Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [preamp]

A preamp takes in very weak DC voltages or audio or RF signals and amplifies them enough to be used by a more conventional amplifier. Input may be in microvolts and output maybe 1 volt RMS or peak. They are often specific to amplify DC, LF/audio, RF or microwave bands. No preamp can cover DC to microwave bands and have good parameters at both DC and RF without software offset and gain correction.

191 questions
25
votes
7 answers

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, the signal is amplified a smaller amount by a…
Jacob Garby
  • 714
  • 9
  • 18
17
votes
3 answers

Why does this op amp stop working after some time?

I have an audio streaming device I bought that has analog audio output that is way too low (it’s supposedly line level, and I’m not the only one who’s complained about this). I’ve been using this as an excuse to learn about TOSLINK and DACs, but…
nsayer
  • 1,543
  • 1
  • 18
  • 35
14
votes
1 answer

Why is there a winding on a capacitor?

I just came across this tube RIAA preamp on which there is a coil on the input capacitor, can someone please explain what's the reason of such thing? The schematic and the actual circuit bellow. The site with the full circuit and details is:…
Gabriel Santos
  • 417
  • 3
  • 12
8
votes
5 answers

Electret microphone: selecting a bias resistor

I have inherited a circuit from a colleague using a MAX4063 pre-amplifier and an electret microphone. It's almost identical to figure 4 from the preamp datasheet: But where that circuit has 2× 1 kΩ resistors in series, I have just one. I'm not…
pjc50
  • 46,540
  • 4
  • 64
  • 126
7
votes
3 answers

Purpose of these two transistors

Hi does anybody know what's the purpose of the Q1 and Q2 transistors, sounds to me like they are constant current sources. Am I wrong? Could somebody explain me the purpose of those Q1 and Q2 transistor configuration there? Note, This is a simple…
Standard Sandun
  • 1,695
  • 2
  • 23
  • 38
7
votes
4 answers

How does a preamplifier improve the Signal-to-Noise Ratio (SNR)?

I'm trying to understand how a preamplifier works. Is the noise not amplified the same amount as the signal? If so, how is that done in the preamplifier?
physicsnoob1000
  • 171
  • 1
  • 2
6
votes
1 answer

Electret Microphone Preamp Circuit

The following electret microphone preamp circuit seems to work pretty well. My electret model is a little off because on the bread board R6 needs to be ~33k to get the output at 1/2 supply. Just a little explaination: The current mirrors provide a…
squarewav
  • 1,440
  • 1
  • 14
  • 33
6
votes
3 answers

What is the purpose of these passives in a microphone pre-amplifier circuit?

This is the typical application circuit of the MAX4466 "microphone preamplifier" op-amp. Are these resistors/capacitors purely for generating a bias voltage? If so, aren't there much simpler ways to do this, like a simple voltage divider? Are they…
laust0rm
  • 81
  • 7
6
votes
1 answer

Designing 2-stage BJT CE class-A voltage pre-amplifier with specified goals and without global NFB

BJT CE Class-A Voltage Pre-Amplifier Suppose a design requirement limits the selection choices to the following class-A BJT common emitter stage topologies. No global NFB is permitted. Only local NFB via the emitter leg with passive components as…
jonk
  • 77,059
  • 6
  • 73
  • 185
6
votes
2 answers

What is simpliest possible guitar active preamp design

I want to build guitar active preamp inside my bass guitar. It has 2 humbacker pickups (3.4kOhm DC resistance each) for 2 lower and for 2 upper strings, and i want to preamplify each with a separate preamp, so i choose TL072. Let's look at just one…
user149105
6
votes
3 answers

Piezo transducer preamp and AGC/compressor

I've been suggested this circuit as a good low-noise high gain piezoelectric transducer preamp (used to pick up really faint sounds in water). It is nice because it includes a high pass filter (yet no AGC or a compressor, which would be useful for…
Allison Ross
  • 61
  • 1
6
votes
4 answers

ESD protection for OpAmp inputs and outputs

The following circuit is a preamplifier that we are currently using. In real practice, we do not have the photodiode connecting with OpAmp directly on board. Instead, the photodiode is connected with the OpAmp through a connector. The input and…
richieqianle
  • 1,612
  • 3
  • 24
  • 44
5
votes
1 answer

Capacitor values for non-Inverting op-amp circuit

I found the following schematic here and built it to test it . . . I think all the capacitors are there to just block DC, but how important are the capacitance values and how does one determine the value of Co? The source webpage only discusses…
learnvst
  • 1,213
  • 3
  • 21
  • 28
5
votes
3 answers

Best microphone picking up sound within a small room?

I've tried several Electret Condenser Microphones as input to a generic USB audio sound card: MO064202-4 MO064402-4 MO064402-5 All mics work great at close range (about 1 or 2 inches). However, none of them would pick up any sound at ranges further…
Hari Wiguna
  • 93
  • 1
  • 8
4
votes
3 answers

Name and cause for phenomenon in microphone preamp output as seen on scope screen

What might cause 1 kHz sinusoidal signal to change such as seen on the screen? How is this phenomenon possibly called? I have quite a lot of hand microphones with built-in opamp preamp and electret microphone. Some of them function ok and give ideal…
UIR
  • 63
  • 4
1
2 3
…
12 13