john banks

It is funny how setups come back to haunt you. Pug install (original factory headunit!) with 2 channel amp at 2 ohms running front 6.5" comps and rear 6x9 through 1 ohm resistor really was sounding quite pleasing. The speaker outputs from the headunit go through a line level converter to an RCA lead which runs up the centre console towards the boot away from the power lead. The converter really helped to reduce alternator whine - no further reduction by using common ground connection for headunit and amp.

Then - this morning I put some jazz and classical in the changer and it sounded really nice. Then on a quiet piece I got alternator whine - that INCREASED in volume as the headunit volume was increased. Now I reckon that this is not a ground loop and is noise that has got into the signal at the headunit. Now I can put up with it if this is the best I can get from the factory unit as it is not terrible, but I wondered if a noise isolator on the headunit power supply might help. This car is full of motors and I think they all add their bit of noise. Any ideas/experience of similar? Thanks.

ScoobyDoo555

Hey John

Sounds like a dodgy RCA lead to me..... had the same problem in my old Pug too.....

Unles you've already tried this, hope it helps


Dan

john banks

Thanks Dan have just tried a different RCA lead - and unfortunately it makes no difference - neither does the route it gets thrown via to the back of the car. What about a power supply noise suppressor?

john banks

Top.

ScoobyDoo555

Hmmm......

My m8 has a Saab Turbo - had the same problem. I positive he got round the problem using the PSU noise suppressor you mentioned.....

However, I'm not 100%.....

I'll ask him tonight.

Dan

kryten

john, i would assume its a combination of the head unit and amplifying a signal that wasn't meant to be!

this sounds more like noise - does it happen with the engine off?? (ie no altenator!)

some time back, I tried doing some major modificatios to a factory unit, including bypassing the outputs and taking line level off the ciruit board. there was noticeable noise when I used outboard poweramps that was just inherent in the unit.

if it increases with the volume of the headunit then the noise must be present before the pre-amp in which case I doubt there's a lot you can do.

adding amps reveals things that aren't noticed with internal amps - i even found that on one of my old pioneer units, when on max volume and playing a zero bits (ie totally blank) cd the RADIO signal could be heard!!!!

john banks

No it is not present with engine off. It is present on quiet bits with volume high, varies with revs, louder at high revs and louder with more electrical equipment on which is why I thought it was alternator. But it does vary with volume and is not present when headunit is at very low volume.

Eagerly await reply re Saab Turbo and filter Dan - thanks.

Another thought Kryten - re your mods to the headunit - the CD changer sits right next to the amp. On some CD changers I have seen phono sockets for the audio - sadly not on mine. But even if I could link it electrically using the headunit only to control it, I would need a separate volume control up front and it would be messy. Nice thought though to avoid run of wire to headunit, corruption through headunit pre/power amp and then RCA converter and lead to back of car and cut out all the "middlemen"?

[This message has been edited by john banks (edited 20 June 2001).]

john banks

Power supply noise suppressor fitted to good effect - thanks all. No alternator noise now even with electric everything on and 6000rpm with headunit on max volume playing cool jazz. Back to the thrash now I know it is noise free Better still, back to the Scoob now it is all finished.

kryten

Glad its fixed john, though it sounds more like a noise picked up by the power supply was causing interference.

Had a similar problem on a mondeo - due to location of an amp, it picked up 'clicks' from some of the ECU boxes. Rerouting cables and moving the amp cured it.