|Author:||jazbo8 (registered user: 664 posts )|
|Date:||Tue, Jun 26th, 2012 @ 02:59 ( . )|
I like what you did with the CF bootstrap, I was just reading Merlin's book and he gave the formulas for calculating the gain, so this is a good chance for me to go through the gain calculation exercise (please correct me if I get something wrong or if the result is way off based on your sim)...
A2 = u*(R1+(R2/(1-A1a))/(ra+R1+(R2/(1-A1a)), where
u is the amplification factor of V2
R1, R2 are the anode load resistors
ra is the the anode resistance of V2
A1a is the gain of the CF stage
First, we need to estimate the value for u:
Reading from the chart in the RCA datasheet, we get a gm of 2300 at Vg~-3.4V (from (221-146)/44000*2000),
u = gm*Ra*RL/1000000*(Ra+RL), where RL = R1 + R2,
u = 2300
then we plug in all the numbers, to get the gain for V2:
A2 = u*(R1+(R2/(1-A2))/(ra+R1+(R2/(1-A1a))
A2 = 2300*(22000+(22000/(1-0.95))/(500000+22000+(22000/(1-0.95)))
A2 = 45
So you were right about keeping the gain pretty low for this stage, but this might also be a good place to get more gain if you need it.
--* New prototype amp!
6/26/2012 @ 03:04--jazbo8
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