F6 Amplifier

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#4,441
Antoinel said:
US 4,107,619 [inventor Pass] gave us STASIS [R] technology, and its THRESHOLD power amps. Gain devices are both cascoded and the fluctuation of current flowing through them is minimized. The gain of the [amplifying] device is now almost constant, and this transistor is highly linear in action. There is a schematic which will add more transistors to your application. Nothing is really free.

I find it interesting that your work is minimizing THD which has sonic benefits in Pass diy amps. The ultimate in THD reduction is/maybe SuSy. There is a patent and schematic for it too.
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I do not think that Nelson pursues ultimate low distortion. IT seeems he pursues low distortion with minimal circuitry.
 
#4,442
Antoinel asked whether I participate here. Maybe yes, maybe no. I do visit from time to time to stay abreast of goings-on but I rarely post. That's because I'm passive, not active (not a DIYer who builds anything, just a reporter on other people's work which kinda defeats the whole focus of this site). But anyone is always welcome to contact me thru my site if they have specific questions about my reviews. I try to answer every email I get. Unless it gives away millions, solicits sex or pharmaceuticals or wants me to invest in some time share in Barbados -🙂
 
#4,447
labjr said:
I wonder if there will ever be a successor to the F5 which is buildable by the masses with available parts.
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Get yourself a pair of 2N5460/2N5457 -- match 'em up -- the pin orientation is different from the K170/J74 and transconductance lower -- but you can get THD under 0.01% and the noise isn't noticeably different as the gain in the first stage is only 20dB.

While the 2N5457 may be difficult to find at times, it is easily substituted, and the SMT version is in production.
 
#4,448
Srajan Ebaen said:
Antoinel asked whether I participate here. Maybe yes, maybe no. I do visit from time to time to stay abreast of goings-on but I rarely post. That's because I'm passive, not active (not a DIYer who builds anything, just a reporter on other people's work which kinda defeats the whole focus of this site). But anyone is always welcome to contact me thru my site if they have specific questions about my reviews. I try to answer every email I get. Unless it gives away millions, solicits sex or pharmaceuticals or wants me to invest in some time share in Barbados -🙂
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Thank you for replying. Your reports are also highly valuable to audio DIYers too. The objective measurements by Mr. Pass, your reports, and the collective reporting of DIYers who built Pass diy amps paint the most accurate performance picture of the gear under study.

I could not find your report on F6 which generg talked about in an earlier post.

Best regards.
 
#4,450
ichiban said:
6moons audio reviews: FirstWatt F6

😉
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Thank you ichiban. Mr. Ebaen is gifted. His F6 report is rich in writing style, and is impressive in its analyses and comparisons. Truly remarkble. Made me think to visit his site periodically and read all sorts of interesting reports.



Said Mr. Ebaen, and my possible connections to be taken with a grain of salt:
  • F6 damped the music more so than SIT. generg, his perception of relative damping may be because of the lower output impedance of F6 than that of SIT [4 Ohms].
  • Surprisingly, Mr. Pass used negative feedback in F6. Without NF, the power bandwidth of the attendant current source amp is unacceptable, and the amp's output impedance is high.
  • F6 sounded SIT-ish. I like to call negative feedback in F6 as Pass Feedback. It emanates from a high output impedance port and terminates at a summing junction. Schade has exploited this similar approach earlier to convert the characteristics of a pentode to those of a triode. SIT is intrinsically triode-sounding. F6 is a remarkable SIT mimick .
  • The output stage of M2 is comprised of complementary MOSFETs operating in the common drain configuration; absent feedback. Thus this amp has a low intrinsic output impedance of 0.4 Ohms. Can readily implement the classic Black feedback; but not Pass. M2 is a different amp. Its topology is interesting.
Best regards
 
#4,452
Zen Mod said:
M2 is not having any significant OLG to have any significant CLG

to be precise - its all in OLG :rofl:
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M2 is a simple and potent topology. The familiar 2SK/2SJ front end and the auto transformer make an interesting preamp. Let this preamp drive a complementary pair of MOSFETs operating in a common source configuration, or an opposed drains which has relatively high output impedance. Apply Pass negative feedback from this high output impedance port to the gates of the front end [summing junction]. Now one has a modified M2 with triode-like characteristics; instead of the pentode characteristics in the parent M2.

The top of the auto transformer may also drive a SIT. The phase inverted output of the SIT is then fed back to the gates of the complementary JFETs to further lower the output impedance of SIT and decrease its distortion. The front end preamp of M2 has great potential.
 
#4,455
Antoinel said:
M2 is a simple and potent topology. The familiar 2SK/2SJ front end and the auto transformer make an interesting preamp. Let this preamp drive a complementary pair of MOSFETs operating in a common source configuration, or an opposed drains which has relatively high output impedance. Apply Pass negative feedback from this high output impedance port to the gates of the front end [summing junction]. Now one has a modified M2 with triode-like characteristics; instead of the pentode characteristics in the parent M2.

The top of the auto transformer may also drive a SIT. The phase inverted output of the SIT is then fed back to the gates of the complementary JFETs to further lower the output impedance of SIT and decrease its distortion. The front end preamp of M2 has great potential.
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even connected in autoformer fashion , including xformer in feedback loop can be tricky business
there lies Pa's witty - how he connected FB in F6 and xformer isn't in FB loop
 
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#4,458
naah

just tried (clumsy) to make distinction between cases - where F6 is having sort of diminutive voltage swings through xformer , where M2 have full voltage swing exactly through xformer

I didn't make proper analysis or sim of phase behavior , but I have feeling that position of feedback signal inclusion point in F6 is not so troublesome , as in case that FB signal inclusion point is anywhere in original signal chain going to top of primary

call me ZM Lazy Susan on Lazy Sunday ...... but no brain for more

:clown:
 
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