Headphone amplifier based on OPA2188

1. Product Introduction

This product is an audio amplifier used to drive high-impedance headphones. It adopts a large-loop feedback architecture to ensure high audio fidelity. The output stage works in Class A and B states, which balances output fidelity and static power consumption as much as possible.

2. Application scenarios

High-fidelity audio power amplification for headphones.

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

3. Product overview

The large loop feedback architecture is adopted to ensure the highest audio fidelity as much as 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 the operational amplifier with EMI HARDENED characteristics is selected to avoid the radio frequency signal of the mobile phone from interfering with the amplifier.

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

The panel is made of aluminum substrate, the Gerber file has been uploaded as an attachment, and you can make samples at the aluminum substrate proofing factory by yourself. 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, first weld the positive and negative power supply parts. After confirming that the voltage is about 6.5V, the subsequent amplifier circuit can be welded.

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

4. Product parameters

Output internal resistance: 10 ohms

Output voltage range: about +-5.5V (peak value)

Default Gain: 2

Input signal range: +-1Vrms

Frequency response range: 20-20000Hz

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

Interface: both input and output are 3.5mm headphone jack, 3-wire, stereo

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

Figure 1 of the hardware project of headphone amplifier based on OPA2188

5. Instructions for use

Please weld the battery wires according to the sequence of positive and negative poles marked on the battery wires.

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

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

6. Remarks

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 pasted, but the ability to resist electromagnetic interference will decrease.

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

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

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

The attached compressed file is the Gerber file of the front and rear panels, which can be used as an aluminum substrate for proofing.