blue86iroc

iTrader: (2)

OK, I know that this topic has been beaten to death on this board. I've searched the archives and I've tried everything suggested there, to no avail. I'll start by naming all of the components in my system:

- Alpine 7914 Head Unit
- Three Coustic/Power Logic Amps; one rated at 250W the others rated at 30W (I hear that these amps are very old)
- Two MTX Road Thunder Two 10" subwoofers
- Sentrek Crossover Box (I forget the model)
- Cheap 4x6's and 6x9's (Boston and Pyle)

As usual, the whining increases with the RPMs. I don't see how I could have a ground loop. I recently re-grounded the amps and the crossover box using 4 gauge wire and a distribution block to the same location on the car, right underneath the carpet near the spare tire, directly into the body frame. I sanded the area real good and used a star washer.

I have also grounded the head unit to the body frame behind the passenger kickpanel, as Jim had suggested in a bunch of previous posts. Here too, I used a star washer. However, I used 14 gauge wire instead of 12 gauge (I used what I had on-hand).

The power and remote wires do not run next to the speaker or RCA wires. There are no ground loop isolators on the system, though I do have some.

The RCA cables look pretty cheap, but that usually doesn't seem to cause problems. I replaced the speaker wire with Rockford Fosgate 12 gauge car audio wire.

Honestly, I can't see where the problem lies. A lot of people talk about cheap equipment causing noise, but I don't know how "cheap" my amps are; the entire audio system came with the car when I bought it. The only other thing I could possibly think of is the stock ignition... that could be causing interference.

Please, does anyone know what's going on? I'd appreciate any help that I could get.

Jim85IROC

iTrader: (2)

It could be the amp(s) or the crossover. If the crossover is a real cheap unit, it probably has no noise filter and a really cheap power supply (if any) and will introduce a ton of noise. I put a $20 Pyramid subwoofer crossover into a friend's Trans Am and it whines like there's no tomorrow. Because he's too cheap to buy a better one, I just used a ground loop isolator to eliminate most of the noise, but to do it right he needs a higher quality crossover that has a better power supply. You could have the same problem, or you could have a problem with one of your amps. I'd start by eliminating the crossover from the signal path and see if the noise goes away. If not, play each amp full-range into a small test speaker one at a time and see which one(s) have the noise.

------------------

The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
Custom Thirdgen Subwoofer Enclosures
"I didn't know a bored out Ford could go so slow" -Shenandoah

blue86iroc

iTrader: (2)

Well, I removed the crossover from the system and the whine went away. Of course, my sound quality has degraded because I'm using the deck to drive the amps.

I guess my next question is what kind of crossover should I get? I should be receiving my new Nakamichi CD40z head unit in the mail soon... that has three outputs (front/rear/subwoofer). I had a previous post here about using that head unit with my current crossover which only has one input. I might as well get a good crossover that has three separate inputs to match the Nak unit; do they even make crossovers with three inputs and three outputs?

Driving the amps from the Nak unit isn't an option either, because the amps don't have any built-in crossovers. Speaking of which, should I bother replacing my amps? I understand that they're really old, but they seem to suit my purpose just fine (This is no competition system).

Mike92RS

Is that deck's sub output lowpass, or is it the whole frequency range? Some head units have crossover's built in. If it's just the low frequencies, you could run that right to your sub amp, and just build passive crossovers for your rear speakers, since they're not as critical. It's really not hard at all...just a capacitor and inductor (for 12 db/oct), and you can probably do both sides for less than $10. That's what I did since my amp only has lowpass crossovers on channels 3 & 4. Then you only have to worry about getting a crossover for the front.

- Mike

[This message has been edited by Mike92RS (edited August 14, 2001).]

Jim85IROC

iTrader: (2)

I doubt you'll find a crossover with multiple inputs. Usually you run a single full-range signal to them and they do all the work. Virtually any quality audio manufacturer should have a crossover that will fit your needs. Check Alpine, Pioneer, Orion, Zapco and especially Audio Control. I would say that Audio Control will be your best bet, although their products can be finiky about introducing noise, but once you get everything straight, they're good and quiet.

------------------

The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
Custom Thirdgen Subwoofer Enclosures
"I didn't know a bored out Ford could go so slow" -Shenandoah

blue86iroc

iTrader: (2)

Thanks Jim, I'll check into that. Mike, I'm not sure if the deck's sub output carries just the low frequencies. I'm guessing it doesn't, because the deck doesn't have built-in crossovers. I'll just have to find a good single-input crossover and run the full-frequency sub output into that.