Simplest amplifier design with resistor and transistor

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Discussion Overview

The discussion revolves around designing a simple audio amplifier using a resistor and a transistor, specifically for amplifying sound from an iPod to a mono speaker. Participants explore various design considerations, power requirements, and potential configurations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant requests assistance in building a very simple amplifier using minimal components.
  • Another participant questions the power requirements and the type of signal being amplified, noting that "simple" can be subjective and that distortions may arise.
  • A participant suggests that a basic class A amplifier could be a solution but highlights the inefficiency of such designs and the need for more components than just a transistor and resistor.
  • There is a suggestion to use operational amplifiers for a simpler and more effective design.
  • A participant proposes that a simple transistor-resistor setup would be inadequate for audio purposes and recommends a push-pull output stage, mentioning the potential for crossover distortion.
  • Links to various amplifier designs are shared, including a two-transistor amplifier and a darlington pair configuration.
  • One participant inquires about the loudness increase provided by a 1 watt amplifier, leading to a discussion about the decibel scale and power requirements for perceived loudness.

Areas of Agreement / Disagreement

Participants express differing views on what constitutes a "simple" amplifier design and the necessary components for effective amplification. There is no consensus on a single design approach, as various configurations and their implications are debated.

Contextual Notes

Participants mention limitations regarding efficiency, distortion, and the need for additional components beyond a single transistor and resistor. The discussion reflects varying assumptions about the desired outcome and application of the amplifier.

circuit man
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Hi guys,
I need to build a REALLY simple amp for a friend. I only want to use a resistor and a transistor plus the normal stuff(battery and speaker). Please help.

Thanks in advance,
Circuit Man
 
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What are your power requirements? What sort of signal are you amplifying? The term "simple" is a little subjective. How about distortions on the output?

All of these factors will affect the amp design in some way. The design will require more that just a transistor and resistor.
 
I want to amplify a computer speaker (iPod) to a mono speaker not very loud.
 
It sounds like you are planning to build a simple class A amp.
What is the purpose? Is it just a demonstration?

Practical transitor amplifiers tend to be fairly complicated, class A amps are simple in principle but in reality you need more than a single transistor and a resistor to make something that sounds decent.
Also, class A amps are very inefficient so a 9V battery won't very long.

If you want to build something very simple just use an operational amplifer such as LM3875 or something similar. Then you can actually build something that works using a few resistors and a capacitor or two.
 
For your audio purposes, a simple transistor-resistor setup won't cut it. You will at least need a push-pull output stage (needs two transistors). This is a good idea because as f95toli mentions - the single transistor will simply be too wasteful. But the push-pull as some distortion of its own. You'll need to eliminate this crossover distortion; usually by biasing the push-pull with diodes (see dlgoff's link).
Here is a two transistor amp:
http://www.geocities.com/tomzi.geo/2tr_amp/2tr_amp.htm
But this suffers from inefficiency.
 
cool thanks
 
  • #10
How much louder would a 1 watt amplifier make an iPod? It is probably obvious but I don't know
 
  • #11
Are you familiar with the decibel scale?

The rule is as follows: to reproduce a sound twice as loud as the original, the amplifier needs to supply 10 times more power at the output.
Assuming that your ipod has a 30mW output, you get a gain of about 15dB.
 
  • #12
yes, thank you
 

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