11-20-2018, 04:56 PM
(11-20-2018, 03:39 PM)Jibem a écrit : Réponse d'Alex Crespi . The Boss Himself
Can you tell me the interest of the "Kelvin-sense voltage feedback circuit" and should we put it on "sense set »?
It is for DC2 output only, and at present it is supported only by the MMK. It is a current/voltage feedback line that makes sure that 12V is always presented to the computer—at the end of the cable, really all the way to the output connector of the MMK board--regardless of instantaneous demand or losses from DC cable length.
Here is some more text about the JS-2’s Kelvin-sense circuit:
The pseudo-Kelvin-sense circuit of the JS-2's DC2 output:
The excellent 5-pin Micrel high-current, adjustable regulators we use have a voltage set pin. The JS-2 has a circuit to extend that line out over a thin coax cable so that a remote pair of resistors at the load can feed back to tell the supply what voltage to output. Being that it is at the load, it both eliminates the droop caused by normal length cable resistance (you could run 40 feet of cable and still have the exact desired voltage delivered to the load), and responds better to instantaneous current demands so that the voltage never drops.
When the small black slide switch on the back of the JS-2 is positioned to the right, "Sense Set"--towards the SMA coax jack of DC2--the supply ignores the output setting of the blue rotary switch (5/7/9/12V) and looks to resistors at the load for setting (which could be any custom voltage from 1.25V to about 13.5V).
Our original intent was to offer small "Sense Cubes" that would be just large enough to have an SMA jack and a DC barrel jack on one side, and a DC barrel plug (or jack) on the other side. Inside would be a very small PCB with various resistors and either a DIP switch or cuttable jumpers to configure for a variety of common voltages.
But right now the only product that takes advantage of the JS-2's sense circuit feature is our Mac mini DC-conversion/Linear Fan Controller Kit (MMK). The MMK has an SMA jack right next to its DC barrel jack, and the resistors are on the board. The JS-2 ships with a 5-foot SMA/coax cable and use of this feature is entirely optional (that is, the MMK can be used with other power supplies without using the SMA jack, and JS-2/MMK users don't have to use it either). What is fun is that if you have it hooked up and also put DC2's blue switch in the 12V position, you can, if you fingers are quick, switch between "Switch Set" and "Sense Set" while the music is playing and the Mac mini won't notice the blip or shut down.
Does the circuit have sonic benefits? Well, given that the JS-2 ships with one of my custom Oyaide/Belden 15awg, shielded, star-quad DC cables and that it is just 5 feet with not much drop on its own, and that a well set up Mac mini does not present a lot of fast current demand events, I don't find it to be a big deal in my system. It seems to help a tiny bit in the bass. But compare to the R-core transformer, the carefully balanced choke-filtered design and overall goodness of the JS-2 circuit, no the sense circuit is not a big deal.
Just to complete the picture with regards to the Mac mini, the JS-2, and the MMK, I will point out that our exclusive linear fan controller circuit of the MMK is a big deal as it rids the machine of the high-current (0.5A!) 12V, 25Khz pulse-train of the stock PWM fan-speed control circuit, and the benefit of that is easy to hear--even if you use some other external LPS or even an SMPS to power an MMK-equipped Mac mini.
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J'ai donc cru comprendre... que ça ne servait pas à grand chose...
Cela rappelle les premiers mac minis, ceux avec un lecteur cd et une alimentation externe de 18,5 v.
Un câble avec 2x3 connecteurs, ce qui permettait de pouvoir les enfiler dans n'importe quel sens.
En réalité 3 fils : +, -, et le fameux sensor.
Pour utiliser une alimentation DIY il suffisait de souder une résistance de 6,8 K entre le plus et le sensor, ou pas ...
Le texte du boss confirme tout de même que l'on peut se passer de la connexion au sensor.
Et ça, ça me permet d'avancer en attendant la réception du PCB MMK.
Merci à vous car je naviguerai moins à vue lorsqu'il faudra ouvrir la bête