Hissing! simple car-audio set-up... help :)

[badmonkey]

Well I figured I would try this here cos I'm sure some of you DIY'ers have some car audio experience!

This is very simple, it's just a head-unit with standard wiring and stock speakers. Just installed a new Pioneer DEH-P5150UB replacing an old Alpine in my 2002 Ford Mondeo. I am using bought harnesses to connect the HU: one from the Ford plugs to an ISO socket, then another from the ISO to the Pioneer.

There is no amp and the previous system worked fine (or appeared to anyway).

I am getting a small about of hiss (pink noise) from the unit which is noticeable when playing CDs, during quiet sections of music or if paused. The level of the hiss is related to the volume - pause the music and max the volume, and it's quite bad.

It does not vary with the car engine, and is not affected by any of the car's controls or mechanics that I can detect.

I am not using RCAs, just the all-in-one wiring harness.

I tested the ground today: disconnected +ve from battery, ran cable from -ve to the cabin and measured resistance between that and the ground on the harness. I get 0.9 ohm. That's okay right?

Played around with the harness wires while I was out there, didn't make any difference if I moved them away from each other etc. I tried wrapping the battery and ACC cables with foil, made no difference.

Any other things I should be looking at?

 

[lynxkcg]

My pioneer HU gave me crap until I wired in a 10 guage ground wire directly to the nearest dash bolt, the ground wire in the stock harness just wasn't cutting it. Integrated amps in the HU are just as bad as any other integrated amp, but it shouldn't be terribly bad and certainly not worse than a lower end alpine.

 

[cobaltmute]

This may a better place to ask questions:

Car Alarm, Car Stereo, Mobile Video, and Cruise Control Info for Installers

But I would check your grounds. Don't use the harness ground - find the nearest ground bolt on the car and run a wire to it. Had a similar problem with a DEH-P880PRS.

 

[badmonkey]

Thanks guys, although I'm confused as to why a separate ground would be necessary if the existing one seems to be measuring okay?

If I did install a new ground, are you suggesting that it be spliced into the existing harness plug so as to connect to the socket on the HU, or somewhere else on the HU? (There is no ground screw or anything that I can see).

 

[Steve Eddy]

If it is indeed a pink noise-like hiss, then it's not a grounding issue. It's noise being generated by the internal circuitry of the unit. Most likely it's inherent in the design of that particular unit, though there is a possibility that it's a bad unit. If it's not too much trouble, see if you can return it and try a different one.

SOME amount of hiss (even if it's barely audible) is normal in every electronic circuit. The amount can vary depending on different designs, particularly with regard to how much gain the circuit has. More gain generally means more hiss. That the level of the hiss changes as you adjust the volume means that the circuit that's the source of the hiss is located upstream of the volume control.

k

 

[badmonkey]

Thanks Koyaan, it sounds like pink noise to me. I just went and recorded it, so here's a demo:
<edit, link removed>

You can hear the hiss, this is at full volume with a CD paused. I alter the volume a little up and down. You can hear a slight "thumping" with each volume step on the way down, nothing on the way up. I also select the track-next function, and that creates the very obvious electronic tone you can hear (the clicking and chirp beforehand is the physical button push).

So, all in all, would you maintain that it's the unit, not the wiring/ground etc?

I know a little hiss is normal but this is much more than I'd consider acceptable. It's quite audible at a moderate/high volume even with the car engine running. I'd compare it to tape hiss in the bad old days!

 

[Steve Eddy]

Thanks!

Yup, that's hiss alright. Well, at least until you get to the nasties that happen when you do the next track selection.

I can say with a fair amount of confidence that the hiss isn't the result of any grounding issue, and the nasties with the next track selection leads me to further believe that there's something wrong with the head unit internally.

Would it be too much trouble for you to take it back and swap it for another unit?

k

 

[badmonkey]

Yeah I can take it back, I just wanna be 100% sure before I do. The first question they'll ask is "was it professionally installed", and when I say "no" to that I had better be in a position where I know what I'm talking about.

