davestar

My system is up, thanks to a nice ground at the fuel pump. My install is pretty simple - i cut the pre-amp FR and FL signals and soldered female RCA jacks in place. I have two short RCA male-male "Y" adapters coming from the jacks, which connect to my long RCA pairs that run to the amp in the trunk. This allows me easy access to the RCA cables from the driver's seat so I can use an external audio source (protable CD player) for troubleshooting. The amp gains are set quite low - about 1/5 max. Unfortunately, I have a small but noticable amount of distortion. Here's my t-shooting so far:

(1) Car headunit, engine off, volume 0 ==> very very little background noise
(2) Car headunit, engine off, volume 20 ==> crackling/static during some passages
(3) Car headunit, engine on, volume 0 ==> background noise & alternator whine
(4) Car headunit, engine on, volume 20 ==> louder crackling/static during some passages (alternator whine inaudible b/c the music is purty damn loud)

(5) CD walkman, engine off, volume 0 ==> beautiful silence
(6) CD walkman, engine off, volume up on CD player ==> sounds perfect
(7) CD walkman, engine on, volume 0 ==> beautiful silence
(8) CD walkman, engine on, volume up on CD player ==> sounds perfect

Everything points to noise being picked up behind the center console. The fixes I'm considering are:

(1) Ground the head unit to the chasis to ensure the amp and head unit share the same ground.
(2) Shield the female RCA jacks. They're probably the most at-risk element back there, as far as I can tell.

Sound reasonable? I know elduderino did something similar, but doesn't have my noise problems. Thanks for any help.

elduderino

Good description, thanks!

1) If you lower the gains to minimum, do the noises go away?

2) When you hear the alternator whine, do you have hi-beam headlights/rear defrost on? If not, does it get worse?

3) Does the crackling come from the tweeters only or from other speakers also? (Are these factory tweeters? What equipment do you have?)

e_lectro

Are you testing with your cd walkman running on batteries, or plugged in to the car for power? If you are running off bateries, you elminiate a possible ground loop. So try it with it getting power from the car and see if the noise comes back.

Grounds could easily be the cause, the TSX seems very tempermental about them... I had to tighten up the bottom bolts on the cd player and move the trunk ground to get rid of my audio and video noise. (I moved the trunk ground to one of the bottom rear seat bolts.)

davestar

electro:

the CD walkman is running off batteries, so yeah, there's no ground loop problems in that setup. once i can get my hands on a cig adapter i'll be trying it off the car's power, but i don't expect a definitive answer from that either.

elduderino:

(1) when the gains are at minimum the distortion is still present
(2) the alternator noise is at a fairly consistent level, regardless of the added current draw of various accessories. revving causes a change in pitch obviously, but that's the only variation i can get.
(3) as far as i can tell, only the tweeters crackle. but as i mentioned, i can't get them to distort at all when running off a CD walkman, so i'm not driving them too hard.

my system is:

CDT HD-62s (fronts and tweeters)
Stock rear doors (powered off stock amp)
Removed 6x9s
Elemental Designs 10k sub
Aura 4150 (4x100) amp

elduderino

Thanks again. I would say for testing running the CD player off of battery is actually best, since you want it as a reference... and I would approach this as two seperate problems, attacking the distortion first. It's possible that your alternator noise will go away after the distortion problem is fixed, but either way, it's the more unusual and thus worrisome of the two, and I would attack that first.

This sounds like you are clipping the output of the deck... but there's no way that that should be happening at 20, as I know you know, I'm just thinkin' thru my fingers. My deck going into a JL 300/4 doesn't clip at 40 unless I have a CD with very high recorded levels. (My input gains are at minimum.)

Is there any possibility of there being a short in the connections at the factory amp wiring? Those wires are real short and real small, and I know I've been a bit paranoid myself when making up my connections. You can't meter across your RCA connections without disconnecting the amp and the head unit, and I wouldn't recommed going to that extreme yet...

Each channel has a (+), a (-), and a shield that is only grounded at the factory amp end for noise "drainage". By any chance could this (-) be either grounded or connected to the shield?

I would also try, just for science, temporarily unplugging the OE amp, just to see if the distortion changes. This is one of those deals where info gathering is really useful, but I don't always know what to test first (In a way, I miss t-shooting installations over the phone - it was intellectually challenging without the customer being mad at ME if I failed

Depending on the output impedance of the deck and the input impedance of the Aura, it's possible the deck doesn't like driving 4 channels of input on 2 channels of output. It's been done before (joerckt's Kicker 4-channel, for instance), but amps are different... so unplug the rear channels RCAs from the R channels of the Aura and see if it makes any difference in the distortion.

Also try each set of RCAs into the F channels of the amp to see if it makes any difference (another quick test that might or might not reveal useful info). This is more a test of your RCAs. Also bypass the "Y" adapters and run straight into the F channels.

Lastly, I would tap into the other set of channels from the head unit and see if THEY sound any better (with the OE amp unplugged). It's remotely possible that something bad happened to this set of op's from the head unit.

This applies more to the whine than the distortion, but where are the xovers mounted? The inductors in the xovers can pick up noise easily from power wires, electric motors, and ECU's, but it usually does not change volumes.

