Sonic Imagery Dual Discrete DIP8 OpAmp……compatible with the VTV Amplifier Custom Hypex input buffer, but may be used in other amplifiers as well. These are an excellent upgrade from IC based opamp designs.
Here is description from Sonic Imagery:
994Enh-Ticha Dual Discrete Operational Amplifier DIP8
The 994Enh-Ticha is a dual high performance discrete operational amplifier designed for professional audio applications and areas where ultra-low noise, low distortion and highly linear uncolored performance is required. It was designed as an performance upgrade replacement universal dual op-amp gain block.The 994Enh-Ticha Discrete OpAmp achieves a new standard of excellence in noise performance with 0.89nV/Rt.Hz@1kHz noise. This ultralow noise is combined with excellent high speed specifications (gain-bandwidth product >50MHz), immeasurably low distortion output, and true precision parameters (>200µV offset voltage, 118dB voltage gain open loop). Although the 994Enh-Ticha’s input stage operates at nearly 1mA of collector current to achieve low voltage noise, input bias current is typically less than 1uA.
The all-discrete SMT design utilizes an ultra-precision differential super-matched transistor pair specifically designed to meet the requirements of ultra-low noise and ultra-low THD audio systems. In addition to the enhanced input stage, the 994Enh-Ticha uses high performance temperature stable power supply independent current sources. Supply independent current sources allow the bias to remain locked at the optimum operating point regardless of supply voltage or temperature.
Dual matched pair temperature stable current mirrors, dual matched pair active current loads give the Model 994 it’s outstanding power supply rejection performance. The enhanced low distortion Class-A output driver stage can sink or source 150mA allowing this module to drive transformers or headphones directly if required. Each amplifier is matched for noise, offset and distortion to within 0.1% of each other and both amplifier channels meet or exceed published specifications.
The 994Enh-Ticha op amp is a true bipolar op amp and behaves as such. It does not require a flying ground lead as do other designs on the market. It is a true drop-in replacement upgrade. Because the 994Enh is a true op amp, it can also be operated in single supply applications as long as external biasing has been implemented correctly.
Because of the 994Enh high current drive capability, supporting circuitry impedances can be scaled down within the application circuit. This can reduce the overall system noise, without increased distortion. The 994Enh-Ticha Discrete op-amp voltage noise is less than the thermal noise of a 50 Ohm resistor. Therefore, even in very low source impedance transducer or audio amplifier applications, the 994Enh-Ticha’s contribution to total system noise will be negligible.
The pin outs conform to the standard 8 pin dual in-line monolithic IC package, allowing direct replacement. See table 1. on page 6 of data sheet for typical monolithic operational amplifiers which can be upgraded.
Sonic Imagery Labs also can provide custom variations of this model.
• Ultra Low Total Harmonic Distortion, 0.0003 THD+N @ 1kHz
• Low Impedance Line Amplifiers and Drivers