Legendary Nelson Pass Threshold SA/1 - one of the best sounding amps ever made. These monoblock amplifiers are spectacular. If you're a fan of the Threshold Stasis design by the legendary Nelson Pass, then you probably know all about them. These particular amps have had all their power supply filter capacitors upgraded to new ones and with larger capacitance. The original Mallory caps were 29,000 microFarads, the upgraded capacitors by Cornell Dublier are 37,000 microFarads (see the photo), There are four power supply caps used in each of the two monoblocks (8 total). Combined capacitance in each upgraded monoblock is 148,000 microFarads. The capacitor upgrade is a noticeable sonic improvement particularly in the lower bass notes, very deep and tight. In parallel with the electrolytic capacitors are 4 added audio grade caps with lower ESR, the result is improved high end detail and transients. Another upgrade was done to each mono block amp by replacing the factory original five-way brass binding posts. The larger gold plated ones maximize power transfer to your speaker cables, while minimizing signal loss due to contact resistance and oxidation. These amps are very liquid sounding and tube like, when I listen to them I just marvel at how great they really sound...they truly do sound phenomenal. I've listened to them connected to a tube preamp, a Pass Labs X2.5 preamp and a Threshold FET10/e preamp...I think the tube and FET10/e preamps make the best sounding combo, although the Pass Labs X2.5 is pretty close. Needless to say both these mono block amplifiers perform flawlessly with no pop, hum, or hiss. There are two flaws to mention - on one of the amps the power meter works intermittently, some times it works, other times it sticks. Also, that same amp has an abrasion mark on the front bezel that I've tried to capture in one of the photos. Because of this, I rate that one amp at 6 out of 10 cosmetically, the other amp is conservatively rated 8 out of 10, just due to slight imperfections from age but nothing major. Each amp weighs just under 80 lbs. Serial numbers are consecutively numbered and each amp was manufactured in 1986. The workmanship and impressive construction is evident by the oversized heat sinks, thick aluminum front face plate & bezel and machined handles. Each amp operates in "pure" Class A mode, so the transistors are continuously forward biased even at idle (hence the massive aluminum heat sinks to dissipate unused speaker power as heat energy). But with the high quality Motorola output transistors as current drivers along with the general over design of the electronics by Nelson Pass and Threshold team, the effort that went into creating such a work-of-art without compromise is most evident by the pure audio and detailed musical sound they produce. These amps are not that common, and needless to say, haven't been produced since 1988. For the buyer, I will double box each amp separately to ensure safe arrival. Both amps will be shipped FedEx and insured. Depending on shipping distance in the continental US, the lowest FedEx rate could be upwards of $125 each. Alternatively, if the interested buyer is in the San Diego area, a local listening audition and pickup is encouraged. (Copyright droderiv8350ci September 2017)
Below are the factory specs for each amplifier:
Rated power: 160W into 8 ohms, 300W into 4 ohms. Current capability: 40A continuous, 60A peak. Frequency response: 7 Hz - 100 kHz, +0/-3dB Voltage gain: 26.5dB. Input impedance 75k ohms. Dimensions: 19" W by 8¾" H by 19" D. Weight: 78½ lbs.