Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit 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.

0
votes
1answer
62 views

How to measure the output impedance of a valve preamp?

I was trying to measure the output impedance of a DIY preamp for the past couple of days without any luck. Each time, I got to the same result of around 3K3 ohm, which is unbelievably low. This is ...
0
votes
0answers
56 views

How the oscilloscope input voltage rating is independent from attenuator setting

Since I'm taking part in a quite interesting educational project that incorporates the design and testing of the analog front-end of a relatively high speed ADC (up to 200 MSps) I've been studying the ...
0
votes
0answers
48 views

Power Supply for the Pre-amplifier I bought

I bought this China clone "Marantz-7-M7-Tube-Buffer-Audio-Preamplifier-Pre-AMP-Board-KIT" I thought that it was just simple. I just don't want to throw it away, but what does 220v mean input meant in ...
23
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, ...
0
votes
1answer
86 views

Attempting an audio pre-amplifier circuit with falstad.com

I'm new to electronics and discovered the falstad.com simulator. I wanted to model this audio pre-amplifier circuit: So I went into falstad and drew this: My pre-amplifier circuit on falstad The ...
1
vote
2answers
85 views

SparkFun Sound Detector Circuit Analysis

I would like to request some help in analyzing the op-amp circuit used by SparkFun here. I'm particularly interested in the pre-amplifier portion of this design. The write-up included by SparkFun ...
1
vote
1answer
128 views

How to find feedback resistor value?

I want to implement typical guitar preamp scheme, like following: I see, that it will have input impendance =2.2M...
0
votes
1answer
65 views

Preamp Ground Loop Problem

I have built the blue circuit above for my microphone but the one of the problems I'm facing is that when I connect it to my laptop's audio input, it creates a humming sound. My assumption is there is ...
1
vote
2answers
149 views

Troubleshooting TL071 to TA8207 100 Hertz hum

I worked out to build a pre-amplifier connected to a power driver in a single setups(a pcb). Problem arises when it's powered up. here are a few questions. Setup has a TL071CP as preamp with a unity ...
0
votes
3answers
91 views

Does somebody have a schematic for a stereo electret condenser microphone?

I’m trying to use a Cmoy headphone amp (built around an OPA2227P chip) as a hard-wired in-ear-monitor. I bought a stereo electret condenser microphone from Jaycar this afternoon, but I can’t get any ...
0
votes
1answer
116 views

Modern piezo microphone impedance-matching circuit

I want to record sound with a piezo transducer. I am connecting it to my sound card's input which has a good mic pre-amp. The levels are quite good and the sound seems quite clear but there's a lack ...
2
votes
1answer
148 views

MEMS microphone gain calculation for MCU ADC

I've got a Knowles SPH1642HT5H-1 (pdf link) analog MEMS microphone that I'm planning to connect to one of the ADC inputs on an STM32. I've done what I think are the correct calculations to determine ...
0
votes
2answers
97 views

Built a electret preamp but poor low frequency response

I have built this preamp using the TL071 IC. It works, but it does have a bad low frequency response. If I plug the mic directly to my PC i can hear low frequencies much better. I don't have any ...
0
votes
1answer
112 views

Help with design a mic preamp with opamps for PGA and ADC

I want to sample an audio source using an electret microphone and analyze the spectrum of it with a uC. I'm interested in the 100Hz-2.5kHz range, so I calculate with these values when I tried to ...
3
votes
3answers
124 views

Guitar preamp problems

I built the following preamp to use with guitars Basically the idea is to keep it on a single rail so that I can use it off the same battery with this power amp https://www.eleccircuit.com/bridge-...
4
votes
3answers
269 views

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 ...
0
votes
0answers
86 views

How to outline the signal path of this schematic?

I'm looking for some help finding out the signal path from input to output when the effect/normal switch on the far right is on normal. I couldn't figure out which path the signal takes when the ...
0
votes
3answers
237 views

Phono preamp, one channel doesn't work

I have built a stereo preamp using this circuit (taken from here Hi-Fi Phono Preamp Rod Elliott - ESP), but for some reason I can't get the right channel to work at all while the left one plays. Now ...
6
votes
1answer
293 views

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 ...
0
votes
1answer
59 views

Output Impedance of a Pre-amplifier

This is an AC equivalent circuit of a pre-amplifier. I already derived the formula for input impedance (Zi) but I'm having trouble getting the formula for output impedance (Zo). I can't find a way to ...
0
votes
1answer
68 views

Figuring out the AC equivalent circuit(re model) of a Pre-Amplifier and Tone Control Circuit

I need help figuring out the AC equivalent circuit of this preamplifier circuit. I'm quite familiar with all the simple BJT configurations but this is my first configuring such a relatively ...
0
votes
2answers
118 views

Working of the LM-358 - microphone circuit

I had this task of converting the output of a microphone's voltage (data-sheet link attached) to a range of 0-5V, as this is the range required for the input to an ADC chip. While I know that op amps ...
3
votes
1answer
193 views

NPN Transistor Pre-Amp Circuit - How do I calculate gain and voltage output?

I am calculating the voltage output of the below circuit. The output I have calculated varies by 0.1 of a volt compared with the simulation I created using multisim, but I am not certain this is ...
2
votes
1answer
190 views

Vintage Oscilloscope Preamp Whitepaper

Sometime early 90s I came across a whitepaper published by an oscilloscope manufacturer that described a custom preamp IC they had developed for their scopes. Does anyone know of this article? The ...
1
vote
2answers
133 views

Pre-amplifier biased to one-half of power source

There is a schematic of an pre-amplifier that use one-half of voltage source output biasing (T1 emitter is one-half of V1). How the resistive network was calculated to allow one-half output Q-point? ...
0
votes
1answer
187 views

Is the SSM2019 an appropriate IC for a optical sound solar cell preamplifier?

