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Op-Amps

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Printed Date: 27 Mar 2026 at 2:55am
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Topic: Op-Amps

Posted By: Graham Slee
Subject: Op-Amps
Date Posted: 28 Feb 2023 at 8:55am

An op-amp is a selection of semiconductors that perform a mathematical task within particular limits, that is integrated as a (sub) circuit onto a small piece of purified silicon using etching and depositing of other substances, using a lithographic process.

The earliest op-amps were individual components on a printed circuit board, which were basically plug-in modules using an edge connector.

Basically, they are ultra high gain amplifiers with two inputs and an output. The inputs are differential so that the resulting output is the sum of the difference between the inputs.

An audio op-amp is an op-amp designed to suit audio applications, again within particular limits. Because the output will do whatever is required to make both inputs equal it can be used for amplification of small signals, using it as a feedback amplifier.

An op-amp cannot work on its own and requires other circuitry to make it work as required. It can only do what its external circuitry allows it to do.

The characteristics of the op-amp dictate the limits as to what it can do, and the external circuitry must respect those limits, or the op-amp will misfunction.

Sometimes the problems found in discrete audio circuits can be overcome much more easily by substituting that part of the circuitry with an op-amp, but the op-amp might impose its limits on the intention of the designer.

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That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps

Replies:

Posted By: Graham Slee
Date Posted: 01 Mar 2023 at 1:54am

This book...

https://www.analog.com/en/education/education-library/op-amp-applications-handbook.html - https://www.analog.com/en/education/education-library/op-amp-applications-handbook.html

...is free of charge in PDF form, although if you search for it you'll simply get ads of places to buy it.

In this book, you will realise that an op-amp is a block containing transistors and maybe the odd diode or zener diode, and perhaps a j-fet input stage and some tiny monolithic capacitors.

I'm often asked what is the difference between op-amps and discrete circuitry. The answer is that an op-amp contains discrete circuitry of a predetermined nature, but etched on a chip!

Transistors were pence and op-amps were tens of pence.

Just because an op-amp cost 50 pence, didn't mean it was inferior to 20 discrete transistors doing the same or similar job (at 2.5 pence each...)

Those believing the trash written in magazines are obviously gullible.

The value of a circuit is in its implementation. Some on here know me for the "smooth sound" (of the good variety that is), and so it should come as no surprise to read on a sales site that the CCM3 mixer from 1992 had a "smooth sound", seeing I designed it. I'll not go into how Audionics used to ensure its designer remained a poor nobody, but they're bust now and I never shed a tear for them.

So, it's how an op-amp is applied, nothing to do with op-amps being better, or worse than discretes.

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That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps

Posted By: Sylvain
Date Posted: 01 Mar 2023 at 10:12am

My gratitude for the Education Library reference. O

Op-Amp are very prominent in Audio circuit performing multiple defined tasks and shorten circuits boards. National Panasonic and Burr Brown(Texas Instruments) and Analogue devices have evolved to optimise Audio circuits and resistors and capacitors even in SMD forms are almost obsolete.

Posted By: peterb
Date Posted: 01 Mar 2023 at 5:18pm

in 2012 Elektor published a PreAmp and Tone Control design by Douglas Self which used all Op amps (a lot!) except for 4 transistors in the MC stage. I was tempted to make it as the figures looked good, but never did so can't say if the sound matched the specs. If anybody want a copy of the 3 Pdfs please message me.

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Peter
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Dual 505-1, Cyrus CD T, DIY 80W MosFet amp and PreAmp, 2xKEF 103.2

Posted By: Fatmangolf
Date Posted: 01 Mar 2023 at 7:44pm

Thanks from me too Graham. Like Peter I have got clippings from old electronics magazines with lots of op amps...

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Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.

Posted By: RichW
Date Posted: 02 Mar 2023 at 9:17am

Thanks Graham.

Will try to follow the information on op amps in the link you provided.

I remember very little now from the Polytechnic electronics course from many years ago.
Ideal op amp characteristic of 'infinite' open loop gain - both inputs could be assumed to be
at the 'same' voltage when in circuit, high input impedance and 'zero' output impedance.