TWO Sonic Imagery 995FET-Ticha Single Discrete OpAmp API style…..compatible with the VTV Amplifier Custom Hypex input buffer using two per channel, 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:
995FET-Ticha Discrete Operational AmplifierThe 995FET-Ticha is a high performance discrete operational amplifier designed for professional audio applications and areas where ultra-low noise, extremely low distortion and highly linear uncolored operation is required. A true super matched pair FET input stage is incorporated to provide superior sound quality and speed for exceptional audio performance. This in combination with high output drive capability and excellent dc performance allows use in a wide variety of demanding applications. In addition, the 995FET’s wide output swing provides increased headroom making it ideal for use in any audio circuit.The 995FET-Ticha opamp can be operated from ±10V to ±24V power supplies. Input cascode circuitry provides excellent common-mode rejection and maintains low input bias current over its wide input voltage range, minimizing distortion. The 995FET discrete op amp is unity-gain stable and provides excellent dynamic behavior over a wide range of load conditions.The all-discrete SMT design uses an ultra-precision differential matched FET 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 995FET-Ticha incorporates precision 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.
Dual matched pair temperature stable current mirrors, dual matched pair active current loads give the 995FET-Ticha it’s outstanding power supply rejection performance. The enhanced low distortion Class-A output driver stage can sink or source 250mA allowing this module to drive transformers directly. Integrated power transistor heat sinks coupled to a anodized aluminum enclosure keeps the 995FET-Ticha operating within a wide SOA and does not suffer from Beta droop when driving heavy iron or heavy loads. Each amplifier is fully tested and meets or exceeds published specifications.
Because of the 995FET-Ticha’s 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 and provides higher headroom compliance performance.
The 995FET-Ticha discrete opamp was designed as an enhanced upgrade replacement for the Millennia Media Series MM-99, MM990, Forssell Technologies JFET-993, JFET-992, or other similar end of life or obsolete FET based op-amp gain blocks. The pinouts conform to the 990/2520 package type, allowing direct replacement.
• Ultra Low Total Harmonic Distortion, 0.00048 THD+N @ 1kHz
• High Input Impedance Line Amplifiers and Drivers
1. When the best possible distortion performance is demanded. Most monolithic op-amps use Class-B or Class-AB output stages, and many of them (though certainly not all) show clear crossover distortion artifacts on the distortion residual. A discrete op-amp can dissipate more power than a monolithic integrated circuit (IC), and so can have a Class-A output stage, sidestepping the crossover distortion problem completely.
2. When the best possible noise performance is required. Super-matched precision matched pair field effect transistors can outperform monolithic IC op-amps, particularly with low source resistances. The most common examples are moving coil head amps, microphone preamps, summing structures in mixing boards, balanced cable line receivers and line drivers. These structures almost invariably use a discrete input device, with open loop gain (for linearity) and load driving capability provided by an ordinary op-amp which may itself have fairly poor noise specifications.
3. When a load requires more drive current, because of its low impedance, than a monolithic op-amp can provide without overheating or current limiting. Because discrete op-amps have high current drive capability, supporting circuitry impedances can also be scaled down within the application circuit. This will reduce the overall system noise, without increasing distortion and provide higher headroom performance.
5. When it is required to provide a low voltage supply to run a few monolithic IC op-amps. The cost of extra transformer windings, rectifiers, filter capacitors, regulators, and added complexity of powers supplies can be eliminated with the use of discrete op-amps.