This is a crossover right?

[thatphysicsguy]

So I was digging through my dash tonight trying to install my new deck and I came across a duct tape-wrapped little circuit board with a couple inductors and a few capacitors.

I know the PO had Audio work done to the car but I'm not sure if I should trash this thing or not, my audio sounds okay without it albeit with a bit of interference.
Did the E30 come with a factory crossover that this replaced? or is this a puny little POS that I can scrap before installing my lukebox?

[phenobarb1]

It certainly looks like a crossover, albeit and incredibly poorly put together one. The factory premium sound setup sort of had a crossover to the tweeters, in the form of a capacitor mounted onto the woofer. So, the factory setup is a first order crossover, and this looks like a second order crossover, though I'm somewhat unclear as to how/why they wired it in like that. Do you know what sort of changes he made to the audio setup (different speakers, amp, headunit)? That could help clear things up. I really can't imagine leaving something like that to just dangle behind the dash.

[thatphysicsguy]

the PO had this work done in the 90s lol.

A new alarm, a new amp, and a new head unit were put in if that helps. the amp they put in looks very similar to the stock premium audio amp, too

[bmwman91]

Judging by the RCA connectors and transformers, I would say that it is a line level converter for taking speaker level signals and conditioning them for pre-amp level inputs to an amp. Those look like transformers rather than inductors. Unless you have an oscilloscope handy, I wouldn't bank on them being crossovers.

Warning: Nerd shit
The line level outputs from decks usually range from 0-13.8V (or whatever your battery is). When there is no output from the HU (say, on mute), both the + and - lines will be at about 6.9V (Vbatt/2) too since those amps operate in what is called a Bridge Tied Load configuration. You can run that signal through a capacitor in series to eliminate the 6.9V offset and end up with a -6.9V to +6.9V signal instead of 0-13.8V. However, pre-amp inputs generally tolerate -5V to +5V inputs or smaller. The transformers are there to cut the input signal down from 13.8V to (probably) 1/4 of that, so 3.95V or something.

[thatphysicsguy]

Judging by the RCA connectors and transformers, I would say that it is a line level converter for taking speaker level signals and conditioning them for pre-amp level inputs to an amp. Those look like transformers rather than inductors. Unless you have an oscilloscope handy, I wouldn't bank on them being crossovers.

Warning: Nerd shit
The line level outputs from decks usually range from 0-13.8V (or whatever your battery is). When there is no output from the HU (say, on mute), both the + and - lines will be at about 6.9V (Vbatt/2) too since those amps operate in what is called a Bridge Tied Load configuration. You can run that signal through a capacitor in series to eliminate the 6.9V offset and end up with a -6.9V to +6.9V signal instead of 0-13.8V. However, pre-amp inputs generally tolerate -5V to +5V inputs or smaller. The transformers are there to cut the input signal down from 13.8V to (probably) 1/4 of that, so 3.95V or something.

oh cool, today I learned. So now that this is out of the car, do I risk damaging the existing amp? or would sound quality just decrease...

I don't really care too much because a new one is going in on Friday, but it would be interesting to know.

[bmwman91]

Are you trying to run speaker level outputs to an amp's input? If so, you may damage it unless it specifically says that it is rated for speaker level voltages. There shouldn't be any change in sound quality, other than maybe if you end up clipping because the input level is too high.

[thatphysicsguy]

I haven't noticed any clipping so far. but I'm not blasting the music at all.

the amp is old and coming out anyway, so I'm not too worried.

[phenobarb1]

Yup, I think bmwman91 is probably correct about it being a line level converter. Never needed to use one myself, and got thrown by the odd setup. Always had the impression that such converters were bodge jobs, but maybe others have a different opinion.

[thatphysicsguy]

it seems sketchy yeah, and the work was done in the 90s, so methods were probably a bit different back then.