computer power lead causing interference

[gavinc]

Dear All,

I asked a question the other week concerning a problem I have when connecting my laptop up to my disco unit. The problem was that I was getting interference, in the shape of a high pitched whine, which you could here in between the tracks when I was doing a disco.

I have since discovered that it is the power lead of my laptop as the problem disappears when I disconnect the power lead and just run off the battery.

Any long term solutions to this problem?

Do I need a better power lead with a better suppressor on it?

Is there an external type Dell battery pack that I could buy , so that I could just run the computer from the battery pack whilst I am doing my discos?

Any answers/suggestions would be greatly appreciated,

Thanks,

GavinC

[ACtheTROLL]

power unit I think

you could try a ferrite ring on the DC side (for gawd sake not on the AC side)
you'll have to experoment with the number of turns

you'll get them from maplins - a 2cm one should be adequate

[Hymie]

ACtheTROLL may be correct, in that it is due to high frequency noise on the DC voltage supplied via the AC adapter. This can be confirmed by directly listening to the laptop audio out via headphones (running off battery and then the mains).

However if the audio output quality is not affected by mains operation of the laptop, then I would suspect that the adapter DC output is earth referenced.

This earthing to your disco equipment may be causing the noise. Earth loop noise is normally in the form of 50Hz hum, and can be very difficult to eradicate.
The high frequency noise from the mains PSU may be finding a route via the earthing. Again, adding a ferrite could fix this, operation of the AC adapter via an isolation transformer (with no earth through connection) may also fix the problem.

[Hymie]

If the noise is due to high frequency noise from the mains switch mode power supply � the use of a linear transformer power supply should solve the problem.

[rojash]

I'm betting that Hymie's second answer hits the spot. And if it IS from the switched mode PSU. then the noise will be radiated, so changes to the power cable probably won't achieve anything - ONLY replacing the supply with a transformer version will do the trick.