bena3t

hey guys i got a 99 A3T with a few mods (APR Stage 1, 18" RS4s, GFB BOV, FK sport suspension, N75J, etc etc) and have had a custom stereo which changes quite regularly since the factory head unit needed to be replaced for the 3rd time (4 months out of warranty and they werent interested)...the car came with bose concert premium, so i havent touched the speakers...
ive got a blaupunkt acapulco mp52 (which has been nothing but trouble since i got it), a kenwood KAC628 powering the fronts, a kicker KX.600.5 bridged powering two Pioneer TS-W255C 10" subs...

im getting engine noise through the front speakers....
ive run the power and rcas on either sides
ive checked its not the amp by swithing rcas between them
everything is grounded well, including the HU which takes the OEM grounding and radio

before i go pulling out the damn dash (again) i was just wondering if it could be the converter from the rear of the HeadUnit into rca leads...
i read a thread on page 6 i think where MAC SUB said
"Line level converters are nothing but trouble especially on Bose systems, as the Bose output is expecting a 2 ohm load, line level converters present a 4 ohm load so you get a very faint RCA signal"
is this what you mean?
if so is it probable this is my problem?
that would be great cheers!!!

MacSub

You've got a blaupunkt acapulco mp52. Surely this has RCA outputs to the amp driving the fronts? So you shouldn't be using any line level converters.

Line level converters take the speaker output (already amplified) back down to a low level suitable for feeding a power amp. They should only be used when the HU has no pre-outs (RCA outputs).
They are a problem because they introduce noise and distortion because you have one amp feeding another.
You should definatley upgrade the front speakers if they are running off a Kenwood amp. The Bose speakers are 2 ohm impedance, so make sure the Kenwood amp is running in 2 ohm mode (if it is capable), otherwise the low impedance speakers will be overloading the Kenwood amp.
Are you using the rears?
The Bose setup has a 4 channel Bose amp which drives all the cabin speakers, is this being used or have you bypassed it?
None of the above should introduce engine whine unless you are using the line level converter.
Are you using any of the Audi wiring (apart from the ISO power plug)?
My first choice would be to add an additional thick, short earth lead to the chassis of the HU, don't rely on the Audi earth lead.
You could be getting interference back from the sub amp via the RCA's. If you unplug the sub amp RCA's is there any improvement? If so then you need to reground the amp as it is using part of the RCA screening to ground itself (ground loop).
Are the RCA's decent quality with metal plugs?
If you run the fronts off the sub amp (obviously with the lo pass filter off) do you still get the noise?

bena3t

yes, im running factory 2 Ohm speakers
Setup:
HeadUnit runs rears
Kicker runs 2 pioneer 10s at 300 each at 4Ohm Kenwood powers fronts at 75 each at 2Ohm

no, the blaupunkt DOES NOT have preamp RCA outputs...i need the crappy line level converter to run RCAs...the RCAs are high quality with gold connectors (round 60 australian a pop)...
ive just had to send the kicker away as its had issues, but ive decided to use this to power the interior speakers instead as it is capable of running at 2Ohm 150* 4...the kenwood is only capable of 75* 2 at 2ohm...its gone...im going to buy another 2 channel amp today that will power the subs...i will reground everything, including the head unit, but im pretty sure it must be the line level converter as i had the same setup running off the factory head unit....
ill let ya know how it goes
if i cant solve the problem ill rip out my mates head unit and try that(it has rca outs)
ive been itchin to get a decent head unit for a year...dont go Kaplunkt (ive sent it away twice for waranty work)
cheers
ben

MacSub

even the crappy Audi HU's have front & rear pre-outs.

bena3t

my audi head unit only had high level outs and so does the kaplunkt...im assuming the line level converter were talking about converts the high level outputs to RCAs...and THAT is where the problem lies...
maybe we got our wires crossed :P

MacSub

<center><img src="http://pictureposter.audiworld.com/66252/rca_adapter.jpg"></center><p>So you have to use a pre-out adapter to connect standard RCA's, like the one shown.
Yes the line level converter will be the source of the problem.

bena3t

cheers....just as i thought.....what can i do to get rid of this...i was speaking to a fella today who said u can get high quality converters that vastly reduce noise compared to the cheap on i got(when i got it i didnt realise that it a) was a cheap one and b) would have any effect on noise
cheers

MacSub

Ditch the HU, if it hasn't got pre-outs it must be the worst HU in the world. I can't think of any HU available in the last 10 years that doesn't have them.

Eddie3dfx

connector that you showed in the picture?
I want to split them into 4 channels
2 component fronts, rears, and 2 subs
is this possible?

howdeeaudi98

Ok..did you completely reroute the wiring from around the Amplifier or did you put the signal from your HU through it? The Concert has a suppressor circuit and maybe your AM/HU doesn't have a good enough quality suppressor to handle noise from a 12+ volt system. You hit about 15volts sometimes with older alternators (the guage reads to 16 at the max) and the ole alt may be aging it's companion voltage regulator, or your power leveling relay may be blitzing on you. Very odd how they do things at Audi, but..then again...