Topic 39: Multi-Stage Amplifier Analysis

In this video we analyze a three-stage, capacitively coupled amplifier made from discrete transistors. The advantages and disadvantages of capacitive coupled, class-A designs are highlighted in this analysis. Although we do obtain some pretty impressive gain values with this design, the output voltage swing, and maximum output power are not very good.

[@bob_mosavo]

Thanks 👍

[@jakep8484]

I would try to use as few coupling caps and would add emitter resistors on the finals.

[@Electronics4Guitar]

I agree. But I haven’t covered direct coupling in the tutorials yet. This amplifier was designed as an exercise in the analysis of capacitively coupled circuits. And it demonstrates the problems with using capacitively coupled, class-A amplifiers when large signal swings are desired. I’ll get to direct coupling soon.

[@heidicoren4054]

Thank you for good explanation

[@Electronics4Guitar]

Glad it was helpful!

[@AnalogDude_]

Why would you do all this trouble and not get a nice NE5534 or OPA1677 to connect this to the push pull setup or C4?
Feedback from the push pull output to the inverted input of the opamp and your crossover distortion should be solved not using the diodes, like the push pull circuit from the known encyclopedia. tried it in the sim, turning this opamp to voltage
follower and the zero cross distortion returns, I have also drawn a Sziklai push pull from thin air, but now i learned about R12, R13, C6, C7.
I just used 1M to pull up / down for R10, R11 to the bases to force them transistor closed.
The Falstad sim shows it works fine.

[@Electronics4Guitar]

I’ll put the transistors in the feedback loop after I cover that concept in the context of op amps. And I’ll show why that isn’t necessarily the panacea that it would appear to be. There’s a method to my madness. All in good time.

[@AnalogDude_]

@@Electronics4Guitar Ya, using transistors may add some unique sound flavor, but i wanna make something to replace my 5€ pc speakers.

[@Electronics4Guitar]

I hear ya 👍🏻

[@victimovtalent6036]

R Th is R thevenin?

[@victimovtalent6036]

@@Electronics4Guitar can we use symetrical power supply for this circuit design?

[@Electronics4Guitar]

@@victimovtalent6036definitely. The output stage could be operated from a bipolar supply with no modification (you could eliminate the output coupling cap). The two driver stages would need to be redesigned though and would still require capacitive coupling.

[@Electronics4Guitar]

@victimovtalent6036 yes, it’s the Thevenin equivalent resistance. I should have noted this.

[@victimovtalent6036]

@@Electronics4Guitar thank you for your explanation,i'm very appreciate👍🙂