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)
20
votes
2answers
469 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 ...
14
votes
6answers
2k 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 ...
14
votes
5answers
3k 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LM394 is obsolete.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 ...
13
votes
3answers
2k 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 ...
10
votes
6answers
306 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 ...
9
votes
4answers
737 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 ...
9
votes
4answers
410 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 ...
8
votes
6answers
884 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 ...
8
votes
6answers
3k 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 ...
8
votes
3answers
423 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 ...
8
votes
3answers
498 views
Simple Adaptive Amplifier Options for Sensor Interfaces
Related: High Resolution ADC for Noisy Sensors in Variable Conditions
I'm building an interface using resistive textile-based sensors that may have different resistance ranges depending on ...
8
votes
4answers
174 views
Flow of holes in transistor?
Bipolar transistor are said to have both electron and holes flow. Movement of electrons can be understood but holes are fixed part of the atomic/crystal structure.How can we characterize their ...
7
votes
8answers
593 views
Does a radio station main amplifier work at the speed of light?
I'm having an argument with a classmate and we can't agree.
He tells me that it's not possible for the amplifier of a radio station to amplify the input signal "instantaneously" (at the speed of ...
7
votes
3answers
591 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 ...
7
votes
1answer
971 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?
7
votes
5answers
5k 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.
...
6
votes
3answers
2k views
Scale 30-50mv signal to 0-5v range
I have a CO2 sensor that output signal values 30mV-50mV. I need to translate these voltages to 0-5V for my microcontroller with the highest resolution. I understand that I can amp the voltage using ...
6
votes
4answers
570 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 ...
6
votes
3answers
1k 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 ...
6
votes
3answers
424 views
Controlling a current with another - home-made alternatives to the transistor?
I have a very basic understanding of how a BJT or a FET works, but I think I got the idea. They are awesome in all regards, except one: you can't make one at home without hot ovens and scary ...
6
votes
2answers
299 views
Can the transformer from an SMPS be used for step-up?
Problem: Stepping up voltage of a high frequency sine wave = 50 KHz to 100 KHz range.
Inside SMPS circuits I find a donut shaped transformer that I think is used to step down the voltage from the ...
6
votes
2answers
156 views
Grounding Shielded Panel-Mount Connectors
I'm building an amplifier in a conductive metal chassis. The general grounding plan is to have an audio ground, a power ground, and a digital ground that converge at a single point on the chassis. ...
6
votes
2answers
248 views
Why would a Diff Amp require both inputs to have a DC path to GND to work?
I'm looking at using a NI PXI-6255 DAQ card and I noticed in the manual it says "Both inputs of the (diff amp) require a DC path to ground in order for the (diff amp) to work."
Is this a common ...
6
votes
2answers
384 views
What's a reference text on analog design?
I'm looking for a intermediate text that covers (discrete) amplifier circuit theory using BJTs and FETs and circuit elements such as current mirrors, differential stages, feedback theory, etc. My ...
6
votes
1answer
213 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 ...
6
votes
3answers
1k 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 ...
6
votes
1answer
416 views
Driving LM3886 at 100 KHZ in Bridge Tied Load (BTL) configuration?
Would someone have experience with driving a pair of LM3886 Overture Power Amplifiers in BTL with up to 100 KHz sine wave?
My parameters:
Frequency band of interest: 20KHz to 100 KHz, sine wave
...
5
votes
3answers
2k views
Why the resistor in this op-amp circuit?
Here's a circuit diagram for a signal response test circuit from the spec sheet for a HA-5195 op amp and looks like a non-inverting amplifier circuit with a gain of 5, plus the 200Ω resistor between ...
5
votes
2answers
1k 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.
...
5
votes
1answer
1k 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?
5
votes
3answers
639 views
Electret Microphone preamplification - will it work for dynamic type microphone?
I'd like to use this diagram to pre-amplify a microphone signal in order to activate the analog input of my arduino
Will it work with a dynamic microphone in place of an electret microphone?
5
votes
4answers
627 views
building an audio amplifier for 2.5 ohm speakers
I recently dug out of my box o' stuff a pair of seemingly decent 2.5ohm bookshelf speakers. I wired them to an old mp3 player I have and while they sound good at low volumes, I get lots of distortion ...
