We’re rewarding the question askers & reputations are being recalculated! Read more.

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)

Filter by
Sorted by
Tagged with
50
votes
10answers
9k 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-...
29
votes
6answers
12k views

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 ...
26
votes
10answers
17k 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LM394 is obsolete.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 ...
24
votes
6answers
4k 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, ...
24
votes
2answers
19k 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?
20
votes
5answers
64k 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 ...
20
votes
2answers
3k 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 ...
19
votes
5answers
4k 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 ...
18
votes
6answers
20k 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
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 ...
18
votes
2answers
4k 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 ...
18
votes
2answers
1k views

AB Without Diodes

Looking at another question about an AB Amplifier stage the answer was the classic diode biased push-pull stage like this... which I voted up like others.. simulate this circuit – Schematic ...
17
votes
6answers
58k 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....
17
votes
2answers
302 views

How to find the problem of this old Marantz amplifier?

After a first question referring to resistor symbols, I'm back with this old Marantz PM-68 class AB amplifier and I will refer to components using their ID that can be found in the service manual. ...
16
votes
6answers
2k views

Does Impedance Matching Imply any Practical RF Transmitter Must Waste >=50% of Energy?

According 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 ...
16
votes
4answers
5k views

Can a power MOSFET for switching application be used as a linear amplifier?

Power MOSFETs nowadays are ubiquitous and fairly cheap also at retail. In most datasheet I saw power MOSFETs are rated for switching, without mentioning any kind of linear applications. I'd like to ...
16
votes
5answers
60k views

Simple Audio amplifier Using Transistors

I would like to build a simple audio amplifier using transistors. I know there are IC designs specifically for the task. But i want to use transistors so i can learn how to use them for amplification. ...
14
votes
2answers
38k views

What wattage should a headphone amp be?

I was at a local surplus store today and I got two LM386N ICs. I thought I could make a really simple headphone amp out of these. But I have no idea what the wattage of a normal headphone amp is. ...
13
votes
4answers
2k views

Why put a step-down transformer after a vacuum tube in an a valve amplifier?

I'm researching valve amplifiers. I found this schematic for one: So the input is amplified by the first valve, and then the amplified signal is amplified again by the second valve, right? My ...
13
votes
4answers
6k views

Alternatives to transistors

I'm trying to think of alternatives to transistors, simply because I'm curious. I don't care so much about the amplifying characteristics of transistors as their ability to make logic gates. Here's ...
13
votes
6answers
1k views

Amp measures board twist (unfortunately!)

Well, this is a toughie -- though fairly simple. Does anyone have experience with board twist affecting your circuit? We have a board design that is supposed to measure a loadcell. We have finally ...
13
votes
3answers
45k views

Scale 30-50 mV signal to 0-5 V range

I have a CO2 sensor that output signal values 30-50 mV. I need to translate these voltages to 0-5 V for my microcontroller with the highest resolution. I understand that I can amplify the ...
13
votes
3answers
12k views

What is a PA/LNA?

I saw a comparison of two similar radio receiver modules. They used the same IC, but one had a greater range due to the inclusion of a "PA/LNA" which I understand to be an abbreviation for "Power Amp /...
13
votes
1answer
26k views

Can the Common Emmiter Amplifier use a PNP Transistor instead?

This is a simple Class A amplifier using an NPN transistor: Is there a way this can use a PNP transistor, instead (with only 0V and +Vcc, not 0V and -Vcc)? Why or why not?
13
votes
2answers
1k views

What power limitations was chirped radar designed to overcome?

Chirped Pulse Amplification (CPA) is an optics technique, winner of the 2018 Nobel Prize in physics, which is used for producing short laser pulses at intensities which are high enough that the gain ...
12
votes
6answers
3k views

Does non-matching impedance of amplifier and speaker distort the sound?

I'm about to buy a pair of headphones and an audio interface with built in amplifier. The specs say that the amp's impedance is "<30 Ohms". The headphone I'd like to buy is a Beyerdynamic DT 990, ...
12
votes
3answers
14k views

How do I get +5v for loud noise, 0v for silence from Electret Microphone (or other components)?

I have been asking a few questions here to get to a proper one, the initial questions I asked are linked to at the end. I used Fritzing to make up some schematics of my initial thoughts, but at the ...
12
votes
4answers
10k 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 variation of the "voltage ...
12
votes
4answers
67k views

What is the definition and purpose of a pre-amplifier?

I find in many places mentions of pre-amplifiers being used to boost audio signals prior to feeding to a power amplifier. Wikipedia's article on pre-amps gives some hints at their usage, but it doesn'...
12
votes
3answers
2k views

Audio Amplifier Op amp

I'm trying to design a circuit in which a microcontroller produces a signal and then using an amplifier drives an 8ohm speaker. I've so far used LM386, but it cannot go above 1W, which turned out to ...
12
votes
2answers
1k views

Is this a current mirror?

