F6 Amplifier
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lhquam
diyAudio Member

Join Date: Mar 2010
Location: Olalla, Oregon: Land of the 100 Valleys
That will not work properly because the two primary windings are seeing different voltages across them and will "fight" each other. Assume that the feedback node has voltage Vfb. The voltage across the upper primary is In+ - Vfb. The voltage across the lower primary is Vfb - In-.

If In- = - In+, then clearly the voltages across the windings are different unless Vfb=0.

If we believe that the total flux in the transformer is the sum of the contributions of the two primary windings, then the total flux will be proportional to (In+ - Vfb) + (Vfb - In-) = In+ - In- and the feedback has no effect.

Quote:
 Originally Posted by Zen Mod coffee is brewing , now ... so take this with grain of salt

Antoinel
diyAudio Member

Join Date: Jan 2012
Location: Pennsylvania
Quote:
 Originally Posted by Zen Mod I can't give you exact recipe , not having experience with exact Jensen type ; whatever - speaking strictly of xformer - loading each secondary with nominal impedance (150R) will result in better bandwidth be aware that Jensen guys made it exactly that way don't think even for a sec that Pa doesn't know that - he just took different approach - to correct entire amplifier , killin' seven flies with one blow 1938 - Mickey Mouse, Minnie Mouse - The Brave Little Tailor - YouTube
Mr. Pass and Mr. Zen Mod. Is there a transformer which will present a 20 KHz bandwidth in OLG F6, and will it improve performance of CLG F6?. The OLG F6 circuit is a specific and useful test method to find such a transformer. Plot OLG versus Frequency for each TUT.

 25th November 2012, 04:34 PM #3103 Nelson Pass   The one and only     Join Date: Mar 2001 No doubt there is such, but you are likely to find that some other parameter has been traded for it. Did you read the transcript of the BAF talk on the F6?
Antoinel
diyAudio Member

Join Date: Jan 2012
Location: Pennsylvania
Quote:
 Originally Posted by Nelson Pass No doubt there is such, but you are likely to find that some other parameter has been traded for it. Did you read the transcript of the BAF talk on the F6?
Thank you Mr. Pass. I'll read it slowly and carefully on your FW site. I have the weakness of speed reading.

N.B. Got the point. The Jensen in F6 is already a rarity per its writeup. Others which may push a higher OLG bandwidth will be unobtainium and prohibitively expensive.

Last edited by Antoinel; 25th November 2012 at 04:58 PM. Reason: Tweak

 25th November 2012, 05:05 PM #3105 Zen Mod   Official Court Jester diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain read here : 6moons audio reviews: FirstWatt F6 __________________ 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
Antoinel
diyAudio Member

Join Date: Jan 2012
Location: Pennsylvania
Quote:
 Originally Posted by Zen Mod read here : 6moons audio reviews: FirstWatt F6
Thanks Zen Mod. I also found it on the FW site. I will have to read it many more times to absorb it and fully appreciate its content. It is a very well written seminar/article. The writing style of Mr. Pass like his past articles flowed smoothly, was clear, and he loaded it with valuable present and future information. As written, it is a technical feast for the mind of DIYers.

lhquam
diyAudio Member

Join Date: Mar 2010
Location: Olalla, Oregon: Land of the 100 Valleys
The transformer coupling in the F6 feedback loop cause the phase of the 2nd harmonic to vary with frequency. Here are THD vs Freq and Phase vs. Freq plots for the F6 and the F5. Not how much greater the phase shift is for the F6, particularly in the mid frequencies.

I suspect that this changes the sonic signature of the amplifier.
Attached Images
 F6-thd-phase-sweep-p01.jpg (109.3 KB, 661 views) F5-thd-phase.jpg (107.5 KB, 636 views)

lhquam
diyAudio Member

Join Date: Mar 2010
Location: Olalla, Oregon: Land of the 100 Valleys
In my previous post, the F5 THD was so low that the phase change was totally determined by the MOSFET gate capacitances.

Here is the same F5 circuit with P3 adjusted for 0.025% 2nd harmonic. As you can see, the phase is essentially constant to 20kHz.
Attached Images
 F5-thd-phase-2.jpg (109.3 KB, 561 views)

 26th November 2012, 02:38 PM #3109 buzzforb   diyAudio Member     Join Date: Oct 2010 Location: Burlington, NC Interesting thing would be to listen to both circuits adjusted for similar harmonic structure and see if they sound the same. __________________ ...Shape the sound , Man!
lhquam
diyAudio Member

Join Date: Mar 2010
Location: Olalla, Oregon: Land of the 100 Valleys
It would be hard to adjust the F5 to have 3rd harmonic high enough or
to have the H2/H3 vs frequency at all similar to the F6.

What would be interesting is to see H2, H3 plots with phase for some vacuum tube amps with sonic signatures that are at all similar to the F6.

Quote:
 Originally Posted by buzzforb Interesting thing would be to listen to both circuits adjusted for similar harmonic structure and see if they sound the same.

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