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
votes
4answers
667 views
Basic Frequency Control Circuit
How does R4 prevent the output voltage drifting towards one of the supply rails to the op amp? I understand that R4 has to have a high resistance but I do not know why?
Here is the schematic which is ...
20
votes
2answers
510 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 ...
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 ...
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.
...
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?
7
votes
3answers
792 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 ...
5
votes
1answer
377 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.
...
4
votes
1answer
176 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 ...
1
vote
2answers
678 views
Operation Amplifier with Transistor output
Is there a name for feedback amplifier topologies which include an opamp and transistor in the feed-forward path?. I need to design an amplifier with high bandwidth (almost 100 MHz) and high gain (50) ...
-3
votes
1answer
75 views
how do electrons make a metal coil (lightbulb, incandescent, LED, etc.) light up? [closed]
No eBook or tutorial says how thia exactly works. So in practice, I put any 9V battery to a breadboard, connect a resistor and an LED, and it just makes it "go on", but how?
3
votes
3answers
184 views
BJT Bias Design and Operating
I'm to the task to design a BJT Common-Emitter Amplifier with resistance at the emitter as in the figure, and for that I need to:
get the values for \$R_{1}\$, \$R_{2}\$, \$R_{C}\$ and \$R_{E}\$
...
1
vote
1answer
309 views
Impedance for Helmholtz Coil Connected to Audio Amplifier
I am trying to design a Helmholtz coil, that will have an impedance of about 2 ohms (the reason for this being that I am going to hook it up to a audio power amplifier, so to get the same wattage ...
0
votes
3answers
317 views
Role of capacitors in amplifier
What is the significance of a coupling capacitor in a common-emitter amplifier? What would happen if it is removed? What will be the effect on AC amplifier gain on removing it?
16
votes
7answers
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 ...
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 ...
2
votes
3answers
674 views
Picking a DAC for an audio amplfier
I'm trying to use a specific audio amplifier, TPA3111D1, to power a 10 watt speaker from a microcontroller. I would like to generate sound from a microcontroller that doesn't have a built in DAC, so ...
8
votes
3answers
511 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 ...
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 ...
6
votes
1answer
217 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 ...
5
votes
4answers
630 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 ...
-1
votes
1answer
1k views
How to amplify an electret microphone
I need to amplify an electret microphone for use with an Arduino Uno. I have a few capacitors and resistors and several transistors one of which is an N-channel.
Any ideas?
Can you please also provide ...
4
votes
2answers
563 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 ...
3
votes
1answer
158 views
How can I modify this circuit for a higher gain?
Here is an image of an amplifier circuit.
How can I modify this for a 10-50 times more gain. I put a wire from pin 1 to 8, but I didn't get enough gain.
3
votes
2answers
149 views
Is there an amplifier such that the gain is equal to the ratio of two potential differences?
I have been toying with some alternatives to transistors in building logic gates. I am particularly interested in the device I tried to summarize in the title of this post. The chip would have 8 pins:
...
3
votes
1answer
595 views
Testing an Audio Power Amp with Paralleled Transistors
A question concerning my current repair project of an audio amp that uses big (600 W) but otherwise rather classic complementary output stages:
I assume when testing an audio power amp with 6 pairs ...
2
votes
3answers
128 views
Difficulty with Common Emitter Amplifier
I'm trying to take the input from a microphone and use it to power an LED, so that it's off at ambient sound, and (the peak brightness) gets brighter with noise level. It's okay if it flickers, I'm ...
2
votes
2answers
201 views
technology to search small objects like pendrive, key-chains etc
I am a web developer by profession. few days back I lost 8gb pen-drive :( I don't it is in home or somewhere else.... So now I am thinking of a device which can be attached with small objects so that ...
2
votes
2answers
205 views
lower Vcc of power amplifier and still provide 30 watts
Above circuit is a power amplifier delivering roughly 30 watts in the 4 ohm load (assuming its a speaker). 11 times 3 is around 30 watts. When we look at Vcc, it looks huge when compared to ...
2
votes
4answers
250 views
amplifier quality waveform for different transistors
I have tested two transistors in multisim, the first is the default(more of generic) and the second is the 2N3904
here is the first picture with default transistor in placed
and here is the ...
2
votes
2answers
324 views
Humming and Transmission issues
First of all, I am going through designing all of this because I did not find a ready made circuitry for my purpose which is mentioned later. If you know a circuitry that is well tested and does what ...
2
votes
1answer
470 views
Amplifying signal from CO2 Sensor
I am trying to amplify a MG811 CO2 sensor to a range readable by an ATMEGA2560 (0-5v). I have other analog sensors, so do not want to change ref voltage on Atmega. I have found a module that scales ...
1
vote
3answers
160 views
signal clipped despite q point is middle
Why is that the output signal is clipped despite the fact that the transistor's q point is located halfway of Vcc???
here is the schematic
and clipping here
From my analysis, as you can see, ...
1
vote
2answers
320 views
detecting low signal levels with a transistor
This question made me wonder. Say I want to drive a LED when a small level audio signal is present. I understand how to do this with an opamp, but how about a transistor. You'd have to bias it so that ...
1
vote
2answers
125 views
Flipping a signal
I've an input of two input lines, one being connected to ground and one carrying the signal (measured to ground). The output should be three lines with one being ground and the others measured in ...
0
votes
1answer
211 views
Help in designing a speaker driven by an LM386
I'm trying to design a circuit which produces a 17KHz pure sine wave from a speaker using the following components:
PIC16F1783 (microcontroller with DAC)
an LM386 amplifier and an 8-Ohm 1W speaker.
...
-1
votes
3answers
327 views
Calculating the power of a simple amplifier
I found this circuit on internet. It says it's a 1w amplifier. There is no explanation about how that is calculated. How could the power of this circuit calcuted? (input is a radio)
And is there any ...
-2
votes
0answers
69 views
Basic audio amplifer circuit with transistors [duplicate]
Possible Duplicate:
Simple Audio amplifier Using Transistors
I'm looking for a basic audio amplifier(1w - 0.5w) circuit which is designed with transistors. Could you help about that?
-3
votes
2answers
300 views
class AB power amplifier
i impelemented a class AB amplifier
As you can see, my Vcc is only 1 Volt, the question is, how come i can still make 2.8 Ampere supply to the 4 ohm speaker/load? Is it a bug in MultiSim, or did ...
