In this DIY electronics project, we’ll guide you through the process of building a precision audio preamplifier using the INA117KU, a low-noise instrumentation amplifier. Audio preamps are critical for boosting low-level audio signals, such as those from microphones or electric guitars, to a level that can be further processed by other audio equipment. The INA117KU is an excellent choice for this project due to its low distortion, high precision, and adjustable gain.
This project does not require any coding, formulas, or complicated forms—just a basic understanding of audio electronics and hands-on assembly. The preamp built here can be used for a variety of audio applications, from professional audio equipment to home recording studios.
The INA117KU is a precision instrumentation amplifier that provides high input impedance, low noise, and precise gain control. It is ideal for applications that require amplifying small signals while maintaining a high degree of accuracy and clarity. This IC is commonly used in audio applications, sensor interfacing, and other low-level signal processing tasks. The INA117KU uses a single-supply or dual-supply voltage and can be adjusted for various gain settings with external resistors.
What makes this chip particularly useful for audio preamplification is its ability to amplify weak signals, such as those from microphones or other audio sources, without introducing unwanted distortion or noise. It also allows for fine-tuned gain adjustments, making it a versatile option for achieving clean and precise amplification.
For this project, you will need the following components:
1. INA117KU Instrumentation Amplifier IC
2. Resistors – Various values for setting gain and filtering (e.g., 10kΩ, 100Ω)
3. Capacitors – For noise filtering and signal smoothing (e.g., 100nF, 10µF)
4. Potentiometer (10kΩ) – For adjusting gain manually
5. Transistor (e.g., 2N2222) – For output buffering
6. Power Supply (±12V or 9V battery) – To power the circuit
7. Audio Input (Microphone or Electric Guitar) – For testing the preamp
8. Audio Output (Speakers or Headphones) – For monitoring the output signal
9. PCB or Breadboard – For assembling the components
10. Audio Jack (1/4-inch or 3.5mm) – For input and output connections
11. Soldering Iron and Solder – To assemble the components
12. Wires – For making connections
Before we begin building the circuit, let’s break down the basic components and their functions.
● INA117KU: The INA117KU will be the heart of the preamp. This chip amplifies the audio signal, preserving fidelity and minimizing noise. The gain of the INA117KU can be adjusted by connecting an external resistor between the pins, and the gain will directly influence how much the signal is amplified.
● Potentiometer: A 10kΩ potentiometer will be used to adjust the gain of the preamp. By rotating the potentiometer, you can smoothly control the amplification level. The potentiometer will be placed between the gain-setting resistor pins of the INA117KU.
● Transistor Buffer: A small NPN transistor (e.g., 2N2222) can be added to buffer the output, ensuring that the signal is strong enough to drive a load (such as headphones or a speaker) without distortion. This buffer also helps with impedance matching between the preamp and the output device.
● Power Supply: The INA117KU requires a dual power supply, typically ±12V, but you can also use a 9V battery depending on your design needs. The dual supply allows the signal to swing both positive and negative, which is essential for audio signals.
Start by placing the INA117KU IC on your breadboard or PCB. The INA117KU comes in a 8-pin dual in-line package (DIP), so be sure to insert it in a way that each pin is connected to its respective rail.
1. Connect the V+ pin (pin 7) to the positive voltage rail (+12V or +9V).
2. Connect the V- pin (pin 4) to the negative voltage rail (-12V or ground, depending on your power setup).
3. Connect the Ref pin (pin 5) to ground. This will set the reference voltage for the signal input.
The gain of the INA117KU can be adjusted by inserting a resistor between pins 1 and 8, the RG pins. A potentiometer connected here allows you to adjust the resistance and thus change the gain. A typical starting point for gain might be 100, but you can experiment with different resistor values to achieve the desired amplification level.
● Place the 10kΩ potentiometer between the RG pins (pins 1 and 8).
● If you prefer a fixed gain, replace the potentiometer with a resistor of the desired value.
To ensure the circuit operates smoothly and does not introduce noise or unwanted frequency components, it’s essential to add capacitors for noise filtering and stabilization.
● Connect a 100nF capacitor between the V+ pin (pin 7) and ground. This helps filter high-frequency noise from the power supply.
● Optionally, add a 10µF capacitor in parallel with the input signal to filter out low-frequency hum.
The input to the preamp can come from various sources such as microphones or electric guitars. For this demonstration, let’s assume you're using a microphone.
● Connect the microphone input to the +IN pin (pin 2). If you’re using a dynamic microphone, it may need additional circuitry like a biasing resistor. If using an electric guitar, the signal is typically already at a suitable level.
● Connect the -IN pin (pin 3) to ground.
To ensure that the output signal is strong enough to drive speakers or headphones, add a simple transistor buffer stage.
1. Use an NPN transistor (e.g., 2N2222).
2. Connect the collector to the output signal, which will be fed to the speakers or headphones.
3. Connect the emitter to ground.
4. Add a 10kΩ resistor from the base of the transistor to the output of the INA117KU to provide the proper biasing.
● Connect the output signal from the transistor’s collector to the audio output jack (1/4-inch or 3.5mm, depending on your equipment).
● The output can now be used to drive headphones, an amplifier, or a recording device.
Once everything is connected, it’s time to test the preamp.
1. Power Up the Circuit: Connect the power supply to the circuit and make sure everything is wired correctly. Ensure the power is within the specified range (+12V and -12V or 9V battery).
2. Adjust the Gain: Use the potentiometer to adjust the gain of the circuit. As you increase the gain, the volume of the output signal should increase.
3. Input Signal: Feed an audio signal into the input (e.g., a microphone or electric guitar). Listen to the output through headphones or speakers. The audio should be amplified without noticeable distortion or noise.
4. Fine-Tuning: If you notice any hum or hiss, check the capacitors and make sure the gain is not set too high. The INA117KU is highly sensitive, so keeping the gain within a reasonable range will help maintain a clean output.
Once you’re satisfied with the performance of the circuit, you can transfer it to a more permanent PCB. Enclose the preamp in a sturdy project box to protect the components and prevent damage from external factors.
● Install the potentiometer and audio jacks on the panel for easy access.
● If you plan to use the preamp in a mobile setup, you can add a battery compartment and an on/off switch.
This DIY audio preamp project using the INA117KU provides a simple, low-noise solution for amplifying weak audio signals, such as those from microphones or electric guitars. By leveraging the high precision and low distortion of the INA117KU, this preamp maintains the integrity of your audio signal, making it suitable for professional audio applications or home recording studios.
With the addition of a potentiometer for gain control and a transistor buffer for output driving capability, the circuit provides a versatile and adjustable preamp solution. Whether you're building it for personal use or as part of a larger audio project, this preamp offers a solid foundation for understanding and working with analog audio amplification.
