Microphone Amplifier
If you have been hunting for the sensitive sound pick-up circuit, then you have found it right. The schematic presented on this website can be adapted to function as a variety of differen…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
Microphone Amplifier is a electronics project. If you have been hunting for the sensitive sound pick-up circuit, then you have found it right. The schematic presented on this website can be adapted to function as a variety of differen…
- Source pages
- 338-340
- Named parts
- 10
- Build goal
- Working, tested prototype
Tools you need
- Digital multimeter
- Wire stripper and side cutters
- Soldering iron with a fine tip
- Current-limited bench supply
Use eye protection, good lighting, and a clean insulated surface throughout the build.
Safety precautions
- Disconnect every power source before changing a connection.
- Check component polarity, pinout, and supply voltage twice.
- Use a current limit for the first power-up.
- Keep liquids, loose metal, and uninsulated wires away from the bench.
Gather, identify, and understand every part.
Use the standardized inventory, then open What's this? to learn each part's role, advantages, limitations, handling, and specifications.
What's this?Image, role, pros, cons, handling & specifications
Resisters
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for Resisters; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
What's this?Image, role, pros, cons, handling & specifications
VR=11 KΩ
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for VR=11 KΩ; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
What's this?Image, role, pros, cons, handling & specifications
C1=47μ , 10V; C2,C3=0.1μ; C4=220μ, 10V; C5=10μ
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for C1=47μ , 10V; C2,C3=0.1μ; C4=220μ, 10V; C5=10μ; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
What's this?Image, role, pros, cons, handling & specifications
Miscellaneous
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for Miscellaneous; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
What's this?Image, role, pros, cons, handling & specifications
Battery of the 6 Volt Type BATT
A power component supplies, converts, stores, or regulates energy for the project.
What it does hereIt must provide the documented voltage, polarity, isolation, and sufficient current safely.
Buy / compare this part ↗Advantages
- Stable power improves reliability
- Current limiting protects first tests
- Regulation reduces resets and noise
Limitations
- Wrong polarity can cause immediate damage
- Underrated parts overheat
- Mains circuits require qualified supervision
Handling
- Measure output before connection
- Use a fuse or current limit
- Insulate exposed conductors
Specifications to verify
- Use the exact model, value, package, and rating listed for Battery of the 6 Volt Type BATT; similar-looking parts are not always interchangeable.
- Confirm input/output voltage, current, polarity, connector, isolation, and thermal rating.
What's this?Image, role, pros, cons, handling & specifications
Microphone with a Condenser (MIC)
A sensor converts a physical condition into an electrical signal the circuit can measure.
What it does hereIt provides project input as an analogue, digital, resistive, frequency, or calibrated signal.
Buy / compare this part ↗Advantages
- Adds real-world awareness
- Can usually be tested independently
- Often supports calibration
Limitations
- Readings can drift
- Placement affects results
- Some sensors need warm-up or calibration
Handling
- Protect the sensing surface
- Observe supply voltage and polarity
- Keep signal leads away from noisy power wiring
Specifications to verify
- Use the exact model, value, package, and rating listed for Microphone with a Condenser (MIC); similar-looking parts are not always interchangeable.
- Confirm supply range, output type, measurement range, accuracy, response time, and pin order.
What's this?Image, role, pros, cons, handling & specifications
OTHER
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for OTHER; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
What's this?Image, role, pros, cons, handling & specifications
BC149C - transistor
A semiconductor stage performs switching, amplification, regulation, rectification, or logic.
What it does hereIt controls current or signal flow at a defined point in the circuit.
Buy / compare this part ↗Advantages
- Fast and efficient
- Compact
- Can control larger loads from smaller signals
Limitations
- Pin order varies
- Sensitive to overvoltage and reverse polarity
- May need cooling or bias components
Handling
- Verify the datasheet pinout
- Avoid static and soldering heat
- Check notch, stripe, or flat-face orientation
Specifications to verify
- Use the exact model, value, package, and rating listed for BC149C - transistor; similar-looking parts are not always interchangeable.
- Confirm pinout, maximum voltage/current, dissipation, gain or forward voltage, and package.
What's this?Image, role, pros, cons, handling & specifications
BC147B - transistor
A semiconductor stage performs switching, amplification, regulation, rectification, or logic.
What it does hereIt controls current or signal flow at a defined point in the circuit.
Buy / compare this part ↗Advantages
- Fast and efficient
- Compact
- Can control larger loads from smaller signals
Limitations
- Pin order varies
- Sensitive to overvoltage and reverse polarity
- May need cooling or bias components
Handling
- Verify the datasheet pinout
- Avoid static and soldering heat
- Check notch, stripe, or flat-face orientation
Specifications to verify
- Use the exact model, value, package, and rating listed for BC147B - transistor; similar-looking parts are not always interchangeable.
- Confirm pinout, maximum voltage/current, dissipation, gain or forward voltage, and package.
What's this?Image, role, pros, cons, handling & specifications
T1, T2 - transistor stages identified in the circuit
A semiconductor stage performs switching, amplification, regulation, rectification, or logic.
