DIY Sony VFET pt 1

[ggetzoff]

That was a very common response on the other Nelson Pass class A power amp project which had a bunch of different, interchangeable front end cards: The diyAudio First Watt M2x

I estimate that around 40-50% of the people who built an M2x, used the front end card designed by Nelson (called "Ishikawa" in the M2x-osphere) and never built or tried any of the other possibilities. Not even the front ends whose PCBs were automatically included as part of the M2x board bundle shipped by the diyAudio Store. Of the folks who did try other cards, it appears that most of them found one that they liked best of all, and usually it wasn't Ishikawa. That may not be a shocking outcome, since Ishikawa was only one out of eight competing front end cards. A diversity of personal tastes, and idiosyncratic preferences among the builders/listeners, naturally results in a wide distribution of final choices. They likes what they likes, as Popeye the Sailor Man would remark.

Mark,

That is certainly human nature. When I read that someone dismissed a design or device (or tube, for that matter) I always ask if they tried different operating points and did they measure distortion.

The salient point is that the hobbyists has to know what their taste is and how it is created: one cannot discard a device or design until experimentation of operating points is exhausted. Then, and only then, will you know that it will never be your taste.

Cheers,

Greg

 

[ggetzoff]

that's why invented Beauty Factor Resistor position, in upcoming concoction

and mein Groß Bruder Generg (sort of) invented Zen Amount Pot, applicable in some Papamps

life is fun, so why not making Audio the same .....

Choky,

Good point and I behold much in your beauty........

 

[Zen Mod]

Choky,

Good point and I behold much in your beauty........

oh yes, it's already well known, that I'm like that , all around my Gorgeous Body and Mind

here goes Zardoz picture, imagine it, don't have it handy to attach

 

[ggetzoff]

Yes....let’s just keep it at that!

 

[Nelson Pass]

I’m trying to wrap my little brain around some of the design characteristics and put it in perspective with the other VFET amp designs that were offered and what I have built and listened to so far (ACA-with Semisouth @Q1 and F2J).

Let me know if I have any of it correct and what insights anyone may have.

This offering is a common drain follower. Which means it would normally offer current gain like the F2J except that the front end Papa designed for it will provide voltage gain via a transformer?

The F2j is a common source design. The previous Sony vfet projects were common drain like this one, but push-pull. The choices were narrowed to this by scarcity of parts and the desire for consistent results.

 

[planet10]

just noticed: the cool chassis does not have a switch on the front? not very practical, especially if one stacks two on top of each other. Ok, back to the drawing board.

I like the power switch on the back. An amp like this shoule be on 7/24 when in use.

dave

 

[rottalpha]

The F2j is a common source design. The previous Sony vfet projects were common drain like this one, but push-pull. The choices were narrowed to this by scarcity of parts and the desire for consistent results.

If it will sound anything like the SIT-3, this new amp is already a winner

 

[ggetzoff]

"MOST of the magic" ahh, to think about what could have been... had I just won the lottery.. but now stuck with second fiddle... for all eternity... so sad..

Tokin devices are still to be had, possibly. I just bought a couple of sets, one from Prasi.

Sell thf-51s 2SK182ES NEW NOS to-79 SIT v-fet, from Japan TOKIN

 

[pinholer]

Thank you, Mr. Pass, for this generous offering. It will be felt by many people.

Good luck to everyone in the lottery. Even if you don't win, remember that we, the members of diyAudio, have already won the big lottery in life.

As for the new amplifier, I think that I've already had a bit of a preview of it, although indirectly, as the last amplifier that I built uses basically the same output stage design. I have several SIT amps and this one is my favourite. 2SK82 -2SJ28 SE Amp

 

[tidybearm]

hello, is it possible to bridges mono amp to gain more power?

 

[Nelson Pass]

Yes, but you will end up with a different sound via cancellation of 2nd harmonic.

 

[tidybearm]

thank you

 

[Thomaudio]

Something similar. Details of mounting, biasing and such. The Tokins being N channel parts would look more like part 2 of this project, where the polarities are reversed. One interesting result for N channel follower is that you don't have to reverse polarity twice to get the 2nd harmonic phase negative.

Big upside is the potential for more power.

Just wondering if the Tokin devices are as linear at the Sony? Any idea of how much more power is possible? Many thanks!

 

[Zen Mod]

linear enough, to make big honkin' bada$$ amp, in whatever topology you want

 

[Mark Johnson]

I have uploaded schematics, parts lists, PCB Gerbers, and Mouser "one click" shopping carts for the four optional input cards, in the thread linked below. Please enjoy!

Scourge, Bulwark, Marauder, Dreadnought "front end" cards for DIY VFET amp

 

[jschmonsky]

P and N difference

Does anyone want to explain the difference between the P and N versions.

 

[overtheairbroadcast]

Difference in polarity.

Page 3 bottom 3 paragraphs of the attached pdf in post number 1 explains it.

 

[Nelson Pass]

Just wondering if the Tokin devices are as linear at the Sony? Any idea of how much more power is possible? Many thanks!

The Sony parts seem made audio and 8 ohms. The Tokins seem to prefer a
different impedance, although running at higher dissipation and/or adjusting the surrounding circuits will generally cover the difference.

You can even use feedback. Or so I hear...

 

[res07njc]

Some load line tidbits there. Good stuff. If you play with the Sonys, you'll see "8 ohms", typical volts, being perpendicular against the gain of the parts, generally. At least thats what I've noticed. Other parts have different curves, sk60, pass-sit.... not so talked about.

 

[WBS]

Any chance of getting a replacement deluxe 4u faceplate with the vfet logo?

Unfortunately, no. I already asked the powers that be.

However I designed a pretty cool faceplate for my 4U that pays homage to Nelson, SONY and the VFET. It is printed, not etched. If you're interested, shoot me a PM and I'll share it with you. I suspect that Gianluca probably still has the file.