Introduction to the OPA1642 Op-Amp
The Texas Instruments OPA1642 is a high-performance audio op-amp. It delivers ultra-low noise of just 2.5 nV/√Hz. In addition, it achieves 0.00001% THD+N at 1 kHz. As a result, engineers rely on the OPA1642 across professional audio signal chains worldwide. See our product in LCSC.
Key Takeaways
- The OPA1642 delivers 2.5 nV/√Hz noise, among the lowest in its class.
- It achieves 0.00001% THD+N, making it ideal for studio-grade audio.
- JFET inputs give the OPA1642 very low bias current for clean signal paths.
- The OPA1642 is unity-gain stable and needs no external compensation.
- Engineers can choose SOIC-8 or VSSOP-8 packages depending on production needs.
What Is the OPA1642 Op-Amp?
The OPA1642 is a dual JFET-input operational amplifier from Texas Instruments, optimised for professional audio applications. It was first introduced to replace older JFET op-amps, and it offers significant performance gains. Therefore, engineers use the OPA1642 wherever signal fidelity is critical.
JFET Input Stage Advantages
JFET inputs give the OPA1642 very high input impedance. Input bias current is only 5 pA typical, which is far lower than BJT input op-amps. As a result, the OPA1642 suits high-source-impedance circuits without DC offset issues.
Audio Performance Benchmarks
THD+N of 0.00001% is among the lowest in its class. Meanwhile, the 11 MHz gain bandwidth product supports wide audio bandwidth. For example, high-resolution 192 kHz audio paths benefit from this headroom. In addition, the 20 V/µs slew rate handles fast transient signals cleanly.
Technical Specifications Table
The table below lists key electrical parameters for the operational amplifier. All values reflect typical 25°C conditions unless stated.
| Parameter | Symbol | Value | Unit | Notes |
| Supply Voltage | VS | ±2.25 V to ±18 V | V | Single or dual supply |
| Input Voltage Noise | en | 2.5 | nV/√Hz | At 1 kHz |
| THD+N | — | 0.00001% | % | At 1 kHz, RL = 2 kΩ |
| Gain Bandwidth Product | GBW | 11 | MHz | Unity-gain stable |
| Slew Rate | SR | 20 | V/µs | Typical |
| Input Bias Current | IB | 5 | pA | Typical, at 25°C |
| Quiescent Current | IQ | 3.8 | mA | Per channel |
| CMRR | — | 120 | dB | Typical |
| Output Voltage Swing | — | ±(VS – 1.2V) | V | Typical, RL = 2 kΩ |
| Operating Temperature | TA | –40 to +125 | °C | Full range |
Specifications referenced from the Texas Instruments OPA1642 datasheet.
Key Features for Audio Design
Low-Noise OPA1642 Input for Audio Signal Chains
The 2.5 nV/√Hz voltage noise is exceptionally low for a JFET op-amp. Competing JFET devices often exceed 8 nV/√Hz. Therefore, the OPA1642 reduces the noise floor in sensitive preamp stages, which results in cleaner recordings at every sample rate.
CMRR and Power Supply Rejection
CMRR reaches 120 dB typical, which rejects interference from ground loops and power supplies. In addition, PSRR is 120 dB, protecting the signal from rail noise. Consequently, audio performance remains stable in electrically noisy environments.
Rail-to-Rail Output Swing
Output voltage swings to within 1.2 V of each supply rail. This maximises dynamic range at low supply voltages. For example, a ±5 V supply yields usable output to ±3.8 V. Engineers can therefore use lower supply rails without sacrificing headroom.
Audio Application Scenarios
OPA1642 in DAC Output Stage Filter Design
Digital-to-analogue converters require a low-noise reconstruction filter. The OPA1642 handles this task with minimal added noise. Its low THD also preserves DAC performance at all output levels. For instance, high-end streaming DACs use the OPA1642 in their I/V conversion stage.
Microphone Preamp Circuit
Condenser microphones present high source impedances. The JFET input of the OPA1642 suits this perfectly. Input bias current stays below 5 pA, which prevents DC loading. Therefore, the OPA1642 preserves both gain accuracy and noise performance.
OPA1642 in Active Crossover and Filter Networks
Active audio crossovers require flat frequency response and low phase distortion. The 11 MHz GBW provides ample loop gain at audio frequencies. In addition, unity-gain stability simplifies Sallen-Key and multiple-feedback filter topologies. As a result, engineers can implement high-order crossovers without instability concerns.
OPA1642 as an ADC Input Driver for High-Resolution Audio
High-resolution ADCs demand drivers with very low THD. The OPA1642 meets or exceeds the linearity of most 24-bit converters. Its slew rate of 20 V/µs handles 192 kHz full-scale signals cleanly. Consequently, the OPA1642 remains a preferred driver for studio-grade analogue front ends.
