JS-2 Linear Power Supply
$ 925.00
Dimensions: 9.0 inches wide x 9.1 inches deep x 3.3 inches tall (with feet).
Weight: 10.5 pounds; 14 pounds in its full double-box shipping cartons (shipping dimensions 14"x14"x9").
Warranty: 3-year parts and labor (excludes shipping costs after 90 days).
Made in U.S.A. Shipping anywhere in the world via Express Mail Intl. (EMS) or FedEx (custom-quoted deep discount rates by country; often less than than postal, plus faster and more secure).
Includes:
1 custom 5-foot DC cable. This special cable is a shielded, star-quad with 4 conductors of tinned, stranded 18AWG; paired at the connector that makes it about a heavy 15AWG. Gold/copper/brass Oyaide (5.5mm x 2.5mm) DC barrel plugs from Japan at both ends. Upon request we can terminate one end with a 2.1mm version of the Oyaide connector in case you need that size at the device end.
[A second one of these in-demand custom cables can be ordered by JS-2 purchasers for $75; Specify length and device-end termination.]
2-meter, 16AWG, shielded AC power cord (USA mains plug, but you can cut and attached an appropriate local plug; it is a good heavy and shielded cord, so adapting it is worthwhile.)
1 SMA coax cable for optional activation of JS-2's unique Kelvin-sense voltage feedback circuit (currently supported only by the UpTone MMK).
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John Swenson on the benefits of a choke-filtered linear power supply:
The traditional cap only filter (transformer, diode bridge, big cap) produces raw DC with a sawtooth riding on top. That sawtooth produces lots of high frequency components that the regulator has to deal with. Traditional regulators do very well at low frequencies, but have lousy characteristics at high frequencies which means a fair amount of those high frequency components from the cap-only filter get through to the regulator. Fancy discrete regulators do well at blocking the high frequency components, but add cost and complexity to a PS. Our approach is to use a properly designed choke-based supply whose ripple is a perfect sine wave, no high frequency components, thus a traditional regulator works very well. The discrete regulator is not needed to deal with the high frequency components, since there aren't any.
All diode types except Schottkys emit a burst of ultrasonic noise as they turn off. This noise can go forward into the load circuit AND it can go back into the AC line, and it can also excite the transformer resonance. The "slow" diodes still have this ultrasonic noise. Schottkys are the only type which do not have this noise. Schottkys also usually have about half the voltage drop of other diode types and are usually faster. Which type to use depends a lot on what your supply looks like and what you are trying to optimize for.
With a traditional low voltage design with a large cap right after a bridge you get large current spikes, these produce a large amount of high frequency noise which needs to be filtered by what comes after the cap. In this type of circuit the slow diodes can help cut down on the extent of the high frequencies generated by the sharp high current pulse. BUT they still generate the ultrasonic noise.
This is another reason why we like to use the choke-based design. With the choke there is no steep high current pulse, so no disadvantage to Schottky diodes. You get the advantage of no ultrasonic noise, lower voltage drop (so lower power consumption in the diode) and no big massive current pulses.
