Noiseless Biasing, 470k or 4.7M series resistor?

matt239 · Post by **matt239** » 18 Sep 2011, 05:05

I've seen R.G.'s noiseless biasing described as using a 470k or a 4.7M series resistor after the 10k/10k voltage divider. Which is it?
How does the value of this resistor affect impedance? How is this calculated??
Thanks, all.

Ihunda · Post by **Ihunda** » 25 Sep 2011, 18:37

Bumping the thread, I'd really like to understand why this creates less noice!

merlinb · Post by **merlinb** » 25 Sep 2011, 21:28

http://www.geofex.com/Article_Folders/m ... dmuamp.htm

With the stock arrangement half the power supply noise is fed to the base of the upper transistor, and is passed to the audio output.
With the 'noiseless' arrangement the PSU noise is decoupled to ground. R.G also mentions Johnson noise and excess noise, but they are negligible in this situation, with either arrangement.