Help with Hissing

[ogilybogil]

(hand) Hey,
Well, I just installed my 6.5 components in the front, and my 110x2 channel amp and am getting some faint hissing. I have the stock head unit and a Dave Navone 774Variable LOC. I have done quite a bit of playing around with the pots on the LOC and also the Gains on the amp. I cannot seem to get rid of the hissing. They seem to go up as I increase the gain and also as I increase the signal strength through the LOC. How do I measure voltage coming out of the LOC? My amp is rated at 250mV - 2.5V input, so I guess I dont want my LOC to put out more than 2.5V? Also, what should the crossover hertz be set at? It is 50Hz-5.5KHz variable 12dB. Thanks,
Jeff

 

[Poseur]

The printed numbers are fairly difficult to really balance. Basically if the hissing increases when you up the output of your LOC, I'd look at your wires running to your LOC, and possibly the power and grounding of it. if it only increases with your amp sensitivity being turned up (lover voltage) then I'd check your RCA wires, and make sure they're not running near any power wires, and that the ends are wrapped up and not touchign anything metal. After that your grounding would be the next place to focus on. Make sure you've got a good clean ground with exposed body metal that it's contacting...

As far as your crossover, with 110w going to 6.5's I'd try to keep it at 80hz high Pass for the very lowest and possibly a bit higher, say 120. The reasoning for thsi is that with your mids and highs, the thing that'll kill your speakers the most pushing them with lots of juice is low frequencies, so the higher you can set them and still not be able to "locate" your sub blatantly the better. (I'm assuming you do have a sub) You'd then set your sub to low pass at about the same (80-120range) possibly a bit higher so that you have a bit of overlap...

 

[Mercure]

Poseur has good suggestions.

I am confident it's not the LOC nor how the pots are set. If you could fix the problem by turning down the pots, it wouldn't just make the hiss quieter, it would cut out the hiss. When you're hearing more hiss by turning pots or amp gain, I think you're just amplifying the interference problem which already exists. I thought the same LOC was maybe messed up or something, and I also thought that turning the pots would help somehow. But when I fixed the real problem, I turned it all the way up again and it sounded and worked great - I was just messing with the LOC because it was a knob and I didn't understand it. You should not have to turn down the pots a lot if you do at al, and the extra voltage doesn't hurt, at worst you just have to turn it down a bit, but you definitely don't need to calculate anything.

The power cable location could well be it, you want to have this right anyway if it's together with signal bearing cables.
Be sure you have a really good ground. Bare metal to bare metal, and good firm contact (e.g. bolt holding it to the surface). I have heard about this causing noise problems.
And especially check your connections. Things can slip or pull a little loose sometimes and the connection isn't as good. A little strand of wire can touch something and introduce weird interference which you can just avoid diagnosing.
I guess if you get stumped, you might make sure the HU isn't putting out a hissing signal!

 

[ogilybogil]

1. I have no subwoofer yet. Could only afford the front half of the car, so far. In the works.
2. I have lengthened the wires going into the LOC from the head unit. I used the same gauge it came with ( I think its about 16 guage) and soldered it at both ends. Would this wire cause any interference? It runs next to the remote wire and also a small length of the RCA's.
3. The power wire is on the opposite side of the car, and the ground is grounded to scraped/bare metal under the e-brake lever.
4. I assume that amp sensitivity is the gain?
5. I am going to perhaps rewire the LOC to the back of the head unit. Is their a place I can get a new harness. I know that one of the wires, I cut a little short, and didnt have the best connection, it was good, but no the best. Is it possible to get rid of all hissing with an LOC? Am I asking for something that cannot be done? Thanks,
Jeff

The printed numbers are fairly difficult to really balance. Basically if the hissing increases when you up the output of your LOC, I'd look at your wires running to your LOC, and possibly the power and grounding of it. if it only increases with your amp sensitivity being turned up (lover voltage) then I'd check your RCA wires, and make sure they're not running near any power wires, and that the ends are wrapped up and not touchign anything metal. After that your grounding would be the next place to focus on. Make sure you've got a good clean ground with exposed body metal that it's contacting...

As far as your crossover, with 110w going to 6.5's I'd try to keep it at 80hz high Pass for the very lowest and possibly a bit higher, say 120. The reasoning for thsi is that with your mids and highs, the thing that'll kill your speakers the most pushing them with lots of juice is low frequencies, so the higher you can set them and still not be able to "locate" your sub blatantly the better. (I'm assuming you do have a sub) You'd then set your sub to low pass at about the same (80-120range) possibly a bit higher so that you have a bit of overlap...

 

[DZnutz]

sorry i cant help you too much but you might want to pull the remote wire along your power wire as opposed to along your RCAs. the remote wire carries a 12V power source as well so it will cause some interference

 

[Poseur]

If you're running no sub, then what I'd do is turn your crossover off, and just run the speakers fullrange. You'll have to be a bit easier on the gains (sensitivity) but getting full-range sound is more important than getting that extra bit of volume.

The remote wire shouldn't really carry enough current to do much, but it wouldn't hurt to run it seperate. One thing worht giving a shot if at all possible is to one-by-one run sections of wiring over your seats, etc basically in the open where you know they'll not pickup any weird interferance, so say start with the RCA's run a set from your LOC to your amp directly without tucking them in. If that makes no difference, try a different ground. Heck if you've got a set of jumper cables you can try going directly from your battery. YOu could then try to figure a way to just disconnect your wire going into your LOC and re-run some speakerwire again out in the open to it. Kind of a PITA, I know, but that's sort of just how it goes...

Question, though on your speaker-wire that goes form your amp to your doors. did you pull new wire? or ar eyou patching back into the factory stuff behind the deck? I doubt it'd cause hissing, but with that kind of power you might wanna replace that skinny stock stuff. Just that's a little much juice for that little wire.