[EffectOne]

Hi all,

My 2007 E92 had the base stereo system. I have recently upgraded as follows:

- Xtrons PE9690BPL head unit (front L/R RCA, rear L/R RCA + mono sub RCA);
- MB Quart QM200 (2x subwoofers, 2x midwoofer door component speakers, 2x tweeters);
- MB Quart QM100 (2x rear panel speakers); and
- Pioneer GM-D8604 amplifier.

Being my first audio upgrade/install of any kind, it took me and a mate about 8 hours to install, including lots of question marks over wiring loom locations, etc...

I have attached a diagram showing how it is wired up (apologies for the crudeness). You can see that the front/left RCA pair is connected to channel A on the amp normally. The sub output from the head unit is a mono RCA out, which is connected to the red input only on channel B. The channel A left and right speaker outputs are connected to a crossover in each door, which then runs separate cables to each midwoofer and tweeter. Speaker cables are run from the left and right on channel B to their appropriate subwoofers directly. The upgraded rear speakers are left running on the canbus, using the old speaker connections. The amplifier is properly powered and grounded.

The Problem

The left subwoofer isn't firing at all. This will probably seem obvious to some of you, given that it is a mono RCA sub output going into the amp (we assumed the amp would duplicate the single incoming signal across both outputs). To rule out component damage, we have hooked up each subwoofer individually to L and R on both channels A and B, and got sound from them on every channel. So there appears to be no damage to either the left subwoofer or the amplifier which could be the cause of the problem.

We next tried plugging a y-splitter into the mono RCA output from the head unit, and running both red and white RCA cables into the channel B input on the amp. That had no effect and the left subwoofer was still 'dead' (which surprised us!).

Does anyone have any suggestions on what I could do to get both subwoofers firing? The obvious answer is to use the unused rear L/R RCA outputs on the head unit to connect to channel B, instead of the mono sub output. However, if I do that, I will lose the ability to control bass levels in isolation in the EQ menu on the head unit (a separate 'sub' slider controls the sub output in isolation to the rest of the RCA outputs). Also, if I solve the problem by doing that, I won't be able to add a second 2 channel amp to the setup in future to power the rear speakers (I don't want to leave them plugged in through the canbus/quadlock connection forever).

Thank you, and apologies for length of post!