I have installed a 4 channel amp from the speaker out (high level) of the stock head unit of an R50 Cooper (Boost - CD53) to 4 new speakers.

The new speakers all work fine when connected direct to the head unit. When the amplifier is connected, the rear speakers work fine, but there is no sound from the front speakers.
Things I have tried:

• Checking and replacing all wiring from HU to amp
• Adjusting front and rear gains and crossovers on the amp
• Taking out the two inputs for the rears, just leaving the fronts connected to the amp - no sound
• Switching the rear speaker out from the head unit to the front inputs on the amp - front speakers worked fine with the rear input
• Connected a different head unit with RCA outs to the amp's RCA inputs and the whole system worked fine, but I want to use the stock head unit (no RCAs).

It seems like the front speaker outs from my head unit are not working, but they work fine when running the speakers directly. I also have a spare stock head unit and that behaves exactly the same.

The only part of the system I was not sure of was the high level input of the JVC amp only took the positive wires from each speaker out (ie FR+, FL+, RR+, RL+) and then a single black wire that attaches to "chassis ground". I spliced this wire into the ground coming out from the back of the head unit.

If I turn the system up full volume with just the front speaker outs connected to the amp, I get a little bit of sound crackling in and out very quietly.

I am stumped.
Any help would be appreciated.

 

Connect the front speaker ouput grounds to chassis ground?
Sit in the back?

 

Get a line output converter, that will change the speaker lines from the HU into RCA for the amp.

 

I considered this but the rear speaker output grounds are not connected to chassis ground and they work. Would this be a totally safe thing to try?

Yea
If worst comes to worst, I can hook the rear output up to the front inputs on the amp to get front speakers only, but I lose the bass from the 6x9s.

Could I split the rear output wires into wires for the front and back? (ie RR+ split into RR+ and FR+, RL+ split into RL+ and FL+) Could this overload the head unit? Are the rear outputs full range?

 

This was my next move if nothing else worked. I thought that the internal high input circuit of the amp would be a better solution. I am probably just going to get a cheap LOC to try. Are the cheap ones OK, or do they introduce noise and should I stick with name brands? I've never had to use a LOC before.

 

The cheap LOC worked. I now have the fronts running through the LOC into the amp's front RCAs and the rears running direct to the amp's rear high level inputs. The fronts have more volume, but this can be adjusted with the gains on the amp (or the fader on the head unit).

I would have run the rears through a LOC as well, but the shop only had one 2 channel LOC in stock and I wanted to get it finished today.

It would be good to find out what happened, but at least it's working...

Thanks chaps.

 

You should be able to adjust the levels on the LOC itself and balance the speakers.

Cheap LOC work well enough for most, but the expensive ones can clean the OEM signal, level the EQ (before applying it's own EQ), and prevent bass drop off and higher volumes. These units can cost hundreds but can make an OEM head unit rival the best of aftermarket units.