cuhockey32

All - Am a newbie to car audio. Had a local audio shop install aftermarket amp (GM-DX975 Pioneer) speakers (hertz dsk165.3, DCX690.3) and LC7i Six Channel Converter (Audio Control) and 10" PIoneer sub (TSD10D4). Am getting a constant white noise through the speakers that doesn't go away. The shop set all the gain properly on the amp and was confused as to where the noise was coming from.

I've read several folks bypassed the factory amp but it's still confusing as to whether I need to keep the center speaker running through the factory amp for HFL and Bluetooth control.

I'm reaching out to other local audio shops to see if they can help but would appreciate opinions on what to recommend to them.

Thanks for any help.

mossman77

I tried replying to your PM, but it won't allow me to because your inbox is full.

I was thinking you had alternator whine, in which case getting an amp with differential inputs would likely resolve the issue. I'm not sure if this would solve the white noise, but it wouldn't hurt. I believe there's a jumper inside the LC7i that can be switched to isolate the ground. You could try that and see if it helps. Did they connect all the ground wires to a single point and to bare metal? Did they run the power cable on the left side or right? I believe the audio source wires run along the right side. Not positive.

If I were to do it over, I would have run a pair of RCA cables all the way to the head unit and tapped into the L/R channels up front rather than the trunk. That way the signal would have been cleaner and not be picking up any noise on the trip back to the trunk. However, my amp has differential inputs, so the noise is filtered. Although I do still hear some faint white noise, but the music drowns it out. That could be a gain thing, so be sure they set the gains properly (are you sure they did?)

You do not need the center speaker. The bluetooth, etc voice prompts will play through the L/R speakers.

Here's a 5-channel amplifier with balanced differential inputs: http://www.jlaudio.com/xd700-5v2-car...plifiers-98606

mossman77

A couple alternatives:

1) Simply swap out the Pioneer amp with one that has balanced differential inputs (e.g. JL xd700-5v2)

2) Keep the Pioneer amp but tap into the INPUTS of the factory amplifier (requires soldering RCA connectors) to obtain a low-level signal, then replace the LC7i with another Audio Control product that has diff inputs (e.g. 6XS crossover or Matrix Plus)

3) Swap out the Pioneer amp for the JL xd700, tap into the factory amp's inputs, and omit the LC7i (connect directly from the factory amp inputs to the xd700)

I don't recall Audio Control having the 6XS or Matrix Plus back when I did my system. I went with the DQDX processor, which has 7-band EQs, but found out pretty quickly that adjusting the knobs on the EQ while trying to tune the system wasn't realistic. I plan on upgrading to either a DM-608 (has computer interface) or another advanced processor that allows adjustments on-the-fly from the driver's seat.

mossman77

FYI, here is the diagram for the amplifier input connector (navigation and non-navigation):

cuhockey32

Thanks for the info mossman. Since the post Ive been back in the shop twice. They ended up saying I had a bad amp which caused the speakers to blow. They replaced them all free of charge and... white noise still there.

I purchased a used amp off ebay and that didnt seem to help. I also tried to maximize the output of the LC7i and the white noise gets worse the higher the gains on the LC7i. I have my after market amp gains to zero and the noise is still there.

All grounds are separate and Im getting a good ground for all four points (battery, amp, LC7i and factory amp).

The amp is grounded under the rear seat and the connection is right next to the power wire for the amp. Not sure if this is an issue.

Im starting to wonder if the capacitors in the factory amp need replacing as I saw in another post on some 3G TLs.

Thought?

Bchester6

Have you moved the internal jumpers in the LC7i? Specifically the summing and ground isolator jumpers. Move some of that stuff around and see if you can eliminate the noises you're dealing with.

cuhockey32

@Bchester6 I moved the jumper from isolated to 200 ohm to ground and did not have a change in white noise. I removed the head unit and it looks like the ground for the head unit is on bare metal - although I cannot tell if it is aluminum or steel but both grounds for the front of the car are in this area.

My gains are all the way down on the amplifier and pretty much all the way down on the LC7i and I still get the noise.

That said, I disconnected connector A on the back of my head unit and the noise goes away and this connector has most of the wires that go to the factory amp including the ground wire. At this point, I'm thinking either the head unit is bad or the ground isn't a good one (even though it's as installed by the factory).

I may have to try a ground loop isolator on the input of the amp. Am running out of options and I don't want to waste the money replacing the head unit if I can help it.

A few odd notes about the LC7i install:

The power supply for the amp and the amp ground are routed right next to each other for about 3 feet.
The Remote In for the LC7i is spliced into SWD +B pin B3 on the input connector to the factor amplifier.
The 12V for the LC7i is spliced into the pin 18 No. 15 (20 A) fuse in the passenger's under-dash fuse/relay box white wire coming OUT of the factory amplifier.

Not sure if this helps at all.

Bchester6

I would next ground all of my audio components to one grounding point (including the HU).