Questions tagged [class-a]

For questions about class A amplifiers, in which the active element conducts all of the time. Other amplifier classes include B, AB, and C-H. Compared to other amplifier classes, class A amplifiers are the simplest and have no crossover distortion, but are the least efficient. Consider using this tag in conjunction with the "transistors" tag.

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Why is emitter voltage changing when input signal is applied in CE amplifier?

When there is no input signal the emitter is at the bias quiescent voltage \$V_E\$. I thought this would be the average emitter voltage even when the input signal is applied.(Because the input ...
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1 vote
3 answers
176 views

Discrete headphone amplifier output stage

What is the role of R13? I tried simulating this circuit using the Falstad simulator and removing it changed nothing. It is a circuit from Small Signal Audio Design by Douglas Self, second edition.
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Why is there a minimum current in a class-a chopper?

$$i_o(t) = {{{V - E} \over {R}} \cdot (1-e^{-{R \over L}\cdot t}) + I_{min} \cdot {e^{-{R \over L}\cdot t}}}$$ Where is the minimum current from, and why are we dividing by R? This is the link https:/...
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92 views

Class A amplifier efficiency

I am trying to simulate this class A amplifier using Multisim. I need help to measure the power loss and then calculate the efficiency. I don't have to calculate the power loss; I could just use ...
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1 answer
116 views

How to decrease clipping in emitter follower

I have a small headphone amplifier with an class A output stage and some negative feedback. The result is not good, but the point is purely self-educational. The part are all jelly-beans and certainly ...
2 votes
1 answer
619 views

Why do I have clipping in this emitter follower

I am trying to design a class A amplifier buffer stage (I know it is not efficient.) I am starting from the simple emitter follower and the next step is to replace the RE resistor with a current ...
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1 answer
130 views

Complementary pair - Role of capacitor on emitter

I bought this little kit for a class AB amplifier. The second stage is quite clear (and typical), but I am struggling to understand the role of capacitor C2 on the emitter branch in the first stage. ...
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6 votes
3 answers
1k views

Cascading common emitter and common collector

I am trying to design an amplifier for a 1 W 8 ohm speaker for educational purposes. The idea is to start from a common emitter amplifier to amplify voltage and then add a common collector (emitter ...
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1 answer
59 views

Kirchoffs Laws and Class-A Amplifier Circuit

I have been attemtping to use Kirchoffs laws to solve a Class A amplifier circuit containing a single transistor. I made several attempts at this trying slightly different approaches. I summarized the ...
1 vote
1 answer
201 views

Designing simple class a amplifier using mosfet

I'm trying to build a simple class a amplifier using a mosfet. I have read few articles about how to do it, but I'm just confused now. I'm not sure how to select resistor values. The articles I've ...
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2 answers
119 views

Class A Emitter follower instantaneous power

I don't quite understand the explanation given in the book I'm reading. Why the maximum instantaneous power dissipated by Q1 is P=2Vcc*I at RL open? Also, why is the current ic1 constant I? Wouldn't ...
2 votes
1 answer
122 views

Emitter-Follower Class A amplifier

I was trying to solve a problem from SEDRA-SMITH book. I got stuck so I refer to the solution. When Studying how the author solved the problem I got even more confused. Let's refer first to the given ...
5 votes
3 answers
585 views

Low power tube headphone amplifier design

I have never worked or even listened to tubes/valves before, so its about time I did. I wanted a simple design to work with being my first tube project, and have found this from diyaudioprojects.com: ...
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1 answer
471 views

Transformer Coupled Class A Power Amplifier

I have seen in some books, in the transformer-coupled Class A amplifiers The transformer is connected between the collector and the VCC. The transformer is connected between the emitter and GND (...
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239 views

Audio amplifier output bypass capacitor

I'm currently designing a single rail power supply audio amplifier and just wondering what the benifits are (if any) and if its worth including a film/poly capacitor in parallel with the large ...
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4 answers
914 views

