Low volume distortion during installation

I'm installing CDT components in the doors, run by a Cadence Q4000 and the stock HU. This is in a mkiv Supra using the high-level inputs (from after the factory amp) on the Cadence. I have one mid in the door so far and I wired it up to test the amp and wiring. With the gain on minimum and the HU volume relatively low, it is already distorting. If I turn up the gain, the distortion actually lessens. With the HU volume up and the gain at min (to set the gain according to Cadence), there is enough distortion that I don't want to turn up the gain any. Without music playing, there is minimal noise.

Any idea why I'm getting distortion at such low music volumes? Or why it improved when the gain was turned up part way?

Here's my guess: it isn't quite distortion, but rather some sort of electrical noise. Increasing the gain just hid the noise. I can't say I've ever used high-level inputs, but I assume the gain setting procedure is the same as with RCAs. Pros? Set your gain and leave it. Then troubleshoot the noise problem. In my experience many noise issues go back to grounding problems. Check out the excellent grounding stickies at the top of the forum.

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New Project: 2003 Pathfinder

The only ground I've added is for the Cadence amp and it is grounded at the same point as the stock stereo. I did not sand off the paint at this location, should I?

There is also a ground wire in the little high-level harness on the amp (it has 5 wires: pos and neg for each channel and the ground). I have not connected this wire to anything, does it need to be grounded as well?

The wire that you connected between the OEM wiring and the amp high level input may be picking up noise.  A cure is to twist that signal wire, + and - around each other at 1 to 1.5 twists per inch.

And, the stock system might be "premium" which might consist of original low impedance speakers.  If that's the case you should use a special adaptor to get a usable preamp level signal from the head unit.

The ground wire on the high level harness would not be used.  It's there for use with common ground car audio systems.  If you got no sound at all, then connected the ground, you would get sound if that were the case.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

I used a shielded 4-wire 22awg from the OEM wiring and the amp high level input. Is having both channels twisted together a possible problem?

The stock HU puts out a low level signal (with one wire for each channel) to the factory amp, which then sends the high level signals to the speakers. As far as I know there's nothing special about the output to the speakers, so I have sent this signal to the Cadence amp. Ideally I'd get rid of the stock amp (5 lbs I don't need), but the power and other connections for the HU come from it and I'm not sure how I would set that up.

The twisted wiring would not be a problem.

The grounding is a potential reason for the noise.  If you can't fix it that way, try an aftermarket adjustable line output converter instead of the amp's high level converter.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Also, yes, strip the paint at your amplifier's gound point. It will thank you. :-)

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New Project: 2003 Pathfinder

I'll strip the paint and check the grounds tonight.

I'd like to use a nice LOC such as the PAC OEM and remove my dead weight factory amp, but I'm not sure how to do the wiring. Has anyone kept the HU and replaced the amp in a Toyota with a separate factory amp?

Some Toyotas use the processors in the amps to do all the balance/fade controls.  That being said, it may be easiest to take signal after the factory amps to connect your LOC's.

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My ex once told me I have a perfect face for radio.

I ground off the paint down to metal at my ground. No difference. I installed the mid on the other side and have the same noise problem with that speaker. Could the high level inputs on the Cadence be that lousy?

According to the electrical manual, the wires in the harness from the stock HU to the stock amp are power, acc, FL spkr, FR spkr, RL spkr, RR spkr, mute, beep, fade, and antenna. Ground is in the shielding. This makes me think that the amp must be controlling fade, if not balance.

No, the head will more than likely send a signal for each speaker and a common ground for all speakers to the hidden amplifier. The factory head will still control the fade and balance. You must attach the LOC wires after the hidden amplifier. The simplest way to do this is to find either the front or rear speaker wires and tie into them. Another good suggestion here is to not use the built in LOC in the amp, buy yourself a good outboard LOC from PAC, Soungate or Scosche. These are far superior and offer far more flexibility than the built in LOC does, especially in the amount of signal that the amp receives.

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Top Secret, I can tell you but then my wife will kill me.

Finally got back to this, I think I'm going to buy an LOC, but I'd like to make sure it will help before I spend the $$.

One other question I have, will noise and resultant crackling of the sound lead to weak bass? The 6.5" mid is mounted on a custom 1/2" mdf baffle with deadening and using the door as an infinite baffle, and the bass is pretty crappy (it doesn't compare to the factory Bose in our '97 Maxima). Or is this most likely a problem with the speaker install itself? There is a large opening with no metal in the inner door where the little factory speaker box was. I did not reinforce this (mdf baffle is just large enough to hold the speaker in place and does not cover the hole) but just laid the deadening over it. Could the deadening be flexing enough to trash the bass or is something else the problem?

Finally got a David Navone NE-774V and hooked everything up tonight and.....much better. I don't get any distortion now until much louder volumes. I do have a couple more questions though:

1. Gain setting: the LOC says to keep the gains at max if possible. Doing this barely allows me to raise the gain on the amp before hitting distortion (at a reasonably loud level, but it seems to me it should be better). How do I properly set these (I don't have a test CD)?

2. From my post above, do I need to better reinforce the deadening over the holes in the inner door? I'm looking for SQ here and am not sure how important that is to the speaker performance.

I would suggest using your DMM to measure voltage while setting the LOC.  You can use the amp's speaker output terminals while the gain is all the way down.  When the voltage is at (or near) the maximum input the amp will allow (look up the voltage input range in the manual), then use the amp's gain.  In a perfect world, the amp's gain will have to be turned just slightly to match the input level, as that would be the greatest signal to noise ratio.

Layer the door panel with solid damping including covering all the holes.  The baffle that your driver is mounted to must feel solid when you push against it.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.