This is a hand-crafted, point to point wired, Fairchild 670 clone compressor/ limiter. The SR-71 is the brainchild of Larry Janus, of Tube Equipment Corp. These amazing recreations are no longer manufactured because they are just too expensive to make (and to sell reasonably). This unit is serial #002, and is one of only a handful made without PC boards (all point-to-point wiring). In brief, the original Fairchild schematics were used as the basis for this design, but the frequency specifications of the SR-71 are a bit better, due to the use of modern, super high-end (and pricey) Sowter input/output transformers. The comp sports 17 vacuum tubes, MASSIVE power transformers, huge Sowter audio transformers, and a TUBE power supply (just like the original Fairchild 670)!! There's more to be found online, if interested. Suffice it to say, this is a unique and rare piece of analog heaven. NOTHING compares to the sound of this era of compressor/limiter design and build. 45 pounds of Creamy, warm, glue - Beatles in a box. Hate to let it go, but I'm not doing enough music production to justify holding on to it. $5200 (or best offer).
More info from company website:
What we copied exactly. What we didn’t: We have chosen to use the original Fairchild 670 basic circuit, with the exception of employing a more plentiful pair of 6BQ5/EL-84s instead of 6973s as sidechain output tubes, a 6L6 as a high voltage regulator, and a far more available quartet of 6BA6s per channel as vari-mu tubes in lieu of the scarce or prohibitively expensive 6386s. We also use a big power transistor to control the DC filament voltage of the 8 6BA6s. The plate curves of the 6BA6s wired as triodes are virtually identical to the plate curves of the original 6386s when viewed on a tube curve tracer.
In addition to the above, several release times (1,2,3) have been shortened, for more flexibility with percussive material. 2 is the new 1. The complexity and loss of gain made us choose not to implement the “Lateral-Vertical” matrix.
Sowter Transformers are used in the audio path. They are Mumetal shielded and isolated from the chassis for superior hum rejection. Their use results in a flatter frequency response than the original 670 transformers in the region between 10kHz and 20kHz. This allows more usefulness in mastering and mix bus applications. An original 660 or 670 is typically several dB down by 20kHz.
At 44 lbs. it’s a very substantial piece of equipment, and very true to the original circuit in virtually all aspects. And, it’s only 4 Rack Units tall!
