DIY Sony VFET pt 1

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wdecho

Member
Joined 2014
Doubtful but possible.. They are being made but only for military's purpose and not for the public. That is what I have read and heard. The only purpose specifically would be audio and there is such a small demand most would not spend the money to do so. From what I understand the small run Nelson had made years ago cost him 1/2 million dollars.
 
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woofertester

Member
Joined 2011
I ran across a researcher who developed some SITs for defense applications in the 1980s. I believe that the specific equipment was RADAR but that is just my guess. There are publicly available papers about SITs from this era.

As was stated above, these devices do not show up in the commercial market. If they are still being made, they are used for classified purposes.

Every commercial producer of SITs has discontinued the parts. Obviously, there is not enough demand to keep a wafer fab busy in perpetuity.

There are surplus parts available now that I have curve traced and they are genuine triode curve parts. KP926, 2SK60, 2SK182ES. There were some 2SJ20 p-channel parts on eBay but they sold fairly fast. I grabbed some while they were available.
 
chede

chede

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Joined 2016
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A big thank you from me also to you, Nelson and everybody who worked on this !
I will wait a few more weeks and wish all of you who are participating now the best of luck.

As I am lucky to have two pairs of 2SJ18 / 2SK60 and a pair of spare THF-51S, I am looking forward to the next design versions and the more generic chassis, even if it might take a few months :)


Best regards, Claas
 
RafaPolit

RafaPolit

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Joined 2016
Http://rafaelpolit.com
I'm wondering, is there a list of products that used the VFets mentioned? I am wondering if I can go cannibalizing old hardware from friends and family, but with the pandemic, there is little chance of visiting everyone. Maybe someone or somewhere has compiled a list of models that used them?

A google search only throws a lot of people claiming to sell "the real thing" for various prices. But not models that included the part.

Thanks!
Rafa.

edit: Or can someone just post one such model that used it so I can search similar models or of the same period?
 
E

edmararj

Member
Joined 2011
Super_BQ said:
In my experience for deburring holes, these step drill bits don't have the right angle. I much rather use the larger larger sized drill bit that has a steep angle so it removes the burrs closer to the surface. This is especially important when drilling holes in thin sheets of say 2mm or less.

@raduschka

I've spent a long time building tube amplifiers and found that if you want authority and slam of the transistor power amp, you need to have deep pockets. It's a reason why tube types like the 211 and 845 are way out of reach for the average audiophile enthusiast. I find the VFet offers the best balance in the triode sound form. No hassles with filament noises / hum from tube amps. Ultra long life (no worry of tube degrading because of too many hours racked up), much safer due to lower working voltages (if you have young children around).

I also don't expect the VFets will go for snob pricing like NOS 300B Western Electrics. Even certain small signal tubes like NOS 6SN7 go for well more than what a single Sony VFet would sell.
Click to expand...

Hi Super_BQ,
There is an alternative to the drill with a variable diameter to make the hole for the XLR connector. It is manual punching punch for sheet metal, like this:
https://www.amazon.com/Sheet-Metal-Punch-Manual-Knockout/dp/B0793S5WM1
Edmar
 
xrk971

xrk971

Founder of XSA-Labs
Joined 2012
etsy.com/shop/XRKAudio
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I have a question regarding front ends for this amp. If it is nominally rated at 10w and 8ohm, that’s 9Vrms (25.5Vpp) required to reach full output. Most +/-15v rail preamps can swing +/-13v easily. Could one simply connect a preamp/headphone amp to drive the power output stage and skip the various stock front ends? In this sense, any number of discrete or opamp based preamps can be used easily.
 
Mark Johnson

Mark Johnson

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Joined 2011
Paid Member
@xrk971, the right person to answer your question is Nelson Pass. Between now and whatever time he answers (IF he answers), I recommend you read the second half of Nelson's post #484 in this thread. It suggests that your intuition from BJT emitter followers and MOSFET source followers, may not be entirely applicable to VFET source followers. The "hybrid pi model" of a VFET has a vastly different ro than the hybrid pi model of a BJT or a MOSFET.

truly wonderful lecture notes from UC Berkeley -- and it's a 100 level course! Wow

Or just take a look at the Marauder front end schematics, and notice that some ignatz has used an OPA552 opamp (max allowed rails: ±30V) and a DC-to-DC voltage up-converter, to drive the gate of the VFET.



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xrk971

xrk971

Founder of XSA-Labs
Joined 2012
etsy.com/shop/XRKAudio
Paid Member
Mark Johnson said:
@xrk971, the right person to answer your question is Nelson Pass. Between now and whatever time he answers (IF he answers), I recommend you read the second half of Nelson's post #484 in this thread. It suggests that your intuition from BJT emitter followers and MOSFET source followers, may not be entirely applicable to VFET source followers. The "hybrid pi model" of a VFET has a vastly different ro than the hybrid pi model of a BJT or a MOSFET.

truly wonderful lecture notes from UC Berkeley -- and it's a 100 level course! Wow

Or just take a look at the Marauder front end schematics, and notice that some ignatz has used an OPA552 opamp (max allowed rails: ±30V) and a DC-to-DC voltage up-converter, to drive the gate of the VFET.



_
Click to expand...

Thanks for the clarification. I will take a look at the post you suggested. Maybe what we are talking about is closer to a low impedance headphone amp output that can drive the VFET gate. I am actually working on one with dual OPA551’s (similar to 552) and also OPA547.

Nice lecture notes from a course at Cal - those were some fun days....
 
rayma

rayma

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Joined 2011
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6L6

6L6

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Joined 2010
Paid Member
Itsmee said:
It's only my opinion so worth nothing; to coin a phrase, 'The only good SMPS is a dead SMPS' :rofl:
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You haven’t been playing with modern ones then...

The Vfet amp (well, mine anyway, which uses the exact same parts that will ship in the kits) is, absolutely, positively, without any doubt in my mind, the quietest amplifier I’ve ever heard. Every amp until this would have some very faint rushing noise if you put your ear directly up to the tweeter or midrange. So quiet that you can’t hear it once your ear is just centimeters away from the dome or cone. That’s my subjective baseline for a quiet amp.

With the inputs shorted, ear as close to speaker as you can get, the Vfet is indistinguishable with power on or off. It’s amazing.

Good switchers are going to take a bigger and bigger part of this space and I am honestly looking forward to it. :)
 
Super_BQ

Super_BQ

Member
Joined 2001
rayma said:
Tools like this are very useful.
https://www.amazon.com/Deburring-Go...cphy=9018920&hvtargid=pla-1066670698501&psc=1
Click to expand...

Have never used such a tool but I doubt it. I'm partial to the sharp edge of a cutting tool, like the sharp edge of a larger drill bit and cordless drill works good enough. For extra large holes like for the XLR openings, I use the straight edge of a hand sculpturing tool used in autobody work.

@ 6L6: Yes SMPS have come a long way. About 20 years ago hifi guru Jeff Rowland? was a big supporter of SMPS in his line of high end Class D amplifiers. My guess he was just trying to carve a niche market at a time when there was so much anti-SMPS in high end audio.

My concern is the transients. How fast are SMPS at the low end response vs large storage banks of capacitors served the job quite well. Reminds me of Class A vs Class B - how fast are the response to the quick dynamics music has?
 
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