Headphone amplifier based on OPA2188

Introduction: A high-fidelity audio power amplifier using OPA2188 operational amplifier as large-loop feedback and 2SC4672 as Class A and B output stages, suitable for use with high-impedance headphones.

1. Product Introduction

This product is an audio amplifier used to drive high-impedance headphones. It uses a large-loop feedback architecture to ensure higher audio fidelity. The output stage works in Class A and B status, balancing output fidelity and Static power.


2. The application scenario

is suitable for high-fidelity audio power amplification of headphones.

The default gain of 2 can be changed by adjusting the feedback network. Therefore, it can also be used to amplify small audio signals.


3. Product overview

uses a large loop feedback architecture to ensure the highest audio fidelity possible. Theoretically THD can be as low as 0.009%.

The input and output interfaces are equipped with magnetic beads to filter the ground, and EMI HARDENED operational amplifiers are selected to prevent the radio frequency signals of mobile phones from interfering with the amplifier.

Although DC-DC is used to provide dual power supplies, a higher operating frequency is set to reduce interference introduced by the power supply as much as possible.

The panel is made of aluminum substrate. The Gerber file has been attached and you can proof it yourself at the aluminum substrate proofing factory. It can also be used as a single-layer PCB proofing, but the shielding performance will be lost.

The circuit has basically been adjusted and finalized. When welding, weld the positive and negative power supply parts first, and only after confirming that the voltage is about 6.5V can weld the subsequent amplification circuit.

Equipped with a DC protection circuit, when the output DC component exceeds 0.5V, the output will be automatically cut off to protect subsequent equipment.


4. Product parameters

Output internal resistance: 10 ohms

Output voltage range: About +-5.5V (peak)

Default gain: 2

Input signal range: +-1Vrms

Frequency response range: 20-20000Hz

Reference theoretical output power: 125mW@32 ohms 32mW @120 ohm

interface: Both input and output are 3.5mm headphone jack, 3 wires, stereo

volume: 20*50*83 (excluding the protruding part of the potentiometer knob)



5. For instructions,

please follow the order of positive and negative poles marked on the battery welding wire. Solder the battery wires.

Connect the input audio signal to the IN port (3.5mm interface on the left), and connect the headphones to the OUT port (3.5mm interface on the right).

Turn the knob clockwise to turn it on, clockwise to increase the volume, and counterclockwise to decrease the volume.


6. Note:

This module is pure hardware and can be used after welding. FB1 and FB2 are magnetic beads. If there are no magnetic beads, 0R can be attached, but the ability to resist electromagnetic interference will be reduced.

The production cost is about 60 yuan, but due to the price increase of OPA2188 and TPS63700, the price may be higher.

The reference size of the aluminum shell is 20*50*80, and TB Chengce shell/universal shell is available.

The reference size of lithium battery is 103040, wire welding type.

The attached compressed files are Gerber files for the front and rear panels, which can be used as aluminum substrate prototypes.


7. Test video

test content: Use a laptop to play music, connect Philips SHP9500 through an amplifier and use a mobile phone to perform two-channel recording to show the amplification effect.