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Learning about Operational Amplifiers
Trainee Electronics Engineer, currently studying towards my degree in Electronic Engineering at the University of Hudderfsield. Completed my HND in Electrical & Electronic Engineering from Bradford College 2017. Love to try new things and build interesting projects!


November 8, 2015 14:50


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September 24, 2015 00:01

Hi ChelseaBack

A very long time ago I spent a lot of time messing around with op amps. The first ones I touched had about six valves in. They were in an analogue computer donated to my school (John Porte, Etwall, Derbyshire) by Rolls Royce. We only had half of the computer. I think the other half went to a college in Derby which later became the university.

The op amps could be used to sum input voltages. Yes these op amps had a D.C. throughput even with valves. They were all connected to a patch panel. Some of them were connected to Input capacitors so they could perform differentiation and others had feedback capacitors so they could perform integration. Another intriguing device was the Quarter Square Mutiplier (there was only one requiring at least 4 op amps). Anyway that could multiply the input voltages.

All this happened before the invention of integrated circuits but I lived through their invention and was very pleased to get my hands on early chips which had to have small capacitors connected to special pins to keep them stable at high frequencies. Eventually the 748 and 745 chips were invented and by then I was incorporating them in D.C coupled HiFi amps. I've still got a selection of op amps from those days in my shed. They were very useful when my son and two class mates studied electronics at school and required extra tuition from me when their teacher was not available prior to exams.

So perhaps you will connect your op amp as a differentiator and an integrator. The latter is hard to deal with because it's difficult to maintain stability at 0Hz (D.C.) due to a good op amp's high gain. You may have to have some high value feedback resistor regardless and a very finely tuned variable resistor to bias the D.C. input voltage on the differential input. You may need to arrange a course control and a fine control using variable resistors that maintain their setting well (not noisy).

With more op amps you could move onto the quarter square multiplier. See

Good luck and happy learning.

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