Reducing Line Level Noise (CarPC)

[spoonraker 10+ year member]

Keep in mind this is a CarPC, not a regular head unit...

First off I have a Creative Audigy SE soundcard. The front and rear channels are connected to a 4-channel amp directly via mini to rca splitter cable. No noise on these channels.

Previously, I was simply splitting the front channel and sending it to my monoblock amp for the bass, but this was a half assed temporary solution. It worked, but I couldn't adjust the bass from the computer.

The reason I did it this way temporarily is because the voltage coming out the bass channel is insanely low and the bass was barely audiable.

Today I went out and bought a single channel line driver which I hooked up to the bass channel. It works perfectly, it amplifies the signal, problem is it also amplifies the noise.

It's really bad, it's a constant loud rumbling noise from my sub, basically what you'de expect noise from a sub to sound like....

Anyway now that all the background and bs is done, the issue at hand is how can I elminate this noise? The computer is at most 3 feet away from the amp, and I have a 6 foot mini to rca splitter running to the line driver, and a 3 foot RCA out of the driver to amp. I'm pretty sure this is part of my problem, but I can't find any shorter cables. Can I just take a big chunk out of the middle of the RCA cables to shorten them and crimp them together, or will that only make more noise?

Basically, what can I do to reduce the noise, this is line level noise, not alt whine.

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[thatkidbob 10+ year member]

Keep in mind this is a CarPC, not a regular head unit...
First off I have a Creative Audigy SE soundcard. The front and rear channels are connected to a 4-channel amp directly via mini to rca splitter cable. No noise on these channels.

Previously, I was simply splitting the front channel and sending it to my monoblock amp for the bass, but this was a half assed temporary solution. It worked, but I couldn't adjust the bass from the computer.

The reason I did it this way temporarily is because the voltage coming out the bass channel is insanely low and the bass was barely audiable.

Today I went out and bought a single channel line driver which I hooked up to the bass channel. It works perfectly, it amplifies the signal, problem is it also amplifies the noise.

It's really bad, it's a constant loud rumbling noise from my sub, basically what you'de expect noise from a sub to sound like....

Anyway now that all the background and bs is done, the issue at hand is how can I elminate this noise? The computer is at most 3 feet away from the amp, and I have a 6 foot mini to rca splitter running to the line driver, and a 3 foot RCA out of the driver to amp. I'm pretty sure this is part of my problem, but I can't find any shorter cables. Can I just take a big chunk out of the middle of the RCA cables to shorten them and crimp them together, or will that only make more noise?

Basically, what can I do to reduce the noise, this is line level noise, not alt whine.

what are you powering the car pc with?

 

[spoonraker 10+ year member]

Opus 150W DC-DC PSU

 

[spoonraker 10+ year member]

Just thought I'd let you all know that I got it all fixed up.

Easiest fix ever, $15 ground loop isolator, done.

Now instead of a 6 foot rca splitter out of the soundcard, then a 3 foot rca cable to the amp, I have about a 4 inch long rca splitter out of the soundcard, then that goes directly into the isolator, that goes directly into the line driver, and that goes to them amp with about a 6 inch long rca cable.

Absofreakinlutely no noise, I love it. Now that my amp is being fed the actual bass channel from a nice computer sound card that sound quality is just absolutely amazing. The bass hits so clean at just the perfect spots, and I can set the exact crossover frequency from the touchscreen without having to even touch the amp.

 

[lincolnls 10+ year member]

is it engine noise?

cause it sounds like you got a ground loop there.

 

[spoonraker 10+ year member]

Obviously it's a ground loop, I hooked up a ground loop isolator and it went away completely...

The wiring is still pretty messy, after I clean it up I'm going to try removing it and see if it still has noise. If it does, oh well I'll leave it in.

 

[.::DuD3::. 10+ year member]

Just thought I'd let you all know that I got it all fixed up.
Easiest fix ever, $15 ground loop isolator, done.

Now instead of a 6 foot rca splitter out of the soundcard, then a 3 foot rca cable to the amp, I have about a 4 inch long rca splitter out of the soundcard, then that goes directly into the isolator, that goes directly into the line driver, and that goes to them amp with about a 6 inch long rca cable.

Absofreakinlutely no noise, I love it. Now that my amp is being fed the actual bass channel from a nice computer sound card that sound quality is just absolutely amazing. The bass hits so clean at just the perfect spots, and I can set the exact crossover frequency from the touchscreen without having to even touch the amp.

what program are you using to adjust the frequency levels? any pics of the setup? im going to be doing a carpc this summer when i get some money.

 

[snoopdan 5,000+ posts]

If its one of those rca ground loop noise isolators, you'll be pleased that you now have both channels out of phase. Ive experimented with this before, it doesnt work so hot if you want to continue to have any competition level SQ.

Best thing ive found was a external USB type DAC

http://www.silverstonetek.com/products-eb01.htm

 

[spoonraker 10+ year member]

what program are you using to adjust the frequency levels? any pics of the setup? im going to be doing a carpc this summer when i get some money.

the program I'm using is just the creative control panel, software bundled with the soundcard

HERE are some pics/vids of my install.

 

[spoonraker 10+ year member]

If its one of those rca ground loop noise isolators, you'll be pleased that you now have both channels out of phase. Ive experimented with this before, it doesnt work so hot if you want to continue to have any competition level SQ.
Best thing ive found was a external USB type DAC

http://www.silverstonetek.com/products-eb01.htm

How can a mono channel be out of phase?

This is only on my sub, and there is only one sub, the rest of the speakers are still just rca's straight from the soundcard to the amp, no line driver, no isolator.

If it is out of phase, how do I know? And if it is can't I just switch the speaker wires to put it back in phase like a normal speaker?

 

[Megalomaniac 5,000+ posts]

If its one of those rca ground loop noise isolators, you'll be pleased that you now have both channels out of phase. Ive experimented with this before, it doesnt work so hot if you want to continue to have any competition level SQ.
Best thing ive found was a external USB type DAC

http://www.silverstonetek.com/products-eb01.htm

that looks neat but i wish it has optical..

 

[thch 10+ year member]

the phase should not be affected, unless the wiring is backwards.