by Andre Jute <fiultra1@[EMAIL PROTECTED]
>
Apr 22, 2008 at 09:58 AM
On Apr 22, 1:09=A0pm, Ian Thompson-Bell <ruffreco...@[EMAIL PROTECTED]
> wrote:
> I have just been working through the math for shunt derived shunt
> applied NFB around an amp and Ican't get the expected result.
>
> Imagine an inverting amp with an open loop gain of -Ao with a feedback
> resistor from output to input of Rf and an input resistor from signal
> source to the input of Ri. =A0I get a closed loop gain of:
>
> An =3D Ao/(1+(Ri/Rf)+(Ri.Ao/Rf)) when I expected some thing of the form:
>
> An =3D Ao/(1+=DF.Ao) where =DF =3D Ri/Rf
>
> but instead I get Ao/(1+=DF+=DF.Ao)
>
> I have checked the math several times and cannot see where I have gone
> wrong. Anyone throw any light on this?
>
> Cheers
>
> Ian
I can't help you with the math but when you need a break you can get a
giggle at "ZNFB: Religious imperative or manner of speaking?":
http://members.lycos.co.uk/fiultra/KISS%20104%20by%20Andre%20Jute.htm
and at: "Why there is no negative feedback in The KISS Amp"
http://members.lycos.co.uk/fiultra/KISS%20123%20by%20Andre%20Jute.htm
Enjoy.
Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review
