Noise Issue after adding EQ
HI all. I just did a new install in an 01 PT Cruiser. Goal is sound quality.
I am using a Kenwood X966 head unit (was using a Pioneer DEH4200 but changed HU's in troubleshooting this issue - and HU was not the root). The head unit is grounded where the amp under the passenger seat is grounded.
Amp under passenger seat is an old but well-liked RF Punch 800.4. This drives front/rear speakers. The front speakers are RF PPT4-6's and RF P1TS tweeters. 6's are on the doors in stock location using stock wiring, tweeters are in the A pillars, using stock wiring to the point the stock tweeters were in the dash, and the crossover for the tweets is in that location an uses the wiring that came with the tweets for the rest of the run to the pillars.
This amp has 4 gauge power and ground lines. Grounded to the frame near the seat (seats are not motorized). Ground wire is about 2 feet long. Grounding site was sanded with sandpaper.
The power on line comes from the HU and is 12 gauge. Battery power line is 4 gaufe all the way direct to the battery. Battery line and power on lines are run under the center console up to the center of the dash, where the power-on line goes up to the HU and the battery line makes a left under the drivers dash over to the firewall hole for the hood release cable and then to the battery. Battery terminals were cleaned recently.
Audio lines come from the HU via good twisted pair lines that run from the center dash, under the dash passenger side and down the passenger side near the door under that trim.
For FYI but probably irrelevant to the problem, there is a rockford prime sub amp in the rear driving a JBL 10in in a sealed enclosure. That amp is grounded to the chassis in the rear
With the system as above, I can set the gains on that RF 800.4 all the way up -- not that I want to run that way, but to demonstrate there is no noise -- and I in fact get no noise. Well there is a faint hiss because the gains are too high but there is no alternator whine. The gains get set at about 75% in actuality. THe HU is a 3V output I recall.
After runnning that configuration a week, I decided to go for an Audiocontrol EQS. This was installed under the seat with the RF 800.4, getting it's power from the same power line that feed the RF 800.4, and the power-on is also from the one shared by the RF800.4, and it is grounded at the grounding site where the HU and RF 800.4 are grounded. The chassis is not grounded (neither is the RF 800.4, should have mentioned that before).
The problem is with the EQS installed, I set the input gain to zero (it is adjustable from -12db to +12db, with the center being 0). This setting, I presume is to cut or boost the input signal. Since I have a nice strong HU and because going direct to the amp I can get a fine signal (have to cut the gain on the amp as expected), I don't need input signal boost.
I set the output levels on each channel to about 3/4.
Now, the problem is I have to turn the amp gain way down, else I get noise. There is very pronounced alternator whine. If I turn the gain on the amp down very far (like to 25%) that eliminates the whine, but then I can max out the headunit volume and not get close to what the level should be.
I can play with the EQS input level, output level, and amp gain to get the noise covered and still be able to listen at normal volume levels, but it is losing output power and I don't like it.
Noise only seems to be a problem on the front channel, I suspect because I have the tweeters and am sitting close to them, so any whine is going to come through quite clear.
Further testing -- If I unplug the EQS inputs from the headunit, still noise when the HU volume level is at zero. This tells me the EQS is introducing the noise. If I unplug the output RCAs the noise goes away.
This is frustrating and a lot of work to install what should be a quality piece of equipment (seems to get good reviews and be well liked in the industry) into a vehicle that is known to be noise free and end up with noise.
I have to assume that the audio circuitry in the EQS is not low quality, and the power supply is not filtering as it should. I guess I have to start playing with power supply filters, etc.