Nerd2

Well I know ****-all about Car audio, but I wanted to get rid of my head-unit. I got a 2-channel amp off the bay, and have just wired it up.

Anyway I know noise has lots of troubleshooting pages all about, and i'm working through them. I just wanted to know if it was possible that the problem is I am using the stock speakers in my Mondeo, and if I upgraded them it would be likely fixed........

Amp is VRX-VR1502C

Thanks,
Sam

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Dennis5587

depends... how did you tune your amps?.. you could be just hearinh them clip...

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Nerd2

Humm, gonna sound stupid but what do you mean by tuning?

Turning down the gain on the amp helped Still a crackling when no music is playing. No noise when connected to head unit. Just reduced my ground cable to around 6" long as well.....

Oh, and no noise if I unplug input (RCAs)

Dennis5587

:sigh:... okay... an amplifier does exactly what it sounds like it does... it amplifies, the stereo's signal.

That gain setting, is actually just a little knob that lets you match up your amp, with your speakers... it is not a volume knob...

you're going to need an AC volt meter to tune the amp. Next you'll need to know how many watt's you want to tune it to, as well as at what ohm rating...

You take the square root of the watts times ohms... meaning sqrt(watts X ohms) if that helps...

This will tell you how many volts you would need, then next thing you do is hook up that ac volt meter to the amplifier, then pop in a cd with a test tone of 1khz, you can download this off line. Turn the stereo up about 3/4 of the way, then set the gain at that voltage that you figured out before...

Never turn your stereo past that point any more, for at that point, it is the max amount of watts that your amplifier should be pushing to your speakers...

So basically, lets say that your speakers are 25watts rms at 4 ohms...

Take the square root of 25X4... which is 10.

Pop that 1khz cd into your stereo, then set the gain on the amp so that it displays 10V AC...

done

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Nerd2

Brilliant. Thanks for the info. I'll try it in the morning!

Dennis5587

just make sure you find out what the rms watts and ohms are of the stock speakers are

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Nerd2

Thanks loads for your help! I'm getting there! :-)

To simplify things i'm ignoring the whole serial/parallel config of my 4speakers->2 channels and i'm just working with one speaker.

20W rated speaker, measured at 4 and a bit ohms by my voltmeter. I'm struggling to find specs online, so i'm presuming that they are 4ohm speakers.

Firstly, why do you say put your stereo at 3/4, why not full? If that's the maximum?

Anyway, i'm turned my gain to give Sqr(80)=8.95V across the speaker when playing a 1khz tone in XP, and I still have crackling when no music playing....

The thing I don't get is it seems to be signal-dependant, in that when I move the mouse, the crackling intensifies. However the headunit doesn't pick this up at all. That would lead me to believe the usb cable for the mouse is interfering with the amp, and not the headunit. But the headunit is wired very similarly near the amp, and with much smaller, worse wires. (Headunit using a cassette-mp3 adapter).

This is all running from an external sound card, which is a bit rubbish, and could be the problem, but then again why does the headunit not have a problem?

I suspect the next thing would be to move the usb cables around, but that's a right pain

Help appreciated!

Thanks loads

kevinlekiller

If you put the volume at max, then you create clipping ( distortion ).

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kevinlekiller

Can you record this "crackling" noise? Its hard to imagine something we cannot hear , might help us find the problem easier.

Nerd2

I have numerous things I could 'put at max'. Such as the external sound card volume, main windows volume, windows "wave" volume. Will I create distortion if say two are on max?

Crackling attached, in amr form (realplayer'll play it). After about 6 seconds you can hear the different tone which is when I move the mouse. I did try converting to wav but it buggered up.

I'm going to have to pack it in for the moment though, off to uni/college soon. Appreciate any ideas for when I have another go though. :-)

Attached Files

	Sound clip(02).zip (25.8 KB, 35 views)

kevinlekiller

Well , the volume from the sound card is best to be at max , because the higher it is the more signal to noise ratio you get.

He means on the head unit. I cant open that audio file, but I've already had problems with when I move the mouse and hear it in my speakers, it turned out to be a cheap sound card. It was picking up interference from the usb I think. A thing you should try is to mute the mic / line in ports , sometimes noise comes in from there.

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