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Old 16th September 2012, 12:44 AM   #1891
lhquam is offline lhquam  United States
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Not a chance. The amplifier already has rather low open-loop gain. Reducing the bias to 0.1A would drastically reduce the FET transconductance and open-loop gain. Nothing left for feedback to reduce the distortion.

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lhquam: I hope that you have the curiosity to forsake Class A operation of Teaser-6 for several days [it is in the bag], and operate it in Class AB mode. Drop the idle bias to 100 mA, and tell us how it sounds by comparison with its established Class A. Noting that the old Classic operated in Class AB and some of its other renditions in Class B, and they sounded great too. This is also an open challenge to Mr. Pass, and Mr. buzzforb and others to move away from this default Class A. Show us that Conceptual F6 sounds great operating in Class AB first, and then its expectedly better sound as Class A. This is a [the] challenge you may wish to face. Afterall, most amplifiers sound their best in Class A!
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Old 16th September 2012, 01:45 AM   #1892
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For me, distortion is good enough where it is unoffensive, so my preference is for second harmonic.
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Old 16th September 2012, 02:24 AM   #1893
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I have not been closely following this thread. Does the F6 go into class B?
The JLH definitely does not. It does 1.5 x bias, then current clips
What does the F6 do?
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Old 16th September 2012, 02:58 AM   #1894
lhquam is offline lhquam  United States
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It runs fine Class-AB, but with the expected deficiencies. Here is Spice simulation with 4 ohm load, 50 watts, 1kHz. THD was 2%.

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I have not been closely following this thread. Does the F6 go into class B?
The JLH definitely does not. It does 1.5 x bias, then current clips
What does the F6 do?
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Old 16th September 2012, 12:28 PM   #1895
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Pa just posted article
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Old 16th September 2012, 12:33 PM   #1896
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Quote:
Originally Posted by lhquam View Post
It runs fine Class-AB, but with the expected deficiencies. Here is Spice simulation with 4 ohm load, 50 watts, 1kHz. THD was 2%.
F6 and its clones [Teaser-6, Franken6 etc.] are/seem to be destined to operate predominantly Class A and gracefully beyond it into AB. Open loop gain [OLG] emanates fully from the output stage JFETs. This is unlike the Classic based on BJTs whereby OLG has contributions from the front end and the output stage; with a possible voltage step-down [ OLG control?] by the interstage transformer.
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Old 16th September 2012, 12:54 PM   #1897
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Old 16th September 2012, 01:43 PM   #1898
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Quote:
Originally Posted by lhquam View Post
Not a chance. The amplifier already has rather low open-loop gain. Reducing the bias to 0.1A would drastically reduce the FET transconductance and open-loop gain. Nothing left for feedback to reduce the distortion.
Thank you for responding and your analysis. Teaser-6 conforms to another facet of the Pass Principle; the only source of gain emantes from the least # of gain devices; the output stage JFETs. Please calculate OLG and %THD for 0.13 A bias current and compare with those due to 1.3 A bias you use in Teaser-6. Thank you.
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Old 16th September 2012, 03:18 PM   #1899
lhquam is offline lhquam  United States
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You should download LTSpice (free) and Do It Yourself, after all, DIYAudio is the name of this collection of forums.

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Originally Posted by Antoinel View Post
Thank you for responding and your analysis. Teaser-6 conforms to another facet of the Pass Principle; the only source of gain emantes from the least # of gain devices; the output stage JFETs. Please calculate OLG and %THD for 0.13 A bias current and compare with those due to 1.3 A bias you use in Teaser-6. Thank you.
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Old 16th September 2012, 04:07 PM   #1900
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You should download LTSpice (free) and Do It Yourself, after all, DIYAudio is the name of this collection of forums.
Thank you for your advice. Will do.
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