And in closing, with that level of system design and components, what in the world are you doing with rear fill? Drop that factory amp and those rear door speakers! It sounds like you have the potential for some good hifi if you get that crud outta the way

davestar

i electrical-taped the crap out of my soldering/splicing, so i really doubt that there's any shorts back there.

i've previously bypassed the Y adapters (sent only 2 channels to the Aura) and driven only the front speakers, but the noise remained.

my crossovers are mounted (or rather, are wedged) on either side of the OEM amp. i intend to pull them away from that noisy environment to see if that improves things. however if they're the problem, they should be picking up noise even when running off the CD walkman.

head unit ground and disconnecting the EOM amp seem like good options to try.

and about the rear fill - i considered bypassing the OEM amp completely, but the fader lets me cut out the rear speakers completely if i don't have rear passengers. can't hurt to have the rear fill option available.

anyway, thanks man.

elduderino

Any chance of a cold solder? Just wondering...

Cool.

Actually, they would have nosie even when the stereo is off, if that were the problem... I should have said that.

The Head unit ground MIGHT make a diff on the alternator noise, but it's not going to have anything to do with the distortion. I personally would unplug the OE amp and temporarily snap some red T-Taps onto the other two channels (+) and (-) lines, hack the end off of some cheap-ass RCA, and see if the other two channels sound the same. Unfortunately, at this point I am suspecting the wiring (sorry, dude).

Yeah, but wouldn't you rather use the fader to control the relative levels of woofer to mid/highs? : )

You're welcome - good luck.

One more thing to verify - does the distortion happen on BOTH L and R channels?

palidanx

hey electro, you said you move the trunk ground around? care to elaborate a little bit on that?

davestar

ok, first thing... holy f*cking sh*t. troubleshooting nightmare. i worked on my head-unit distortion problems today for the first time in a month, and it wasn't pretty. here's a summary:

my only issue at the moment is distortion. after some critical listening, it appears that distortion creeps in on bass drum kicks and wide-spectrum (loud lows, mids, and highs simultaneously) passages. this indicates a grounding problem, because the amp's current draw is greatest during these times. however, my amp's ground is fine - as i mentioned before, it sounds perfect off a floating CD-walkman. today i hooked up the head unit's pre-amp outs to a home receiver and listened for distortion on that setup - it was fine. this assured me that my soldering job at the pre-outs was NOT causing distortion. it appears the combination of head unit and amp is what is killing me.

i tried to grab the head unit ground at the chassis and tie it to the fuel pump ground that the amp uses, but i'm not sure if the ground point i redirected was actually that of the head unit. (the ground i tried was above the factory amp on the left side. it was held in place by a bolt that faces away from you in the driver's seat) either way, it didn't fix the distortion.

can anyone confirm/disconfirm if this was the ground of the head unit? other suggestions?

elduderino

I am still not convinced that your HU ground is at fault. I don't think that approach fits Occam's razor...

If you do have a problem between your HU and your amp, another possibility is that the amp doesn't like RTO voltage drops during peak OP. We had some Rockford amps and some Pioneer decks back in the day that showed this issue with each other. Is your RTO coming from the deck? If so, temporarily disconnect it and tie the amp RTO input to B+.

Also, try inserting a preamp device (xover, eq, line driver etc.) in between your HU and your amp to see if isolating your amp from your HU fives the problem. If there is some sort of mismatch between your HU and your amp, such a device might take care of the problem.

Have you tried a different amp?

davestar

ah, good suggestions. i briefly checked the RTO voltage, which appeared to be a solid 12.18 V. however, i wasn't checking for dips, but rather an absolute value. i'll look into that more.

impedance matching on the input. doh! i should've considered that earlier.

thanks for the tips - hopefully i'll get to test this stuff this afternoon.

(btw, what's this "Occam's razor"?)

jiggaman

my audio sounded like shit until i incorporated line drivers into the setup. my tweeters were crackling etc. and the louder i tried to play it the worse they sounded.

davestar

thanks jigga... this impedance mismatch sounds more and more likely

elduderino

From Wikipedia:

Occam's Razor (also Ockham's Razor or any of several other spellings), is a principle attributed to the 14th century English logician and Franciscan friar, William of Ockham that forms the basis of methodological reductionism, also called parsimony.

In its simplest form, Occam's razor states that explanations should never multiply causes without necessity. When two viable explanations are offered for a phenomenon, the simplest full explanation is preferable. If a charred tree is on the ground, it could be because of a lightning strike or because of a secret government weapons program. The simplest explanation that is sufficient is the logical one, according to Occam's razor, and there was a lightning strike.

Occam's Razor is nowadays usually stated as follows:

Of two equivalent theories or explanations, all other things being equal, the simpler one is to be preferred.

davestar

well, a little update that might help others t-shooting (though DIY installs hardly seem the norm here...):

i picked up an AudioControl Matrix 6-channel line-driver. it can take a 2-channel input and split it to 4 or 6 channels, each with independent gain control, so it's perfect for me. plus i picked it up used for only $50.

anyway, the purpose behind the line-driver was to lower the output impedance of the head unit to better drive the first-stage of my amp (thanks again eldude). well, it worked quite well. everything sounds as crisp and clear as i could hope for - even at near-intolerable volumes.

left to do is move my crossovers - they're currently on either side of the stock amp. the inductors pick up some alternator and CD-player motor noise. i think there's room under the gear-shifter, so they'll be there sometime soon.

pics coming if anyone's interested.

elduderino

Good news! Well done!

I think the Matrix is discontinued, but you can still find some on the internet (I found a new one for a project some months ago). You can also use any AudioControl xover product, as they have line drivers built into them on th output side. I ahve been considering using one as a subsonic.

Those xovers - do they pick up engine noise even with the stereo off? (That's the mark of the inductors in the xovers picking up EMI like little antennas... engine noise while off)

I put mine under the firewall carpet on the passenger side (the plastic carpet backing is hard, and the Alpine SPX crossovers were huuuuge.)