Threshold's 1982 technical information sheet devotes an entire page (of three) just to the model FET one. Here are the specs:
phono section:
Distortion: Less than .01% at 5 volts preamp output into a 10 kOhm load
high level section:
Distortion: same as phono section
Slew Rate: 25 volts per microsecond
Rise Time: 2 microseconds
Supply Rejection: -80 dB
Overload Point: 14 volts preamp output peak
Preamp Output impedance: 470 Ohms.
Enjoy your new preamp.
phono section:
Distortion: Less than .01% at 5 volts preamp output into a 10 kOhm load
high level section:
Distortion: same as phono section
Slew Rate: 25 volts per microsecond
Rise Time: 2 microseconds
Supply Rejection: -80 dB
Overload Point: 14 volts preamp output peak
Preamp Output impedance: 470 Ohms.
Enjoy your new preamp.