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.

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55 views

Sound through the earphone is also sent to the amplifier when using a jack splitter after a audio mixer

I implemented the following audio mixer circuit with just 2 input audio sources: http://www.theorycircuit.com/audio-mixer-circuit/ Both sounds got mixed properly. Then, at the end of that audio ...
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66 views

Ultra low noise power supply for pre-amp

I have designed the following power supply smoothing circuit for my turn table preamp. This will be powered by a 24V 'wall-wart' type adapter. I tried to combine a transistor/zenner diode voltage ...
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43 views

How to make a preamp that is ON when input is a MIC but OFF when a LINE level?

My question is very simple: Is there a way to create a "preamp" circuit that is automatically ON when there is a MIC connected (for example, a desktop PC microphone) but OFF when there is a LINE ...
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72 views

TL082 electret preamp and LM386 power amp

I have spent the last few days trying to prototype a TL082 electret mic preamp (based on this schematic). I swapped the TL071 in ...
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67 views

Need to identify this 3-pin Connector to a small amp. It's a Pre-Amp input

I could use the neighbouring 3.5mm stereo jack for sound input, but those connections are flimsy. It's a 3-pin connector, 10mm long, 6mm wide and 7mm high with alignment slots on all sides but the ...
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40 views

Safely connecting a preamp powered by a benchtop DC power supply to a power amp

I pulled the preamp out of a broken guitar combo amp. The preamp has positive, negative, and ground leads for powering it at +/-25V. I would like to power the preamp with a dual channel benchtop power ...
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54 views

Alternative ways to step up voltage?

I want to drive an EOM crystal at 20 MHz for phase modulation. I recently bought a step up RF transformer (1:4 turns ratio), but it's not working fine above 2 MHz. I tried winding a transformer myself ...
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58 views

Choosing an OpAmp for MEMS mic preamp stage

I am trying to create an updated version of a mems mic board, like this one from sparkfun. They use an INMP401 mems mic (which is not recommended for new designs) and an OPA344 for the preamp stage (...
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Circuit to power a preamp for a dynamic mic powered by the mixer's phantom power

I really hope that someone will be able to help me out with this. I have looked just about everywhere and left this question up at three chat rooms. I want to build a preamp circuit for a low output ...
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123 views

12AX7 Valve Overdrive/Distortion Effect Pedal

I'm following the schematic below using the recommendations plus a couple of extra LEDs. With the footswitch in the enabled position, I'm not getting any sound. In the bypass position, the input and ...
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66 views

Help identifying a photodiode pre-amp PCB

Recently I found this PCB in a electronics junk bin. It's said that it's a photodiode preamp, but I was not able to find the datasheet or any information about the board. Since the PCB looks neatly ...
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62 views

Impedance match Fishman guitar pre-amp to IRIG2HD

I'm looking for some help in understanding impedance matching. I'm hoping one or more of you technically savvy electronics folks will jump in and give me a simple circuit recommendation. ...
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55 views

Designing Mic with integrated preamplifier

I would like to design from scratch a battery powered large diaphragm mic with integrated opamp preamplifier to 3.5mm line out jack for pc. I have two capsules. One from a t.bone sc400 and one RK-47....
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41 views

Car microphone; very low signal

I would like to use a car microphone for bluetooth communication. The mic is a BMW one: 84316938762. The wiring diagram (TIS) marks the mic's two connectors for the pin 1 and 2: TIS (X18507). ...
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40 views

Need help with choosing the right pre-amplifier for my rural base station design

I am in the process of designing a multi radio base station for a FWA application. The distance from the main base station to the terminating units is a 1 KM. I have 2 sectors and am planning to use ...
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93 views

Op-Amp output voltage exceeds the power rail voltage (in simulation)

I'm designing a RIAA pre-amplifier based on the 2 op-amps from an NE5532 package. It seems that something is wrong, because the output of the 2nd stage is giving a 400V output which is way above the ...
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136 views

Simple 12V preamp circuit before speaker

In my apartment building, we have an intercom system with one central unit and multiple terminals, one per apartment. Unfortunately, after some unknown tweaks done a couple of years ago to the central ...
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56 views

Guitar to iPhone JFET pre-amp circuit issue

I am following this tutorial to build a simple JFET pre-amp to connect a guitar to an iphone. This is the schematic: I have soldered the components as per the schematic directly onto the 1/4" mono ...
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110 views

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 ...
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1answer
100 views

Op amp circuit with two capacitors

Based on an electronics lecture, we are dealing now with the preamplifier circuit for a detector. The figure is shown below. Actual I am having the problem to understand the center operational ...
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115 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 ...
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164 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 ...
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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 ...
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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, ...
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1answer
273 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 ...
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2answers
122 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 ...
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1answer
421 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...
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71 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 ...
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358 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 ...
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154 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 ...
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1answer
265 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 ...
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1answer
253 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 ...
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144 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 ...
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1answer
203 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 ...
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204 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-...
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408 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 ...
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328 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 ...
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504 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 ...
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1answer
66 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 ...
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1answer
112 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 ...
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2answers
148 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 ...
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1answer
292 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 ...
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228 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 ...
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151 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? ...
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1answer
315 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 (...
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222 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 ...
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5k 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 ...
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2answers
285 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: ...
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1answer
120 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 ...
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2answers
610 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 ...