Any ideas? 12v amplifier plugged into laptop

**AussieM8** · 08-10-10, 12:17 AM

Hi guys

I had an old PC for playing MP3's which was connected to a car amplifier and wired to a couple of outdoor speakers. Worked fine until the PC crashed and I decided to replace it with a laptop.

I bought a 2nd hand Dell D610 but when I play MP3's and plug the amp into it, the sound is all garbled as if the levels are way too high. In fact, it's actually impossible to hear it properly with the speakers popping and crackling. Even with the soundcard levels down to almost zero, it's not clean sound.

I suspect that the onboard sound on the old PC wasn't amplified, whereas the lappy is. Does that sound correct? If so, is there any way of switching off the amplified output of the lappy and let the external amp do the work?

Any ideas of what could cause this if I'm not on the right track?

**best4less** · 08-10-10, 12:41 AM

You are spot on, I know with the old sound cards you could move a jumper to make the output amplified for headphones or use the output as a line output (not amplified ) like you had for your powered speakers

I think the easiest way out for you would be a USB sound card

**AussieM8** · 08-10-10, 11:18 PM

Yeah good idea ... I'll google to see if there's any way to disable the amplifier, but a USB sound card could be the way to go. Cheers M8

**mtv** · 09-10-10, 12:26 AM

I've used these.... they work very well.

**Reschs** · 09-10-10, 01:45 AM

The Car Amplifier is looking for a line level input which should cope with the headphone output of the laptop.
Silly question. Have you plugged headphones into the laptop to check the output?
Another possibility is there is an earthing problem caused by the Laptop not being earthed.
You do not state how the Car Amplifier is powered.

**nando** · 18-10-10, 10:48 AM

try a line level convertor, Jaycar has one with adjustable attunuation:

Cheers,
Nando.

**AussieM8** · 24-10-10, 11:08 AM

Thanks for the suggestions ... I think I might need to do some testing on the actual amplifier.

**AussieM8** · 24-10-10, 11:09 AM

Originally Posted by Reschs

The Car Amplifier is looking for a line level input which should cope with the headphone output of the laptop.
Silly question. Have you plugged headphones into the laptop to check the output?
Another possibility is there is an earthing problem caused by the Laptop not being earthed.
You do not state how the Car Amplifier is powered.

Sorry. The amplifier is powered by a 12v AC adapter.

**Reschs** · 24-10-10, 07:22 PM

Originally Posted by AussieM8

Sorry. The amplifier is powered by a 12v AC adapter.

Just to get this right, a car amplifier needs 12V DC at, at least, 10 Amps.
So by "12V AC Adapter" you mean a 240V to 12V DC supply.

**AussieM8** · 24-10-10, 09:47 PM

Originally Posted by Reschs

Just to get this right, a car amplifier needs 12V DC at, at least, 10 Amps.
So by "12V AC Adapter" you mean a 240V to 12V DC supply.

Oops...yes, I meant 12V DC adapter (with 240v power plug).

This is it:

**mickc** · 24-10-10, 10:55 PM

have used amplifed pc speakers on laptops many times
car amp should be no different
test your laptop with some pc speakers or headphones and see what happens

**Reschs** · 25-10-10, 12:47 AM

Originally Posted by AussieM8

Oops...yes, I meant 12V DC adapter (with 240v power plug).

This is it:

Ok the power requirements are a lot less.

Back to basics.
This set up worked with your PC before it died.
The only change you have made is to replace the PC with the Laptop.
If this is the case, use the volume control on the Laptop sound card to turn the volume down.

Just reread your original post.
Check the Laptop with headphones.

**AussieM8** · 07-11-10, 11:31 PM

Finally got a chance to work on this over the weekend ... and after lots of testing, I narrowed down the issue. Just not sure how to solve it

.

Through the process of elimination, I discovered that when I removed the lappy from the docking station and mains power, it worked perfectly. I tried another Dell power supply and had the same sound problem.

Initially, I thought the sound levels were too high but even with the amp volume turned down to zero, it starts to 'pulse' every second or so.

Could this be in line with Reschs suggestion about an earthing problem? Any other ideas how to stop this issue?

**AussieM8** · 07-11-10, 11:43 PM

Oh, and I forgot to mention - I've plugged the lappy output into another amplifier (ie. audio-in on a midi stereo system) and there is no sound problem when the laptop is powered via mains adapter.

**Reschs** · 08-11-10, 06:36 PM

Sounds like the switchmode power supply for the laptop is radiating rubbish into the car amplifier.
You can try moving the power supply as far away from the Amplifier as the leads will allow to see if the noise reduces.
Next step to try is to get a torriod from Jaycar or Altronics and wrapping a few turns of the amplifiers input cable through it.

**AussieM8** · 08-11-10, 08:31 PM

Thanks reschs :-)

I've never heard of them before .... is this what you mean?

**Reschs** · 08-11-10, 09:20 PM

Originally Posted by AussieM8

Thanks reschs :-)

I've never heard of them before .... is this what you mean?

NO.

Sorry should have been more specific.
What you need is a toroid core. eg CAT. NO. LO1230.

You feed the input cable through it and then loop back through several times.

**AussieM8** · 09-11-10, 06:06 AM

Excellent - thanks mate. I'll head there on the weekend and grab one (or six

)

**AussieM8** · 18-11-10, 10:53 PM

Not much success I'm afraid.

I purchased the cores from Jaycar, but the lead only wraps around it a couple of times before it's too tight (I also had to removed the audio jack). How many loops would you typically need?

Would it be better if I purchased larger cores so the centre hole is bigger and I can get more loops through?

**Reschs** · 19-11-10, 09:46 PM

Originally Posted by AussieM8

Not much success I'm afraid.

I purchased the cores from Jaycar, but the lead only wraps around it a couple of times before it's too tight (I also had to removed the audio jack). How many loops would you typically need?

Would it be better if I purchased larger cores so the centre hole is bigger and I can get more loops through?

Did it at least reduce it ?

I have a busy weekend workwise so I will re read the the whole thread next week.