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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Need help with audio amplifier design for loud volume

I'm trying to design an audio amplifier. The preamp stage is a voltage divider CE, while the power stage is a Darlington Class A: My goal is to amplify a \$48.7\ \mathrm{mV},\ 1.07\ \mathrm{mA}\$ (...
Halfy's user avatar
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0 votes
1 answer
118 views

Audio Class A amplifier [closed]

Currently I am trying to copy the class A amplifier using the following components: 1k ohms Resistor, 10k ohms resistor, 470 ohms, 50k ohms Resistor, 2n3904 bjt transistor, 10 uF capacitor. With a ...
Brian Perez's user avatar
0 votes
2 answers
131 views

Power Amplifier Class A

I have tried using 2 method but I'm getting different answers in both methods. in the first case I assumed Vce=Vcc/2 and Vcc-IcRc=Vce For maximum power transfer Vcc/(2√2)×Icc/(2√2)=Vcc×Icc/8=20W Vcc/2=...
user avatar
2 votes
3 answers
297 views

Drawbacks of Class A push pull audio power amplifier?

I am willing to develop an Audio power Amplifier myself in a Push Pull configuration of two complementary transistors (NPN,PNP). On the internet, it is found that most of the conventional Class AB ...
CoderBittu's user avatar
4 votes
4 answers
331 views

What went wrong with this class A amplifier design?

I was trying to build a normal class A amplifier, but no matter how hard I try, I cannot find the reason behind my output (blue line) being clipped at the negative cycle of the input (yellow line.) ...
Yeal Takian's user avatar
0 votes
0 answers
73 views

RF amplifier class A

I have simulated a class A RF amplifier. When I simulated the output impedance, it is around 50 Ω for the frequency range that is of interest (50 kHz to 100 MHz), now at the input impedance is around ...
Dimitar Zhekov's user avatar
3 votes
5 answers
468 views

Transistor bias goes negative under input

I am trying to make a simple class A audio amplifier with one transistor (TIP41, NPN) in common emitter configuration as shown in the pictures. The problem I have is that when I add the input signal (...
Alin Paladin's user avatar
1 vote
6 answers
413 views

No voltage gain in a common-emitter class A amplifier using a 3904 NPN transistor - Ngspice simulation

I am currently trying to build an amplifier for a condenser microphone in order to use it as a way to amplify an acoustic guitar. I am having some trouble to achieve my goals. In order to learn I ...
Man789's user avatar
  • 13
0 votes
0 answers
212 views

Gain expansion in class AB power amplifier

Why does gain expansion occur in class AB power amplifier? I can not understand the reason by analysing circuit? Is there any physical reason? Why we can not observe this phenomenon in class A ...
mohammad rezza's user avatar
0 votes
0 answers
45 views

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 ...
across's user avatar
  • 1,130
1 vote
3 answers
545 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.
mrazoun's user avatar
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0 votes
1 answer
188 views

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:/...
Ifiok Ekott's user avatar
0 votes
0 answers
223 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 ...
Frantisek Balaz's user avatar
1 vote
1 answer
194 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 ...
Jonas Daverio's user avatar
2 votes
1 answer
1k 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 ...
Rojj's user avatar
  • 297
0 votes
1 answer
206 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. ...
Rojj's user avatar
  • 297
6 votes
3 answers
3k 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 ...
Rojj's user avatar
  • 297
0 votes
1 answer
71 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 ...
user3728501's user avatar
1 vote
1 answer
410 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 ...
xstmpx's user avatar
  • 155
0 votes
2 answers
231 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 ...
Paumdrdo's user avatar
2 votes
1 answer
240 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 ...
Paumdrdo's user avatar
5 votes
3 answers
827 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: ...
G Frank's user avatar
  • 167
0 votes
1 answer
537 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 (...
Thilina S. Ambagahawaththa's user avatar
0 votes
0 answers
328 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 ...
G Frank's user avatar
  • 167
0 votes
4 answers
1k 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 ...
Amigo54's user avatar
  • 133
5 votes
1 answer
535 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 ...
MucaGinger's user avatar
  • 2,380
0 votes
1 answer
597 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. ...
G Frank's user avatar
  • 167
2 votes
4 answers
3k 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 ...
user3728501's user avatar
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 ...
user3728501's user avatar
1 vote
1 answer
1k 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 \$...
user avatar
0 votes
1 answer
120 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 ...
Paul Uszak's user avatar
  • 7,517
-2 votes
1 answer
1k 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 ...
thegamebusterpl's user avatar
6 votes
2 answers
1k 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 ...
Willis Blackburn's user avatar
2 votes
1 answer
520 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 ...
Amr Mohamed's user avatar
6 votes
4 answers
4k 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 ...
user avatar
3 votes
2 answers
8k 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 ...
Willis Blackburn's user avatar
0 votes
2 answers
1k 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 ...
Samuel Barns's user avatar
0 votes
0 answers
176 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 ...
MucaGinger's user avatar
  • 2,380
1 vote
1 answer
148 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 ...
MucaGinger's user avatar
  • 2,380