JFET Class A Differential CFB TDA7293 Amplifier
The design process, which began with Revision 1.0, has now been finalized with Revision 2.0.
This hybrid amplifier is the perfect choice for those who, like me, are not fond of chip amplifiers yet find fully discrete designs too complex and achieving high SNR too challenging. It delivers **audiophile-grade** performance while maintaining simplicity.
At the heart of the amplifier is a Class A JFET input buffer, which can be built using JFE2140, LSK389, LSK489, 2SK170, LSK170, or similar devices. Increasing the input bias enhances the **"tube-like" sonic character**, as it has been observed that higher bias levels result in a more pronounced second harmonic presence.
To ensure ultra-low noise performance, the power supply section employs precision low-noise regulators, minimizing unwanted interference. Additionally, a DC servo effectively corrects any offset, bringing it close to 0V.
The amplifier is designed using through-hole (THT) components, making it accessible to those who may find SMD soldering challenging. For those unable to solder precision regulators, 78xx and 79xx footprint-compatible low-noise regulators can be used as an alternative or i can help for original regulators…
**Specifications:**
- **SNR: 103dB @ 1W (crucial for exceptional listening quality)
- **THD: 0.00106%
- **Bandwidth: 5Hz – 75kHz
- **Slew Rate: 9V/µs
- **DC Offset: 200µV (typical)
- **Output Noise:17µV (*input shorted*)
Our inspiration for our design was Bob Cordell's LSK489 application notes and JFE2145 datasheet.
https://www.cordellaudio.com/JFETs/LSK489appnote.pdf
https://www.ti.com/lit/ds/symlink/jfe2140.pdf?ts=1717672324923&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FJFE2140
https://www.st.com/resource/en/datasheet/tda7293.pdf
https://www.ti.com/lit/ds/symlink/tps7a49.pdf?ts=1717660447218&ref_url=https%3A%2F%2Fwww.google.com%2F
https://www.ti.com/lit/ds/symlink/tps7a3001-ep.pdf?ts=1717738722969&ref_url=https%3A%2F%2Fwww.google.com%2F
The design process, which began with Revision 1.0, has now been finalized with Revision 2.0.
This hybrid amplifier is the perfect choice for those who, like me, are not fond of chip amplifiers yet find fully discrete designs too complex and achieving high SNR too challenging. It delivers **audiophile-grade** performance while maintaining simplicity.
At the heart of the amplifier is a Class A JFET input buffer, which can be built using JFE2140, LSK389, LSK489, 2SK170, LSK170, or similar devices. Increasing the input bias enhances the **"tube-like" sonic character**, as it has been observed that higher bias levels result in a more pronounced second harmonic presence.
To ensure ultra-low noise performance, the power supply section employs precision low-noise regulators, minimizing unwanted interference. Additionally, a DC servo effectively corrects any offset, bringing it close to 0V.
The amplifier is designed using through-hole (THT) components, making it accessible to those who may find SMD soldering challenging. For those unable to solder precision regulators, 78xx and 79xx footprint-compatible low-noise regulators can be used as an alternative or i can help for original regulators…
**Specifications:**
- **SNR: 103dB @ 1W (crucial for exceptional listening quality)
- **THD: 0.00106%
- **Bandwidth: 5Hz – 75kHz
- **Slew Rate: 9V/µs
- **DC Offset: 200µV (typical)
- **Output Noise:17µV (*input shorted*)
Our inspiration for our design was Bob Cordell's LSK489 application notes and JFE2145 datasheet.
https://www.cordellaudio.com/JFETs/LSK489appnote.pdf
https://www.ti.com/lit/ds/symlink/jfe2140.pdf?ts=1717672324923&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FJFE2140
https://www.st.com/resource/en/datasheet/tda7293.pdf
https://www.ti.com/lit/ds/symlink/tps7a49.pdf?ts=1717660447218&ref_url=https%3A%2F%2Fwww.google.com%2F
https://www.ti.com/lit/ds/symlink/tps7a3001-ep.pdf?ts=1717738722969&ref_url=https%3A%2F%2Fwww.google.com%2F
