This is a Threshold SL-10 preamplifier. This was one of Threshold's very highly acclaimed full function preamplifiers. The unit was designed by audio legend Nelson Pass and John Curl (phono section) and competed with the best of Mark Levinson, Audio Research, Conrad Johnson and Krell in its time. Full function includes moving magnet (mm) and moving coil (mc) phono capability. The phono section of this preamp handled my 0.24 mV output cartridge without issue. The preamp also has a full tape monitor loop. Total inputs number 5: phono, tuner, Aux 1, Aux 2, and the tape monitor which can technically be used as an input.. The tape loop means there are a total of 8 sets of RCA inputs and outputs. This preamplifier was one of the first units to employ a separate power supply.
The preamp has been fully upgraded with the following changes:
All electrolytic capacitors in the preamp module were changed for Panasonic FM and Nichicon Muse capacitors, considered among the very best for audio applications
Key resistors in the phono and line stage sections were changed to Vishay VTA (best in the world$$$$)
The 14 pin op-amp was also upgraded
The volume potentiometer was replaced with a far superior Stepped Attenuator
Electrolytics in the power supply were replaced with high quality units of higher capacitance (this went up from 13,800 mF to 24,000 mF) then bypassed with Wima film capacitors
All inferior sounding tantalum capacitors were replaced with audio grade polystyrene, polypropylene film and bi-polar units!
The overall sound of the preamplifier improved in every area of the audio spectrum. Bass is deeper and tighter, sound staging is much more detailed and vast, midrange has more transparency and liquidity and the highs are extended and smooth. This audiophile preamplifier would cost upwards of $3k today and it is ready to provide another couple of decades of enjoyment to the next owner.
If your in the Los Angeles area you are welcome to come by to demo this Classic Gem and hear it hold its own against my other 5 Digit reference preamplifiers