The Texas Instruments OPA1622 is one of the highest-performance devices in the SoundPlus™ audio operational-amplifier family.
It combines very low noise, extremely low distortion, high open-loop gain, excellent common-mode rejection, and unusually strong output-current capability in one compact dual operational amplifier.
Although it was originally designed for premium headphone amplifiers, the OPA1622 is also highly suitable for use as a:
Many audio operational amplifiers can provide low noise and low distortion when driving an easy load. The OPA1622 is different because it was designed to maintain excellent linearity while supplying much greater output current.
Texas Instruments specifies a typical short-circuit output-current capability of approximately +145 mA / −130 mA. This makes the OPA1622 much more capable of driving demanding loads than a normal low-current audio opamp.
It also offers very low input-voltage-noise density of 2.8 nV/√Hz at 1 kHz, common-mode rejection of up to 127 dB, and open-loop gain of up to 136 dB under the specified test conditions.
These characteristics make it especially useful when a circuit requires both high resolution and strong control of the following stage.
The OPA1622 has received very different reviews in the DIY audio community. Some listeners consider it ordinary, while others describe it as one of the finest operational amplifiers they have used in a preamplifier, DAC output stage, or buffer.
In our experience, the difference often comes from implementation.
A high-speed, high-current amplifier depends heavily on PCB layout, local power-supply impedance, grounding, decoupling, and the load connected to its output.
When it is installed on a simple adapter board without proper local decoupling or output isolation, its performance may become inconsistent. In a poor layout, the listener may never hear what the OPA1622 can actually provide.
We did not simply mount the OPA1622 on a small conversion board. The module was designed specifically to provide a short, stable, and low-impedance operating environment around the amplifier.
Six Murata multilayer ceramic capacitors are installed directly around the OPA1622 power-supply path.
Three different capacitor values are used so their electrical characteristics can complement one another over a wider frequency range. The shortest practical current path helps reduce local supply impedance and provides the amplifier with a more stable power source.
Carefully selected resistors are installed in the output paths to improve isolation from capacitive loads and reduce the possibility of unwanted high-frequency oscillation.
The amplifier, local capacitors, and output-stability components are placed close together to keep critical high-frequency current paths short.
The purpose of this design is not to change the character of the OPA1622. It is to allow the amplifier to operate in a more stable and carefully controlled environment.
At VALAB, we evaluated the OPA1622 primarily as an audio buffer rather than only as a headphone driver.
Among the many operational amplifiers we have used, the OPA1622 belongs in the top level. In a properly implemented buffer stage, it provides a highly transparent presentation with strong detail retrieval, precise imaging, clean dynamics, and excellent control.
We have successfully used this module in place of the LT1028 in a buffer-stage application. The OPA1622 performed extremely well while also providing much greater output-current capability.
Sound quality always depends on the complete circuit, power supply, grounding method, load, and system matching. No operational amplifier can correct every weakness in the surrounding equipment.
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DAC Output Buffer High linearity, low noise, and strong output drive for connection to cables and following stages. |
Line Driver Suitable for driving lower-impedance loads and longer interconnect cables with good control. |
Preamplifier Buffer Useful where high input quality and low output impedance are required. |
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Headphone Driver Designed by TI for high-fidelity headphone-driving applications. |
Active Output Stage Appropriate where a conventional low-current audio opamp does not provide sufficient drive. |
Professional Audio Suitable for audio equipment that requires low noise, high channel separation, and stable line-level output. |
| Specification | Typical Performance |
|---|---|
| Device | Texas Instruments OPA1622 SoundPlus™ |
| Configuration | Dual bipolar-input audio operational amplifier |
| Input-Voltage-Noise Density | 2.8 nV/√Hz at 1 kHz |
| THD+N | As low as −132 dB under specified test conditions |
| Short-Circuit Output Current | Approximately +145 mA / −130 mA typical |
| Open-Loop Gain | Up to 136 dB typical |
| Common-Mode Rejection Ratio | Up to 127 dB typical |
| Channel Separation | 140 dB typical at 1 kHz |
| Slew Rate | 10 V/µs typical |
| Dual-Supply Range | ±2 V to ±18 V |
Electrical values are based on the Texas Instruments OPA1622 datasheet. Actual performance depends on operating voltage, load, circuit configuration, temperature, and measurement conditions.
Excellent specifications are only the beginning.
Our goal is to provide outstanding audio devices with the operating environment they need: stable local power, short signal paths, careful component selection, and practical control of high-frequency behavior.
In many audio circuits, correct implementation makes a greater difference than simply changing from one famous operational amplifier to another.