5
votes
3answers
160 views
Dead or alive: Operational transconductance amplifier
My first experience ever with an operational amplifier was with an LM3900 from a Philips experiments kit and these kits date from a long way back in time, when I was a young boy in primary school.
I ...
5
votes
2answers
193 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, ...
5
votes
2answers
534 views
Choosing output filter inductors for switching power amplifiers
Class D PWM switching power amplifiers use an LC filter at the output to filter out the switching harmonics:
Other than the inductance value, what properties are important for this inductor? What ...
5
votes
4answers
532 views
Can I use a PNP Transistor with an Electret Microphone to get an non-inverting output for my Arduino?
I'm looking to simply read the generic sound level from an Electret Microphone. I've seen a number of schematics with NPN transistors, that will provide an inverted output (~5V when quiet, ~0V when ...
5
votes
1answer
355 views
Charging two lead-acid batteries connected in series, separately (with two solar panels)
I have two lead-acid batteries connected in series to produce 24V. They are powering an audio amplifier.
I'd like to be able to charge them while they are powering the amplifier, with solar panels.
...
5
votes
1answer
116 views
What is loading effect?
I have come across this term many times while studying amplifiers. How does this effect affect an amplifier circuit(or any other circuit in which it plays a role) and why is the input impedance kept ...
4
votes
3answers
148 views
For what reason(s) is it not desirable to have the amplifier gain depend on the β of the transistor.
For what reason(s) is it not desirable to have the amplifier gain depend on the β of the transistor.
4
votes
2answers
555 views
What transistor should I use to power a motor from an xbee
I have a small motor what operates at 3.3V at 50mA (sorry no documentation) and a Xbee radio which outputs 1mW.
I would like to allow the Digital I/O pins output on the Xbee to drive the motor ...
4
votes
3answers
443 views
How are RF signals amplified?
So this may be a terribly stupid question but since my RF knowledge is fairly limited I'm asking it anyway. Let's say you have an AM signal that's 5Vp-p at some frequency. To amplify this can you ...
4
votes
5answers
379 views
Troubleshooting a broken speaker system
First I apologize if this is the wrong place for this question.
Recently my sub-woofer/amplifier stopped working, and I would like to know what is broken. I opened the case and didn't find any ...
4
votes
1answer
173 views
amplifier capacitors
Why is that when I use electrolytic capacitors (the one which is cylindrical), when i measure the one end with respect to ground, there is some dc voltage appearing (where in fact it should be 0 volts ...
4
votes
3answers
572 views
HUGE capacitor recommended in datasheet for Audio Amp
I'm using the TPA3111 audio amplifier in a circuit of mine and I'm working on adding the appropriate capacitors. However, on page 18/19 of the datasheet TI recommends to use a 220mF capacitor on the ...
4
votes
3answers
244 views
simple audio amplifier
I did this circuit in my protoboard, and it worked for a while, but the quality sound was terrible, and suddenly it stoped working. Can anyone explain me in which part of the circuit i did something ...
4
votes
2answers
81 views
Single Pole Amplifier
My text book says, "Single Pole amplifiers are always stable,hardly surprising, because in the worst case it can never go beyond 90 degrees."
But it did surprise me and I cannot figure out why a ...
4
votes
2answers
434 views
How do I use a clipping Zener at the input of an Opamp inverting amplifier?
I have a \$ V_{in} \$ signal for which I cannot guaranty that it would have an upper limit. I want to clip this input signal to a limit (e.g.; 8.2V) with a circuit like above.
Is this circuit ...
4
votes
2answers
2k views
Difference between cascade and cascode?
What is the difference between cascode amplifier configuration and cascade amplifier configuration?
4
votes
3answers
387 views
Can someone explain this tube amplifier circuit for me?
I have a tube radio that has really low output (I mean the sound is barely audible at full volume). Probably some capacitor in the LF amp failed. However, after I downloaded the schematic diagram, I ...
4
votes
2answers
544 views
100W Low Pass Filter
Currently I have a 60W amplifier for the 400-500MHZ band with a 50Ω impedance. In order to prevent jamming other frequencies I will need a low pass filter to block any frequencies above 500MHZ. I just ...
