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 2nd March 2013, 12:57 AM #251 diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain you are THD-less ........ What's the Buzz? __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
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Quote:
 Originally Posted by Zen Mod I didn't had impression that Pass was talking about sweet spot , in static context there is no THD in static
Zen Mod. I agree. My writing was not clear. Static meant idling diy F6 first at 1.5 A. Then let the amperage move up and down a transfer function to express itself because of the signal. The function [performance ]is linear and symmetrical up [to higher amps] an down [to lower amps] from the center point of 1.5 A . This linearity is expressed as % THD. It was determined by Mr. Pass and lhquam [beforePass loop feedback] to be an impressive value of less than 0.1% in his article on F6.

Question for Dr. Mazzola. What is expected % THD of the transfer function which is attendant to the device [any of the shown 3 DUTs] moving down along the trajectiry to 0.5 A from 1.5 A and then moving up to 2.5 A for a sine wave?

 2nd March 2013, 01:40 AM #253 diyAudio Member   Join Date: Jan 2008 Location: Southern California I have been following along,but i am a bit confused with the transfer characteristics and the sweet spot. Isn't it the case that if the application is a class a PP like F6 then the sweet spot is not as critical due to 2nd h cancelation and for Single ended the sweet spot should be found ridding on the desired loadline? Alfredo
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 Originally Posted by avincenty I have been following along,but i am a bit confused with the transfer characteristics and the sweet spot. Isn't it the case that if the application is a class a PP like F6 then the sweet spot is not as critical due to 2nd h cancelation and for Single ended the sweet spot should be found ridding on the desired loadline? Alfredo
Thank you avincenty for responding. Please keep in touch. Schade or Pass feedback issues are forthcoming. Forgive me; but I hope that those who are more experienced and know more than I, can address your question. Maybe it helps to recognize that a stand- alone device can have a sweet spot [e.g. Mr. Rothacher's L'Amp a simple SIT amp ] by inspecting its transfer curve/function. What happens when it is assembled into an amp with other devices is your valid question.
Best regards

 2nd March 2013, 02:09 AM #255 diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain it seems that this 3-part article series is like Pulp Fiction everything will suddenly fall in place , after reading last part however - I think that Semisouthfan is not a guy who can answer your question , at least not right now . Mithrandir can - he's the one who tortured poor F6 ( and entire family ) with pillow and comfy chair torture ( in some circles known as with brain augmented AP something ) __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
 2nd March 2013, 02:17 AM #256 diyAudio Member     Join Date: Oct 2010 Location: Burlington, NC Otherwise known as Moby. __________________ ...Shape the sound , Man!
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Quote:
 Originally Posted by avincenty I have been following along,but i am a bit confused with the transfer characteristics and the sweet spot. Isn't it the case that if the application is a class a PP like F6 then the sweet spot is not as critical due to 2nd h cancelation and for Single ended the sweet spot should be found ridding on the desired loadline? Alfredo
That's my simple understanding, but what do I know? As ZM points out, I haven't even listened to an amp yet. But lurking in all of this (from my analysis) is at least some linearisation from traditional forms of negative feedback. How much requires pushing the pencil.

 2nd March 2013, 03:11 PM #258 diyAudio Member   Join Date: Oct 2003 You can look at even harmonics cancellation as 100-100=0. Or would you not rather aim at 10-10=0 ? Patrick __________________ xen-audio.com
 12th March 2013, 04:44 PM #259 diyAudio Member     Join Date: Jul 2005 Location: North East Does anyone really know about the GaN devices? Are they similiar to Sic? How might a GaN device perform compared to an R100? Are there any available to try? Also possibly, is a GaN structure suitable to create a SIT device? Thx __________________ "It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
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 Originally Posted by flg Does anyone really know about the GaN devices? Are they similiar to Sic? How might a GaN device perform compared to an R100? Are there any available to try? Also possibly, is a GaN structure suitable to create a SIT device? Thx
At the risk of my comments becoming obsolete quickly, GaN, based on my team's attempts to get it, is mostly at the pre-commercial stage. The quasi-exception is EPC. By "quasi" I mean the rated voltage levels are too low to be a competitive alternative for SiC in switching, but for audio? Maybe. Looking at performance, EPC has two products that might be replacements for the R100: the EPC2012 and the EPC2015.

The EPC2012 has a rated Rds(on) of 0.1 Ohm, so this is the obvious first choice to consider. Alas, this is definitely NOT an R100, as the power dissipation is limited to 10 W at TC = 25 C, which must be derated to accommodate realistic heat sink temperatures. Maybe a preamp candidate. Availability is the bright spot. You can apparently buy some from inventory at DigiKey. Cost is bearable in absolute terms, but maybe pricey considering it appears unsuitable for a power stage.

The EPC2015 has a much lower rated Rds(on) but a drain current rating more like an R100. The power dissipation is still light, though, at 30 W before derating for realistic heat sink temperature when compared to 114 W for the R100 at TC = 25 C. The limited drain source voltage of 40 V might not seem too big a deal, but this is around where some amps are operating. And beware, a warning of how rugged (or lack thereof) this GaN on Si technology is can be measured by the highly unusual rating just under the traditional absolute maximum voltage rating on the data sheet: the transistor can handle "up to" 10,000 48-V, 5-ms pulses at 125 C. That's a nice way of saying EPC does not know what will happen to their device if you exceed the voltage rating. And, as the whole wide bandgap community knows, the rating at VDS = 40 V is a knock down from the design value to accommodate uncertain reliability of this inherently defective material technology. On top of that, DigiKey lists zero in inventory, casting doubt on the actual availability "score" for the EPC2015.

There are several other credible GaN suppliers out there, and not everyone is taking the highest risk approach of GaN on Silicon like EPC. But availability is uncertain at best because they are restricting release of data, let alone parts, to the general public. That may change in coming months and certainly in the next year or two for at least one provider that I have better insight into; but one can never be sure until it happens.

Lastly, the basic GaN transistor technology is the High Electron Mobility Transistor or "HEMT" also known as the "HFET" for heterojunction field effect transistor. They are commercially proven for RF (cellular phone base stations, for example) but that is mostly GaN grown on SiC, NOT silicon. Anyway, this transistor is similar in ways to the lateral form of the JFET known as the MESFET, but because it is a heterojunction structure, the similarities fall off quickly. SIT like properties are not inherent to the lateral HEMT to my knowledge.

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