Charles, do you have the schematic for the HTAA-16W-A ? The KO4BB mod has limited info
Tnx Jerry k1...@arrl.net -----Original Message----- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Charles Steinmetz Sent: Wednesday, August 31, 2016 4:49 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Anybody want a Thunderbolt power supply? Nick wrote:> > I’m going to shoot for <= 35 mV P-P. If you need better than that, > then it probably turns into a hybrid switching+linear system It's been years since I played with Tbolts (as opposed to just using them), but as I recall there was no possibility whatever of getting the best results from any switching supply without at least one stage of linear "polishing." In fact, everything I tried with initial switching regulation benefitted from two levels of linear polishing. It was my conclusion that starting with a switching supply of any sort is a bad idea. I found that for best performance the -12v supply, which feeds the DAC, needs to be about 1000 times better than what you are shooting for (i.e., low tens of uVp-p). That surprised me, because I assumed there must be some internal regulation of the DAC supplies -- but it was what my testing showed. Sure, a Tbolt will work with dirtier power than that, but for real time-nuts performance I consider an all-linear supply with an ultra-low-noise -12v rail to be absolutely necessary. Since that is not very hard to provide, I see no reason to try to make do with less. One low-cost solution is to wait for a cheap Power One HTAA-16W-A triple-output power supply to show up on ebay, and do a very minor modification to raise the +12v current limit (so it will handle the first moments of a cold start without current limiting) as detailed here: <http://www.ko4bb.com/getsimple/index.php?id=download&file=06_Misc_Test_Equipment/Power_One/Power_One_HTAA-16W-A_mod_for_Thunderbolt_power_supply.pdf> That approach achieves excellent results -- close to the best you can do -- with very little fiddling. If one wants the very best performance, the -12v supply can be adjusted down to -16v or so to provide the headroom to add a ULN regulator or a capacitance multiplier. (The Tbolt only draws a few mA from the -12v supply, so the ULN regulator can be a suitable op amp with no external pass transistors.) Last time I bought them, I paid $25 for a lot of three HTAA-16W-A's. Best regards, Charles _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
