| 1-24 pieces $65.00 ea | 25-50 pieces $60.00 ea | 50 pieces $55.00ea |
The JFET992 is a 1.10" x 1.10" x 0.50" potted module containing a Class A, all Discrete JFET amplifier. This module is compatible with the industry standard discrete opamp footprint which includes the John Hardy 990 and API 2520 modules.
At Forssell Technologies we refer to the JFET992 as a second generation design because to our knowledge, only one other Class A, discrete JFET opamp is available commercially, and we designed the original version of that circuit. While that old design met our design and evaluation criteria 5 years ago when we designed it, after building thousands of them we have applied what we learned about that circuit and improved upon it both subjectively and objectively in this new design. The result is the JFET992 amplifier, with better measured performance (objective) and improved sonic quality (subjective).
The JFET992 uses 8 large source geometry JFET transistors and one NPN transistor (for DC control). Unlike our first generation design the JFET992 is differential throughout. It has the standard opamp topology's differential input ports and a single output port. Techniques are used within the JFET992 to reduce the input capacitance, however no cascode amplifiers are used. The result is an amplifier with a very simple signal path that has wide bandwidth (-3 dB at >2 megahertz), high slew rate > 60 V/us, and fast rise time (150 nanoseconds). The JFET992 is extremely linear and does not require large amounts of feedback to obtain acceptable performance. There are no internal compensation capacitors used in the JFET992. A small value compensation capacitor across the feedback resistor may be needed for stable operation at closed loop gains below 6. The use of high transconductance JFETs also results in low input noise. Vishay, Holco, and Beyschlag metal film surface mount resistors are used throughout the JFET992. A single resonate point bypass scheme is used for onboard power supply bypass (no external bypass caps are needed, however for sonic reasons external electrolytic capacitors are encouraged).