If I run a cable from the battery -ve around into the cabin, where on the unit would I (temporarily) connect this to, in order to check for certain it's not a ground issue? As I said above, I can see no ground point. Either way is this safe, with it all powered up and running?

What I'm saying is I want to do something like this so I can say as much to the Pioneer guys, to eliminate all excuses for them.

 

[Steve Eddy]

You'd need to try and trace back the ground lead, which may be a bit difficult since the wiring harness you're connecting to is ultimately built into the vehicle.

I can't find the manual for the 5150 but neither the installation manual nor the owner's manual for the 5100 had any information on the pinouts for the ISO plug on the back of the unit. However it does show that the ground lead in the wiring harness is solid black. If the wiring harness you're using adheres to the same color coding, then your ground lead would be the black wire.

k

 

[badmonkey]

Yes that's the same, it's not an ISO connector (typical) on the head-unit but I have an ISO-to-Pioneer harness. The car's wiring has two grounds, a "12V -ve" and a "chassis" wire. The Pioneer harness runs them together into a single connection for the Pioneer plug.

So you're suggesting I splice into that (the Pioneer connector) a new ground, run ideally from the battery -ve? Since the resistance between the battery -ve and the harness ground is already measuring quite good (0.9 ohm), this won't do much right? (I thought the idea was to ground separately to a different point on the head unit). Or is it pointless, and I can just quote the 0.9 ohm measurement to the folk at Pioneer when they try to tell me it's the car's fault.

 

[Steve Eddy]

Quote:

Originally Posted by badmonkey /img/forum/go_quote.gif Yes that's the same, it's not an ISO connector (typical) on the head-unit but I have an ISO-to-Pioneer harness. The car's wiring has two grounds, a "12V -ve" and a "chassis" wire. The Pioneer harness runs them together into a single connection for the Pioneer plug.

That makes sense.

Quote:

So you're suggesting I splice into that (the Pioneer connector) a new ground, run ideally from the battery -ve?

Well, you were the one wanting to run a cable directly from the battery to the head unit, and you said you saw no ground point on the head unit. I'm simply saying that that's where you'd want to tie in the ground wire.

Quote:

Since the resistance between the battery -ve and the harness ground is already measuring quite good (0.9 ohm), this won't do much right?

I wouldn't expect it to, no.

Quote:

(I thought the idea was to ground separately to a different point on the head unit).

I don't know. Where did the idea come from? Perhaps you misread something?

Quote:

Or is it pointless, and I can just quote the 0.9 ohm measurement to the folk at Pioneer when they try to tell me it's the car's fault.

I think it's likely to be pointless, but it doesn't hurt to cover all bases possible when you're returning something. If it won't be a lot of trouble, I'd say go ahead and do it anyway.

k

 

[badmonkey]

Well I took it back today, and the guy plugged it into his rig there at the workshop, and it's working fine! Played music etc, volume up full and paused, dead silent.

Unfortunately I forgot to take the harness so I'll go back tomorrow and get the guy to listen in the car.

In the meantime, the only difference I can think of between the old Alpine (which works fine) and the Pioneer in the car is the Alpine's harness, which has some electronic goodies wired into it. The Alpine install manual (page 28) lists these items as a choke coil and a fuse holder. I'm guessing that since it's obviously part of the Alpine product, the coil shouldn't be needed for the Pioneer...?

Other than that I'm stumped and out of things to try.

 

[SiBurning]

0.9 ohms sounds high to me by a factor of 10. With a 4 ohm speaker, you're using 15% or so of the current to heat the wire. Figure that's a 1 ohm resistor in the wrong place of the output circuit.

What kind of cable are you grounding with?

 

[badmonkey]

The ground is just the stock car harness. The 0.9 ohm figure is the resistance between the battery -ve and the ground. I used a jumper cable to get from the battery to the cabin so I don't know how much resistance that represents. Bear in mind the previous head-unit (Alpine) works perfectly with nothing different, as described in my last post above.