Electronics > Projects, Designs, and Technical Stuff
50hz mains hum
m3vuv:
Hi all,im trying to run the audio from my lappy headphone jack thru my amp using the headphone output,ive got a 3.5mm male jack to rca converter/adaptor,as soon as i plug it in the lappy i get a terrible mains hum(loud),if i unplug the lappy power adaptor its fine,also i seem to get a lot of 50hz mains interferance on all my psu's and scopes,could this be faulty mains wireing?,any ideas welcom,73 m3vuv.
magic:
Most likely the laptop PSU doesn't connect its secondary side to safety earth so that all the charge injected by capacitance in the PSU stays on the secondary and flows to earth through the audio cable's ground once that is connected.
Do you have differential (so-called "balanced") inputs on the amp?
m3vuv:
no just normal rca style phono jacks.,also the cable for the lappy psu is a figure of 8 type so has no earth/ground,would it be better to mod it with a clover leaf type with an earth?
Gyro:
You may want to check continuity of the screen connection between the 3.5mm jack barrel and the RAC skirts, and also tightness of the RCA skirt contacts. The screen connection should ensure that the Laptop ground and your audio input. At one time you could rely on such things but there's so much crap for sale these days... There should be no (normally) measurable screen connection resistance.
m3vuv:
they seem ok,it only does it when the lappy is running from the mains,its ok just on batterys,i need a fix!
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