Questions tagged [amplifier]
An amplifier can be used to adapt the range of the signal to a requirement, to make it more robust for transmission, or to satisfy interface requirement (like input/output impedance)
3,964 questions
53
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10answers
10k views
Amplification before tubes and transistors were invented
Telephones are older than vacuum tubes and of course transistors. How was signal amplification done? I mean the technology, not the details. EDIT Some additional informations that I should ...
34
votes
2answers
3k views
What's the difference between field-effect transistors (FETs) marketed as switches vs. amplifiers?
For instance, the J108 JFET is listed as "N-Channel Switch", and the datasheet mentions the RDS on resistance, while the J201 JFET is listed as "N-Channel General Purpose Amplifier" (and the on-...
30
votes
6answers
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Noise reduction strategies in electrophysiology
When recording electrical signals from cells (in a dish or inside a living human or animal body), one major problem is to increase the signal to noise ratio. These signals are usually in the 10uV to ...
29
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2answers
23k views
BJT in Reverse Active Mode of Operation
What will happen if for a BJT transistor, it's emitter terminal is treated as collector and collector as emitter in a common emitter amplifier circuit?
28
votes
10answers
21k views
LM394 is obsolete. What is the new standard log amp circuit?
The traditional logarithmic amplifier circuit is described in National Appnote 311: This circuit uses the difference of two transistor currents to generate the log of the input over a pretty wide ...
25
votes
6answers
5k views
What's the point in a preamp?
I'm talking in the context of guitar amps, but I assume that this question is relevant for any type of audio amplifier. Very often in amplifier schematics I see two stages of amplification -- first, ...
22
votes
5answers
70k views
Why is it desirable in an amplifier to have high input impedance and low output impedance?
I've learned that it's desirable in an ideal amplifier to have high input impedance and low output impedance. Why exactly? What are the implications an amplifier has the opposite- low input impedance ...
22
votes
2answers
8k views
Review request: DIY DC to 50MHz differential oscilloscope probe
Given the cost of proper differential probes, i've decided to make my own. The requirements are: DC to 50 MHz 3db bandwidth A few selectable input voltage ranges, from 3V pk-pk to 300 V pk-pk ...
21
votes
2answers
4k views
What's the purpose of these copper coils with resistors inside them in A Yamaha RX-V396RDS amplifier?
This is an bit of an overly specific question, but I'm curious about the purpose of these coils inside a Yamaha RX-V396RDS amplifier and wondered if anyone could explain what they're for. They appear ...
20
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5answers
13k views
Effect of bootstrapping in amplifier circuit
I am trying to understand this "bootstrap bias" amplifier circuit. The picture below is adapted from the book "Transistor Techniques" by G. J. Ritchie: This circuit is a ...
20
votes
6answers
5k views
I don't quite understand this FET-BJT preamp circuit
I see this circuit a lot on electret microphone preamps, but I don't quite understand it. The FET is operated as a common source amplifier, so it has gain, inverts, and has relatively high output ...
19
votes
6answers
3k views
Does Impedance Matching Imply any Practical RF Transmitter Must Waste >=50% of Energy?
根据to the maximum power transfer theorem, when a fixed source impedance is given, the load impedance must be chosen to match to the source impedance to achieve maximum power transfer. On the ...
18
votes
6answers
24k views
Paper in oil (PIO) capacitors: what is special?
Many audio circuits use PIO capacitors. What are the electrical Characteristics of PIO caps that make them special (i.e. justify the cost)? Which parts of an amplifier circuit benefit most from the ...
18
votes
6answers
64k views
Why is feedback required in op-amp circuits?
I understand that, in order for an op-amp to function correctly, a DC feedback loop from the output to either the inverting or the non-inverting input (depending on the external circuitry) is required....
18
votes
1answer
3k views
OP amps distort sine wave
I am creating a simple circuit in order to amplify the signal from an electret microphone and then add a 2.5V bias to the signal. The problem I'm having is that the signal from the mic is distorted as ...