I am restoring a 35mm film projectors from the 1930s, which at some point had a Kelmar optical sound head added onto it. The solar cell outputs a balanced signal through an XLR jack that is very weak (...
1
vote
2answers
167 views

OP Amp as audio preamp - am I doing it right?

I have a design that uses an ATXMega32E5 for two audio sources. In one case, a timer output square wave (3.3v logic) goes through a low-pass filter to make beeps, and in the other case, a DAC channel ...
2
votes
3answers
3k views

Need some help building a TL072 preamp circuit

I have an early 70's Magnavox turntable/radio console that I want to be able to plug my smartphone into so that I can use it as an external speaker. I'm plugging into the Tape In input, which is an ...
0
votes
2answers
204 views

piezo stereo preamp

I have found several projects on piezo preamps but I cant find anything that can run 2 piezo inputs to make it stereo and uses potentiometer to control volume gain etc. What I found is "Collin’s Lab: ...
0
votes
1answer
108 views

Can I add an audio jack to a digital audio board?

Can I use the preamplified audio signal on an iphone only microphone (Tascam iM2) to add an audio jack? There is already a USB 5V input which perhaps powers the preamp, and a volume control where I ...
3
votes
2answers
458 views

Why is my microphone circuit not working?

I'm trying to make a simple microphone/speaker circuit with a PreAmp and an Op-Amp. Currently, the speaker just outputs a high ...
0
votes
1answer
138 views

Troubleshooting noisy FET buffer for contact mic

I'm trying to follow the schematic on this page to create a preamp/impedance matcher for a balanced piezo contact mic. I've reproduced the schematic below. I've built it on a breadboard and I'm ...
0
votes
1answer
235 views

How to test the input impedance of a Microphone Preamp?

How would someone test the input impedance of a microphone preamp? I have all the necessary equipment i.e. oscilloscope and multi-meters but I'm struggling to find information on the topic.
2
votes
0answers
184 views

Dual antiphase electret mic preamp topology

I am currently trying to make a preamp for an electret mic pair, which are placed physically in antiphase. The main idea is to subtract one mic's signal from another and therefore boost the signal ...
3
votes
1answer
2k views

What is the best preamplifier circuit for electret condenser microphone?

I have one old German directional dynamic microphone "SEL BST 205-1" and I remove everything inside it and pack 2 condenser microphones from mobile phones "Nokia 5130". Like preamp I use this ...
3
votes
2answers
351 views

How can I attach an analog to digital converter to a guitar

I want to modify an electric guitar to add an ADC and microcontroller to drive some LEDs for fancy effects that follow music. Since typical output levels of pickups are about 100mV, I was thinking of ...
0
votes
2answers
272 views

MPC508AP as central IC on audio input selector board

I am working on audio preamp and for the input selector I've created following design: Now, as you can see, I've chosen Texas Instrument's MPC508AP Analog Multiplexer for input switching IC. However, ...
1
vote
5answers
301 views

Op Amp - Specifications are given for unity gain, how to choose another gain?

TL081 datasheet gives the following specifications: How can I find the open loop amplification? I know that the relationship between the differential voltage amplification and the (closed or opened?) ...
0
votes
1answer
154 views

Analog front end electronics

I am currently working on a project that involves designing some front end electronics that shape the charge pulse from a solid state detector (effectively a current source - I1 on the diagram). Our ...
-1
votes
1answer
163 views

Reduce power consumption for AN7316 amplifier

I have a pre-amplifier with AN7316 from a tape recorder. Currently it draws 24mA from a very small 12V battery (I think it is an A23). The IC has two parts: a "play" amplifier and a "rec" amplifier. ...
1
vote
1answer
115 views

HPF cut-off in microphone pre-amplifier

In the below circuit, do Rbias and R2 both affect the cut-off frequency? Or is it simply 1/2*pi*R2*C2
0
votes
2answers
266 views

Some questions regarding input stage of audio signals to the pre-amplifier

I'm very new to audio circuits but for the sake of curiosity I want to simulate an approximate version of a circuit of an audio input along with a smartphone pre-amp stage in LTspice. I will have five ...
6
votes
4answers
3k views

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?
0
votes
1answer
538 views

Preamp for Magic Eye VU meter [closed]

I want to build a Magic Eye Tube VU. This tutorial http://www.antimath.info/electro/vu-meter-em84/ says: If this circuit is used with a tube amplifier, the “IN” connection in the picture is ...
1
vote
1answer
320 views

Converting single-ended line audio to differential, on single supply?

I built an audio amplifier based on TI's TAS5630 IC. This is a Class-D amp with multiple configurations. I'm using it as a 2-channel amp. The problem is that this configuration requires a differential ...
1
vote
2answers
648 views

Soft fade out circuit for turning off speakers

I have some loud speakers connected to an amplifier. The problem is when I turn the preamp off, it sends a loud POP noise through the speakers. The turn off of the amp is delayed by 1 or 2 seconds, ...
5
votes
1answer
748 views

phono preamp hum - ground loop?

I've built a simple 2 stage active/passive phono preamp. Everything in terms of amplification/frequency response/lack of distortion works fine - just as it was designed. The only thing is that hum can ...
4
votes
1answer
347 views

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 ...
0
votes
3answers
449 views

Using Microphone preamplifier IC Max4468

I am designing microphone preamplifier using MAX4468 (datasheet), but the reference diagram shows output from microphone (microphone input) going to both inverting and non-inverting terminals of the ...
1
vote
0answers
438 views

Replacing trim pots with potentiometers?

I have been looking at and considering building the following circuit from Beavis Audio Research. Their explanation of the circuit: Around 1965, Marshall introduced a few amps built around an 18 ...