Here is description from Sonic Imagery:

General Description:
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.

Features:

• Ultra Low Total Harmonic Distortion, 0.00048 THD+N @ 1kHz
• Ultra Low Noise, 1.1nV/rtHz
• High Current Output Drive (250mA into 75 ohms)
• 112dB Open Loop Gain
• +26.5dBu Output Levels (into 600 ohms)
• Standard Gain Block Footprint
• Operates over ±10V to ±24V supply rails
• Lower output offset voltage than existing counterparts
• Lower input leakage current than existing counterparts
• Class A Output Drive
• Particular emphasis on audio performance
• Designed, assembled and produced in the USA
• 3 Year Warranty

Applications:

• High Input Impedance Line Amplifiers and Drivers
• High Input Impedance Buffer
• Active Filters and Equalizers
• Summing/Mixer Amplifiers
• High Performance High Input Impedance
Instrument Preamplifiers
• High Performance A/D front end preamplifier
• High Performance D/A back-end driver


Why Use a Discrete Operational Amplifier?

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.

4. When a load must be driven to higher voltages than a monolithic IC can sustain between power supply rails. Monolithic IC op-amps are mostly restricted to supply voltages of ±5 to ±18 volts. Discrete operational amplifiers provide a viable alternative because they can operate in excess of ±24 volts.

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.

General Description:
994Enh-Ticha Dual Discrete Operational Amplifier DIP8The 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.
Model 994LV-Enh-Ticha, operates down to ±4.5V for low voltage applications.
Model 994HC-Enh-Ticha, higher output current drive applications.
Model 994FC-Enh-Ticha, Vishay Foil and TaN Resistors in drive stage option.
Contact us directly for additional options and pricing.


Features:

• Ultra Low Total Harmonic Distortion, 0.0003 THD+N @ 1kHz
• Ultra Low Noise 0.89nV/rtHz typical
• High Current Output Drive (150mA into 600 ohms @ ±24V supply)
• +26dBu Output Levels (into 600 ohms @ ±24V supply)
• Standard 8 pin DIP Footprint
• Operates over ±7.5V to ±24V supply rails
• Operating Current 17ma (each amp)
• Voltage Gain Open Loop 118dB
• Lower output offset voltage than existing counterparts
• Lower input leakage current than existing counterparts
• Particular emphasis on audio performance
• Designed, assembled and produced in the USA
• 3 Year Warranty

Applications:

• Low Impedance Line Amplifiers and Drivers
• Active Filters and Equalizers
• Summing/Mixer Amplifiers
• High Performance Microphone Preamplifiers
• High Performance A/D and D/A front end Preamplifier
• High Performance D/A I-V convertors
• High Current Buffer Amplifier

General Description:
990Enh-Ticha Discrete Operational Amplifier

The Model 990Enh-Ticha is a high performance discrete operational amplifier designed for professional audio application areas where ultra-low noise, low distortion and highly linear uncolored operation is required. It was designed as a high performance upgrade replacement for the Jensen JE990, Automated Processes Inc. API-2520, John Hardy Co. 990A-990C, FiveFish Studios DOA series, Seventh Circle Audio SC10, SC25, SC99, and Avedis Audio 1122 op-amp gain block. The pinouts conform to the 990 package, allowing direct replacement.

If the user is upgrading or replacing vintage or retro-clone gear, take note of the pin length required for your particular application. Older gear typically used modules with 0.480 to 0.510 inch long 0.040 pins. Sonic Imagery Labs offers this longer pin length variant at no additional charge. See the Model 990Enh-Ticha and 995FET-Ticha Mechanical Options Application Note AN-18 for mechanical details.

See table 1. below for additional discrete opamps which can be upgraded.

The all-discrete SMT design is similar to the JE990 basic topology but has been completely redesigned to use an ultra-precision differential super-matched transistor pair specifically designed to meet the requirements of ultra-low noise, ultra-low THD, highly linear uncolored audio systems. In addition to the enhanced input stage, the 990Enh-Ticha uses high 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 power supply voltage.

Dual matched pair temperature stable current mirrors, dual matched pair active current loads give the Model 990Enh 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 easily.

Integrated power transistor heatsinks coupled to a anodized aluminum enclosure keeps the 990Enh-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 990Enh 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.

Sonic Imagery Labs also can provide a variation of this model that can operate down to ±4.5V for low power low voltage applications. Contact us and ask about the Model 990LV-Enh-Ticha.

Features:

• Ultra Low Total Harmonic Distortion, 0.00045 THD+N @1kHz
• Ultra Low Noise 0.89nV/rtHz
• High Current Output Drive (250mA into 75 ohms)
• +26dBu Output Levels (into 600 ohms)
• Standard Gain Block Footprint
• 120dB Open Loop Gain
• Operates over ±9V to ±24V supply rails
• Lower output offset voltage than existing counterparts
• Lower input leakage current than existing counterparts
• Particular emphasis on audio performance
• Designed, assembled and produced in the USA
• 3 Year Warranty

Applications:

• Low Impedance Line Amplifiers
• Active Filters and Equalizers
• Summing/Mixer Amplifiers
• High Performance Microphone Preamplifiers
• High Performance A/D and D/A front end Preamplifier

Table 1. Compatible Upgrade Table
The Model 990Enh-Ticha can be used to upgrade and/or replace these obsolete or end of life discrete operational amplifiers. This list is by no means comprehensive. Contact Sonic Imagery Labs for additional information.

Jensen JE990 Series
Automated Processes Inc. API-2520, 2520H, 2525
John Hardy Co. 990A-990C
FiveFish Studios DOA series
Avedis Audio 1122
Seventh Circle Audio SC10, SC25, SC99
Sound Skulptor SK25, SK99, SK47
Yamaha NE80100, NE80200
TOA PC2011
ProTech Audio Model 1000
Purple Audio KDJ3, KDJ4
Modular Devices 1731, 1757
Modular Audio Products (MAP) 5000 Series, 1731 1731A
Melcor 1731
JLM Audio 99V
Inward Connections SPA690
BTI OA400
FAX Audio FA-100
Analog Devices 111

Why Use a Discrete Operational Amplifier?

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 pair discrete bipolar transistors can outperform monolithic op-amps, particularly with low source resistances, say 1000 ohms or less. 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.

4. When a load must be driven to higher voltages than a monolithic IC can sustain between power supply rails. Monolithic IC op-amps are mostly restricted to supply voltages of ±5 to ±18 volts. Discrete operational amplifiers provide a viable alternative because they can operate in excess of ±24 volts.

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.