An Electrical amplifier when first built has an open loop gain of 120 after a while due to ageing this falls to 90. Calculate the percentage reduction in gain.

An Electrical amplifier when first built has an open loop gain of 120 after a while due to ageing
this falls to 90. Calculate the percentage reduction in gain.
Av (original) = 120, Av (aged) = 90
% reduction = Original gain – New gain x 100%
Original gain
= 120 – 90 x 100
120
= 25%
So the gain has fallen by 25% – not good:
If the same amplifier has 10% of negative feedback applied, calculate the gain with
feedback before and after ageing. Determine the percentage reduction in gain and
comment on the improvement resulting from negative feedback
Application of negative feedback
 = 10% = 0.1
Anfb (original) = 120
1 + (120 x 0.1)
= 120
13
= 9.2
Anfb (aged) = 90
1 + (90 x 0.1)
= 9.0
% reduction = 9.2 – 9 x 100
= 2.17%
So without negative feedback ageing caused a reduction in gain of 25% but with
negative feedback applied the reduction in gain is only 2.17%.
2.2 VERY HIGH GAIN AMPLIFIERS
There are many instances where the open loop gain of an amplifier is very high, i.e.
100,000 in a case like this