I am using a standard 400 W 12 VDC to 120 VAC inverter to power my
laptop in the car. While this works well, lately I've started doing
audio work with the laptop and feeding the laptop 1/8" audio jack output
into an amp hooked into the car radio. While the laptop is plugged into
the inverter, I get much noise over the audio system. I know the noise
is coming from the inverter, so how would I negate it? I've tried about
5 snap closed ferrite cores around the power cable going into the laptop
but they haven't helped. Thanks.

On 23-2-2018 16:22, JBI wrote:
I am using a standard 400 W 12 VDC to 120 VAC inverter to power my
laptop in the car. While this works well, lately I've started doing
audio work with the laptop and feeding the laptop 1/8" audio jack output
into an amp hooked into the car radio. While the laptop is plugged into
the inverter, I get much noise over the audio system. I know the noise
is coming from the inverter, so how would I negate it? I've tried about
5 snap closed ferrite cores around the power cable going into the laptop
but they haven't helped. Thanks.

A differential amp, to get rid of a ground loop.

Or feed both devices from the same minus 12v point.

Or both.

You've tried it with good headphones, right?

On 23/02/18 15:22, JBI wrote:
I am using a standard 400 W 12 VDC to 120 VAC inverter to power my
laptop in the car. While this works well, lately I've started doing
audio work with the laptop and feeding the laptop 1/8" audio jack output
into an amp hooked into the car radio. While the laptop is plugged into
the inverter, I get much noise over the audio system. I know the noise
is coming from the inverter, so how would I negate it? I've tried about
5 snap closed ferrite cores around the power cable going into the laptop
but they haven't helped. Thanks.

Have you considered using a direct supply with an input of 12v and
output to suit most laptops (19V? You didn't say which make you have).
Typical example here, but many others available at all sorts of prices
and quality:
https://www.ebay.com/itm/Universal-DC-15-24V-Car-Auto-Charger-Adapter-Power-Supply-for-Laptop-Notebook-PC/191191789071?epid=560493099&hash=item2c83eb2e0f:g: FEwAAMXQ1ZhThFqB

Hopefully, although also a SMPS it will not produce the sort of
interference you are getting from your 12/120V inverter.

--

Jeff

On Friday, February 23, 2018 at 9:22:38 AM UTC-6, JBI wrote:
I am using a standard 400 W 12 VDC to 120 VAC inverter to power my
laptop in the car. While this works well, lately I've started doing
audio work with the laptop and feeding the laptop 1/8" audio jack output
into an amp hooked into the car radio. While the laptop is plugged into
the inverter, I get much noise over the audio system. I know the noise
is coming from the inverter, so how would I negate it? I've tried about
5 snap closed ferrite cores around the power cable going into the laptop
but they haven't helped. Thanks.

Get rid of the inverter. They are all horrendous noise sources. Run on battery.

On 2/23/2018 9:22 AM, JBI wrote:
I am using a standard 400 W 12 VDC to 120 VAC inverter to power my
laptop in the car. While this works well, lately I've started doing
audio work with the laptop and feeding the laptop 1/8" audio jack output
into an amp hooked into the car radio. While the laptop is plugged into
the inverter, I get much noise over the audio system. I know the noise
is coming from the inverter, so how would I negate it? I've tried about
5 snap closed ferrite cores around the power cable going into the laptop
but they haven't helped. Thanks.

Use a 12V supply for your laptop?

For my Dell Lattitude D630, I can use one like this:

https://www.ebay.com/itm/DC-Car-Air-...M/262961901405

RwP

Sjouke Burry wrote:
On 23-2-2018 16:22, JBI wrote:
I am using a standard 400 W 12 VDC to 120 VAC inverter to power my
laptop in the car. While this works well, lately I've started doing
audio work with the laptop and feeding the laptop 1/8" audio jack output
into an amp hooked into the car radio. While the laptop is plugged into
the inverter, I get much noise over the audio system. I know the noise
is coming from the inverter, so how would I negate it? I've tried about
5 snap closed ferrite cores around the power cable going into the laptop
but they haven't helped. Thanks.

A differential amp, to get rid of a ground loop.

Or feed both devices from the same minus 12v point.

Or both.

I don't know the problem, but a transformer isolator may help or work.

Greg

On 23/02/18 15:22, JBI wrote:
I am using a standard 400 W 12 VDC to 120 VAC inverter to power my
laptop in the car.Â* While this works well, lately I've started doing
audio work with the laptop and feeding the laptop 1/8" audio jack output
into an amp hooked into the car radio.Â* While the laptop is plugged into
the inverter, I get much noise over the audio system.Â* I know the noise
is coming from the inverter, so how would I negate it?Â* I've tried about
5 snap closed ferrite cores around the power cable going into the laptop
but they haven't helped.Â* Thanks.

Has the laptop & car audio got bluetooth?

--
Adrian C

A differential amp, to get rid of a ground loop.

Or feed both devices from the same minus 12v point.

Or both.

or an audio transformer to break the ground loop

A differential amp, to get rid of a ground loop.

Or feed both devices from the same minus 12v point.

Or both.

or see if you can find a 12 to 19V ISOLATED power supply.

Isolated means the input and output grounds are not connected, This will also break the ground loop.

On Friday, February 23, 2018 at 3:45:17 PM UTC-5, Terry Schwartz wrote:
On Friday, February 23, 2018 at 9:22:38 AM UTC-6, JBI wrote:
I am using a standard 400 W 12 VDC to 120 VAC inverter to power my
laptop in the car. While this works well, lately I've started doing
audio work with the laptop and feeding the laptop 1/8" audio jack output
into an amp hooked into the car radio. While the laptop is plugged into
the inverter, I get much noise over the audio system. I know the noise
is coming from the inverter, so how would I negate it? I've tried about
5 snap closed ferrite cores around the power cable going into the laptop
but they haven't helped. Thanks.

Get rid of the inverter. They are all horrendous noise sources.

As is the car itself or anything else operating near it.

Run on battery.

On 21/03/18 14:28, wrote:
On Friday, February 23, 2018 at 3:45:17 PM UTC-5, Terry Schwartz wrote:
On Friday, February 23, 2018 at 9:22:38 AM UTC-6, JBI wrote:
I am using a standard 400 W 12 VDC to 120 VAC inverter to power my
laptop in the car. While this works well, lately I've started doing
audio work with the laptop and feeding the laptop 1/8" audio jack output
into an amp hooked into the car radio. While the laptop is plugged into
the inverter, I get much noise over the audio system. I know the noise
is coming from the inverter, so how would I negate it? I've tried about
5 snap closed ferrite cores around the power cable going into the laptop
but they haven't helped. Thanks.

Get rid of the inverter. They are all horrendous noise sources.

Not all of them. Unfortunately price is no indication however.
We've used quite a few different inverters for our in-car
fox-hunting gear, and some cheapies are quiet, some $$ are
noisy. You just have to suck it and see in most cases.

No, I don't know brands and models - been away from this for
a few years.

As is the car itself or anything else operating near it.

Cars can produce lots of interference, or next to none.
At least with a car you can usually chase down the cause
and perhaps cure it.

Clifford Heath.