austinpop Posted May 12, 2018 Share Posted May 12, 2018 22 minutes ago, auricgoldfinger said: I popped an SR blue quantum fuse in my JS-2 today and like the result. To be very clear, the JS-2 is perfectly fine with the stock fuse. For many people, there are higher priority areas in the audio chain that should be addressed before upgrading a fuse. If you have already upgraded the fuse in your DAC and are chasing the last bit of performance out of your system, then the SR blue quantum fuse is something to consider for your JS-2. What amp rating is needed on the JS-2, Brian? My Audio Setup Link to comment
austinpop Posted March 15, 2019 Share Posted March 15, 2019 On 3/13/2019 at 2:18 PM, Superdad said: I recently realized how conservatively we rate these (we quote it as 5-7 amps). Had one on the bench the other day running continuous 8.2 amps (!) at 12V (with 120/240V AC mains input; lower AC input lowers max current at 12V). Was not even hot. Hi Alex, I'm glad to hear that these units are selling like barely-warm-at-8.2A cakes. Actually I had a serious question set of questions for @JohnSwenson and you. It has to do not with continuous current, but peak current. Can you compare and contrast how a "conventional" LPS like the JS-2 handles very short current peaks vs. the LPS-1.2? What I'm really wondering is how high a current peak can each sustain, given a short enough duration? Can each deliver 2x, 3x, even 10x the sustained current rating, or is there a practical limit where even for an infinitesimally small interval, max current is limited to some value? Is the amount of headroom - let's define this as rated peak/rated continuous - different for the JS-2 vs. the LPS-1.2? Apologies if this has been answered before - a few searches that I were unfruitful. My Audio Setup Link to comment
Popular Post austinpop Posted March 15, 2019 Popular Post Share Posted March 15, 2019 17 minutes ago, Superdad said: Hi Rajiv: That's a great question. And while neither the choke-filtered JS-2 or the bank-alternating UltraCap LPS-1.2 can be considered "conventional," the physics of peak current handling are quite the same for both--other than that the paralleled LT3045 regulators in the LPS-1.2 are faster--and fairly in common with other power supplies. Yet the actual answer turns out to be far more complex than your simple question would make it seem. I just got off the phone with @JohnSwenson about it, and I think it took hime 20 minutes to explain to me. All sorts of factors, not the least of which are the duration of the current-demand spike, the inductance of the cable (lower is better), the capacitance after the regulators (larger can potentially allow for higher current but dramatically slows the supply down), and the peak current limit of the regulators. I know that is not an answer, just a list of a few of the factors. The true answer would requite plotted graphs and many hours of measuring for just a subset. Perhaps John will have some time to elucidate a bit to give folks a better sense of the topic. But based on what he explained to me, I would be very wary of power supply manufacturer claims of giant peak-current capability. Believe me, I would love nothing more than to state that the UltraCap LPS-1.2 can handle brief (10-50uSec) peaks of 4A (it might) and that the JS-2 can handle 20A spikes (it might not). But things are never so simple... Hi Alex, Thanks for the clarifications. It would help if I knew what I was asking precisely - which I don't! Perhaps part of my confusion comes from a perception that may be incorrect, that the LPS-1.2 has a "cliff" at 1.1A, so that led me to wonder if instantaneous current demands in excess of 1.1A would be tolerated, and if so, by how much. I am starting to feel more and more that an PSU's sound quality can be variable and heavily depends on the operating point (%utilization of rated max) one chooses. While I haven't done any rigorous listening experiments, I think there is some merit to the idea of massively overprovisioning a PSU for its intended application, so you are running at <50%, perhaps even <25% of capacity. Of course, too often we don't have that luxury. AudioDoctor and spotforscott 2 My Audio Setup Link to comment
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