odd problem with sound system

[courior]

Hi all.

Current setup i have is as follows... I have a Pioneer head unit feeding 2 normal car speakers in the footwell (this on its own works great) ... But i wanted some rear speakers and a bit of bass so i got an old but powerful 2.1 computer sound system and removed the transformer and wired it up to take 12V. Mounted it all in the car and when i plug my phone/mp3 player to the input jack (that would usually go onto the pc) it sounds perfect!

Problem comes when i attach the input on the 2.1 system to the RCA PRE-AMP output on the head unit. When its at low volume the 2.1 speakers hiss and pop randomly... but when i crank it up it sounds great! (ok so workaround is to always have it at 100% volume, but thats not practical is it ) ... What could be causing this? my immediate thought was that i got the + and - mixed up from the 2.1 sound system, but then surely it would hiss and pop with no input or a low input from my phone also?

There is no special settings on the head unit i can find, and i have plugged it into the FRONT pre amp out not the sub output. Any ICE experts have any ideas?

Cheers,

Courior

[Anton]

Maybe it's picking up electric noise from the SJ's electrics via the ground on the speaker input/pre-amp out?

Wire up headphones to that output and see if you get the same problem.

[Edweird]

I agree, it could be ignition noise. You might need to put a hefty capacitor across the system's power supply.

[courior]

Forgot to add. This is with no ignition. Just the key in the acc position. And also happens with the motor started. I've been reading and I think its to do with the voltages supplied by the headunit over the pre amp out.

[Edweird]

Okay, scratch what I said. it sound like it's a gain issue then. not sure if you can but is there some way of reducing the gain on the 2.1 system and increasing in on the preamp?

[dan_2k_uk]

Don't think I've ever seen any options to do with preouts on any head units I've ever had. Easy quick solution if you only ever listen to music from your phone would be to use a splitter to connect the phone jack to both at the same time. No good if you wanted radio or CD though.