I saw this in AN-19 of linear's application notes for a boost converter. It is an error amplifier for a boost converter. I'm not quite sure what the symbol for Q55 and Q56. My best guess is a current ...
12
votes
1answer
3k views

Fully understanding LM386 datasheet minimum parts example

I'd like to fully understand the circuit marked as "Minimum Parts" at page 5 in LM386's datasheet: Is there any reason for 10k resistance at the input potentiometer or is it just an arbitrary value? ...
11
votes
5answers
2k views

Why are two stages used for an instrumentation amplifier?

When we have a two-stage instrumentation amplifier, such as the following. Why do we need the first stage of the two Operational Amplifiers? Couldn't we just input V1 and V2 into the differential ...
11
votes
3answers
5k views

Choose the better values (in terms of range) for resistors in this non-inverting op-amp circuit

These days I'm looking at operational amplifiers; from what I've seen, implementing them in a circuit is quite simple, at least when they are connected as "non-inverting". Determining the gain/...
11
votes
4answers
2k views

Signal Processing with Op Amps

I'm tasked to reproduce the following signal using only Op Amps (and resistors). I'm pretty sure I must add two signals, the square and triangular waveforms, it is just pretty hard to figure out ...
11
votes
4answers
4k views

Is the input impedance of an operational amplifier (op amp) infinite or zero?

Ideally, the input impedance is infinite. But, in calculating the input resistance (Rin) of a difference amplifier, the author took the concept that the two input terminals are short circuited, which ...
11
votes
4answers
67k views

Best transistor to use for audio amplifier

This term, we will be designing an audio amplifier. So far in our lecture, we are still at BJT and based from what I've heard, FETs will just be partly discussed unlike the thorough one on BJT. Anyway,...
11
votes
3answers
7k views

Audio Amplifier PCB Design Tips

I am going to design a stereo audio amplifier with TDA2030A. This is going to be an amplifier that is going to be powered from 27.6V DC and 12W per channel. Is there any sources that I can learn PCB ...
11
votes
5answers
45k views

How are speakers matched with audio amplifiers? (avoiding overloading either)

I know a similar question title has been asked, but I believe that does not answer my question (and I couldn't think of a better way to phrase the question). I'm a bit confused by how exactly an amp ...
11
votes
4answers
4k views

Just how does high VSWR damage RF amplifiers?

Just how is it that a high VSWR can damage the final transistors in an RF power amplifier? Is the transmission line significant beyond the effect it has on transforming the impedance of the load at ...
11
votes
2answers
10k views

Designing a BJT Amplifier given some constraints

I am trying to design a BJT amplifier following this model: Where the beta parameter may vary from 100 to 800, the voltage between the base and the emitter equals 0.6V (active mode), \$V_t = 25 mV\$ ...
10
votes
10answers
37k views

Why is Vbe a constant 0.7 for a transistor in the active region?

I'm going to take an example of a simple common emitter amplifier. Forget about biasing and things for now, but focus on the crux of this circuit. As how I understand it, a voltage between the base ...
10
votes
3answers
871 views

Amplifying High Voltage nA Current

I have a circuit that is essentially just a 1kV DC source connected to a very high resistance (basic circuit outline), within which current in the range from 0.1nA to 500uA flows that I am trying to ...
10
votes
1answer
920 views

Class AB amplifier

What role does Rv play in this AB class amplifier?
10
votes
3answers
2k views

Common Emitter not amplifying

I am trying to make a 27 MHz carrier wave transmitter from a crystal oscillator and a secondary amplifier. Thi is the complete circuit: simulate this circuit – Schematic created using ...
10
votes
3answers
19k views

Input impedance of inverting amplifier clarification

Take a standard inverting amplifier: I'm unclear on what the input impedance is. At first I thought it was the equivalent resistance from the inverting input to the ground, which would be Rin || Rf, ...
10
votes
2answers
2k views

What's the difference between small signal bipolar junction transistors (BJTs) marketed as switches vs. amplifiers?

For instance, the MMBT3904 and MMBT3906 BJTs are listed as NPN/PNP Switching Transistors, and the datasheets mention the switching times, while the BC846 and BC856 BJTs are listed as NPN/PNP general ...
10
votes
3answers
9k views

How can one pair of headphones be connected to two audio sources?

I'd like to connect one pair of headphones to the headphone jack on two audio sources simultaneously. I realize I can't just wire two audio sources in parallel since they'll then be driving each other....
9
votes
2answers
2k views

What property of a BJT transistor makes it an amplifier?

I know how we can amplify a given signal using BJT transistors by biasing them. But I would like to know what is that crux property which enables BJT transistor to act like an amplifier. Is it the ...