[TowerTalk] Quiet 27" monitors ?????

[Jim Brown]

On 2/15/2022 1:40 PM, James Wolf wrote:
> It seems from observation that much of the noise is generated in the monitor
> power supply.  

Yes. About 20 years ago, a law or other regulation was passed that 
required almost anything that plugs into AC must use a switch-mode PSU 
to reduce power consumption. Unfortunately, this is universally followed 
because they're cheaper to build, but since Part 15 Rules are 
unenforced, it's also cheaper to not worry about the noise they produce.

> Some monitors use an external supply where you can ditch the
> manufacturer's supply and put in an analog DC source.  Typically 19 VDC.

As screens have gotten larger, DC power voltages have risen. I and 
several friends were lucky to buy monitors designed for 14VDC, which run 
fine on 12V batteries.

Some monitors are noisy from circuitry other than the PSU. Especially at 
HF, the noise is conducted to cables connected to them, which act as 
transmitting antennas. In the worst designs, the noise also radiates 
from internal wiring.

FWIW, I never trust any assessments that any given product is quiet, 
because most of us are surrounded by dozens noise sources, both in our 
own homes and those of our neighbors. I use a vintage Kenwood talkie 
that has a receiver that goes down below the AM broadcast band to listen 
right next to a product, and also move along any cables connected to it.

73, Jim K9YC