• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

AC noise filtering

Joined
Feb 20, 2020
Messages
75
Likes
16
Location
Beirut
I've decided to run my computer system off a pure sinewave inverter acting as a double conversion UPS as my AC line voltage fluctuates a lot and I don't want to cause damage to my expensive equipment.

Now the AC waveform is a very clean sinewave as can be seen on my oscilloscope, however the inverter makes an audible high pitched buzzing sound and I'm hearing that exact same sound coming through my studio monitors.

My question is, how do I determine the frequency of this noise and how do I filter it?
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
The ground connection on the PC is still hardwired to mains via the inverter so that problem isn't solved.

The pure sinewave also is not a pure sinewave but probably generated by some pulse density or width modulation + some high pass filtering.
When the base frequency is in the audible range it will not be easy to filter and on top of that may be present as common mode noise opposite the shared safety ground.

You could inform with the manufacturer at which frequency it switches. Chances are there are some inductors making the noise and that may even not be the actual switching frequency.

You need to break the groundloop. Probably the easiest way is to go balanced to the monitors or use line transformers (DI box) in the audio path.
Move the generator out of the room if you can hear it.
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,204
Likes
16,986
Location
Riverview FL
how do I determine the frequency of this noise

Send the noise to analysis software.

REW can tease out the frequencies.

Idle noise measured on an amp here:

index.php
 
Top Bottom