a pain!


Just one more close-up of some mods. I did not replace ALL of the opamps since the ones related to the crossovers aren't getting used at all. Maybe if I go & sell this someday I will replace them all if the buyer doesn't want to use an external XO. Spot the "better" ones!


So I had mentioned one annoyance at the start of the post. Well, channels 1, 3 & 4 are perfectly matched. For a given input, they are within 10mV of each other. For some reason though, CH2 behaves differently. The gain in the power stage must be a bit higher than the others, and maybe its biasing is tweaked (probably due to tolerances stacking in cheap components). Its output can be up to 2-3V higher than the other channels at high outputs for the same input, and it clips 3-4V higher (it goes ALL the way to the rails while the others don't). I spent some time with a DMM trying to map out the stage, but it is too much work since I cannot remove that board from the case to see the bottom traces (I could, but I would mess up the transistors' heat sinking). It is probably just a bias resistor that it out of whack. Still, the difference is really only prevalent with really high outputs and I don't plan to operate there much anyway. It might be time to leave well-enough alone!