What it does hereIt controls current or signal flow at a defined point in the circuit.
Buy / compare this part ↗Advantages
- Fast and efficient
- Compact
- Can control larger loads from smaller signals
Limitations
- Pin order varies
- Sensitive to overvoltage and reverse polarity
- May need cooling or bias components
Handling
- Verify the datasheet pinout
- Avoid static and soldering heat
- Check notch, stripe, or flat-face orientation
Specifications to verify
- Use the exact model, value, package, and rating listed for T1, T2 - transistor stages identified in the circuit; similar-looking parts are not always interchangeable.
- Confirm pinout, maximum voltage/current, dissipation, gain or forward voltage, and package.
Connect one verified path at a time.
Explore the named components and standardized signal flow, then use Source Check to verify exact physical pins, values, and topology before applying power.
Trace this circuit.
Microphone Amplifier: interactive parts, standardized terminals, responsive anchored wires, student explanations, and the original circuit reference in one shared system.
Trace before wiring
Follow power, ground, inputs, processing, and outputs in that order. Never guess a pin from package shape alone.
Connect with power off
Make short, labelled connections and share a common ground only where the schematic requires it.
Inspect every joint
Check continuity, polarity, adjacent shorts, and loose connections before the first power-up.
Open all source diagrams and build views 1 visuals
Confirm the hardware-only control path.
This project does not include firmware in the source. The circuit itself provides the required behaviour.
How to connect
- Match every controller label to the circuit view and source pin map.
- Join grounds before signal wires when separate low-voltage supplies are used.
- Keep motors, relays, pumps, and other loads on a suitable driver and external supply.
Common mistakes
Reversed VCC/GND, board-label versus GPIO-number confusion, missing common ground, and charge-only USB cables.
Troubleshoot
Disconnect loads, continuity-test one path at a time, then test with a current limit.
Software preparation
No IDE, board package, library, or firmware upload is required for this project.
If you add a programmable controller as an extension, document its pin map separately.
How to upload code
The original design is implemented entirely in hardware, so proceed after verifying the circuit and supply.
Assemble, deploy, test, and troubleshoot.
Use the complete source notes in build order, then pass the final checks before calling the project finished.
Build in functional stages
- Power and regulation
- Controller or processing stage
- Inputs and sensors
- Outputs and loads
- Enclosure and strain relief
Power up safely
- Inspect unpowered continuity first
- Apply the lowest safe current limit
- Measure supply rails before signals
- Add one load at a time
- Record expected and actual results
Work from simple to complex
- Confirm power, ground, polarity, and orientation
- Compare each pin with the source
- Test inputs separately from outputs
- Replace only one variable at a time
- Power off before every correction
Follow the documented instructions.
These notes come from this project's source and remain in their original order.
Project overview
Project build noteIf you have been hunting for the sensitive sound pick-up circuit, then you have found it right. The schematic presented on this website can be adapted to function as a variety of different devices. It is possible to combine it with a more complex device as a sound-activated alarm, in addition to using it as a straightforward microphone. This circuit works just as well for a bugging device as it does for other purposes.
Circuit Diagram
Project build noteYou can see that the transducer in this particular circuit is a microphone by looking at the circuit diagram. Due to the relatively low output of the condenser microphone, a FET amplifier is required in order to boost the signal. The R1,R2 resistor network supplies the necessary power for this amplifier circuit. A two-stage amplifier receives the signal from the output of a condenser microphone. The current series feedback is utilized in the first stage by the transistor T1 (BC149C). In the voltage shunt feedback design, the second stage, which is comprised of the transistor T2, is linked. The amplification provided by these two stages is adequate to enable the user to detect even the faintest whisper. The amplifier design on the site calls for a supply of 4.2 volts, which may be achieved by connecting a resistor R9 [1k] in series with the circuit. It is possible to change the value of this resistor so that it is appropriate for a supply voltage that is not 6 volts. When a 10k potentiometer is connected to the circuit in the manner depicted in the diagram, the output of the microphone amplifier can be made variable. Depending on the input sensitivity of the primary amplifier system, increasing the gain of the circuit can be accomplished by lowering the value of resistor R6 to either 47 or 22 ohms. Additionally, an increase in gain was seen when the supply voltage was changed to 3V and R9 was removed entirely. A little enclosure in the shape of a circle should be employed to contain the microphone.
PART LIST
Project build noteResisters R1=1.2 KΩ; R2=2.7 KΩ; R3=33 KΩ; R4=6.8 KΩ; R5=3.3 KΩ; R6=100; R7=560 KΩ; R8=4.7 KΩ; R9=10 KΩ; VR=11 KΩ T1 is equal to BC149C, and T2 is equal to BC147B Capacitors C1=47μ , 10V; C2,C3=0.1μ; C4=220μ, 10V; C5=10μ Miscellaneous Battery of the 6 Volt Type BATT Microphone with a Condenser (MIC) OTHER PCBs, connecting wires, hardware, and so on are all included.
You built Microphone Amplifier.
You followed the full workflow from understanding the mission to testing the finished project. That is a real engineering achievement - well done.
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