Configuration and Circuit Options
Inverting and Non-Inverting Gain Configurations
The OPA1642 supports both inverting and non-inverting gain stages. Use 1% metal film resistors to minimise gain error. For example, a gain of 10 V/V requires a 10 kΩ feedback resistor and 1 kΩ input resistor. Always bypass supply pins with 100 nF ceramic and 10 µF electrolytic capacitors.
Dual-Supply vs Single-Supply Operation
Dual-supply operation from ±15 V maximises dynamic range. Single-supply operation from 9 V to 36 V works well for portable devices. In addition, a virtual ground midpoint allows AC-coupled single-supply designs. Therefore, choose the supply configuration based on headroom and power budget.
Procurement and Availability
Texas Instruments manufactures the operational amplifier in two package options. The SOIC-8 suits hand-soldering and prototyping work. Meanwhile, the VSSOP-8 is preferred for compact SMT production runs. Both packages are RoHS-compliant and AEC-Q100 screened for automotive grades.
OPA1642 Package and Lead Time Considerations
Standard SOIC-8 typically ships within two weeks from authorised distributors. VSSOP-8 may require longer lead times during supply constraints. For example, ordering the OPA1642 via LCSC or Mouser often yields faster fulfilment. Tape-and-reel formats also support automated SMT assembly at scale.
OPA1642 vs Competing Audio Operational Amplifier
The table below compares against other popular audio op-amps. Use this comparison to select the right device for your design.
| Device | Input | Noise (nV/√Hz) | GBW (MHz) | THD+N | Best For |
| OPA1642 | JFET | 2.5 nV/√Hz | 11 MHz | 0.00001% | Best audio, low THD |
| OPA2134 | JFET | 8 nV/√Hz | 8 MHz | 0.00008% | General audio use |
| NE5532 | BJT | 5 nV/√Hz | 10 MHz | 0.002% | Budget audio designs |
| LME49720 | BJT | 2.7 nV/√Hz | 55 MHz | 0.00003% | High-speed audio |
The OPA1642 leads on THD+N and has the lowest noise among JFET options. BJT-based devices like the LME49720, however, offer higher GBW for demanding applications. Therefore, choose the OPA1642 where audio fidelity is the primary requirement.
Frequently Asked Questions
What Is the OPA1642 Operational Amplifier Used For?
The OPA1642 is used in audio circuits that require ultra-low noise and THD. Engineers select it for DAC output stages, ADC drivers, and studio recording equipment. Its JFET input also makes it well suited to high-impedance microphone preamps. Many designers favor it specifically because its noise floor stays low even at higher gains, which preserves dynamic range in sensitive front-end stages.
Can the OPA1642 Run on a Single Supply?
Yes, it operates from 9 V to 36 V on a single supply. This range makes it suitable for portable and battery-powered audio devices. A virtual ground midpoint also allows AC-coupled single-supply designs when a dual rail is not available. Engineers should bypass supply pins with both ceramic and electrolytic capacitors regardless of supply configuration to maintain stable performance.
How Does the OPA1642 Compare to the OPA2134?
The OPA1642 has lower THD and lower voltage noise than the OPA2134. Both devices share a JFET input stage and unity-gain stability, but the OPA1642 pulls ahead in noise floor and distortion figures. As a result, the OPA1642 is the better choice for professional-grade audio signal chains, while the OPA2134 remains a solid option for general-purpose audio designs with a smaller budget.
Is the OPA1642 Unity-Gain Stable?
Yes, it is stable in unity-gain configurations without external compensation. This simplifies design for most audio applications, including buffer stages and simple gain blocks. Because no extra compensation network is needed, engineers can reduce component count and board space in space-constrained audio designs.
What Package Options Are Available for the OPA1642?
The OPA1642 comes in SOIC-8 and VSSOP-8 packages. Both options suit compact PCB layouts in space-constrained audio equipment. SOIC-8 is easier to hand-solder during prototyping, while VSSOP-8 saves board space in high-volume SMT production. Engineers should select the package based on assembly method and available board real estate.
Conclusion: OPA1642 for Professional Audio
The Texas Instruments operational amplifier is a top-tier choice for audio circuit design. Its 2.5 nV/√Hz noise and 0.00001% THD+N are class-leading specifications. First, confirm your supply voltage and gain requirements. Next, select SOIC-8 for prototyping or VSSOP-8 for production. Finally, follow TI’s recommended bypass and layout practices. As a result, the OPA1642 delivers professional-grade audio performance in your design.
Find What You Need on LCSC
Finding the right operational amplifier for your audio design is easy on LCSC. LCSC stocks the OPA1642 in both SOIC-8 and VSSOP-8 packages, alongside comparable devices like the OPA2134 and NE5532. You can filter by package type, compare pricing, and order in prototype or production quantities. Start browsing the OPA1642 listing today.