Single Supply Class-A-Amplifier circuit to amplify voltage signal alternating around ground

I have a sensor which outputs a voltage signal alternating a few millivolts around zero volts and want to design a circuit which prepares this signal for processing by a microcontroller like in the ...
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5 votes
1 answer
412 views

Presence of Crossover Distortion in Class A Amplifier

This question is about theory facts of class A audio amplifier. It is known that class A amplifier is usually biased so that an amplifier's quiescent point is in the middle of the amplifying device's ...
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1 answer
458 views

Class A amplifier with preamp design

I am currently working on a class A audio amplifier designed to work with line in voltage (about -400mv to +400mv). I plan on using an IRFP240 for the mosfet but am undecided on the transistor stage. ...
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2 votes
4 answers
2k views

Class A amplifier - Transistor Q-Point calculation

Reference: http://www.learningaboutelectronics.com/Articles/How-to-find-the-q-point-of-a-transistor-circuit I am trying to understand this q-point calculation. I recently asked a question about the ...
3 votes
4 answers
1k views

Class A Amplifier Design: Emitter Resistance Voltage Drop

I am trying to understand the design principles of Class A amplifiers, primarily for audio purposes. I have read several times that "the voltage drop across the emitter resistor should be in the ...
1 vote
1 answer
729 views

Calculation of DC power drawn by circuit in Class A power amplifier

simulate this circuit – Schematic created using CircuitLab I'm watching Prof. D.C. Dube's lecture (timestamp included) on power amplifiers, and I'm confused about the calculation of DC power \$...
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0 votes
1 answer
104 views

How to design a simple current based class A amplifier

Very much along the lines of Class A single transistor amplifier with 2N3904, but with a current signal input. My circuit is a Zener noise source using the simplest of components. Traditional class ...
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-2 votes
1 answer
680 views

Why does my amplifier turn sine waves into square waves? [closed]

All photos, schematics and the ltspice simulation file are in the folder. https://drive.google.com/folderview?id=1N1yKGnoWQoaGsuHla0DwJwF36_21ZBgX Hello! I have made a simple class A amplifier, but ...
6 votes
2 answers
825 views

How to keep current from draining out the bottom of this push-pull amplifier?

In an earlier question I asked about driving a speaker with a BJT transistor. @Jonk offered a push-pull amplifier design of his own, and @G36 noted its similarity to the JLH amplifier described in a ...
2 votes
1 answer
370 views

Class A Audio Amplifier

I am trying to design a Class A Audio Amplifier with the following specs: 9V DC Power Supply, Maximum withdrawn current 15mA Used with a Low Impedance (8 Ohm) Speaker Provide a minimum variable gain ...
6 votes
4 answers
3k views

BJT base connected to ground and still operates?

When in university I used to get confused how a transistor (NPN) can draw current from ground. I'm now studying power amplifiers and again, this same configuration appears. How does Ir draw current ...
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3 votes
2 answers
6k views

Why can't class A amp drive 8 ohm speaker with just one BJT?

I designed this class A amplifier. It's my first attempt at designing an amplifier with transistors. My objective is to build a guitar amplifier with tubes, but I figured that building an amp with ...
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2 answers
989 views

Can any type of op amp output stage be forced into Class A operation?

I'm trying to choose a good op amp for a Class A small signal audio amplifier circuit. I've done my research and understand the use pull up or pull down resistors externally to force Class A ...
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0 answers
156 views

Simple Class A Output Power Stage of Amplifier

I made this circuit and the output signal wasn't really what I was expecting to be. simulate this circuit – Schematic created using CircuitLab This is class A amplifier (both Q1 and Q2 ...
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1 vote
1 answer
116 views

Balanced Class A Quiescent Current Regulator (OPS of Amplifier)

In my book there is a circuit like the one shown bellow. The author (G. Randy Slone) explains the operation and performance of it but there is still one thing that left me wondering. simulate this ...
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