DIY Sony VFET Builders thread

Is anybody interested in purchasing my round #1 lottery amp? I’m just looking to get what I paid for it ($525) and whatever it costs to ship. Honestly, it’s a superb amplifier, but I have a few superb amps and I find the Sony collecting some dust. Makes more sense to pass along to someone who’ll get more use out of it.

I have a strong preference to stick with a buyer in the US, but am open to shipping wherever - just know that you’ll be paying whatever shipping costs and assuming all the risk.

If you’re interested, please send me a PM. I’ll go based on the order I receive them. Replies in this thread won’t count.

ps. I realize a post like this makes more sense in the swap meet, but I wanted to give dibs to those in the Pass forum.
Very cool! Did the internet just slow down as your inbox began to fill up?
I just brought my VFET back into rotation. This time with my current SLOB dipole speaker project originally inspired by Mr Pass’ creation. The speaker is 4ohms nominal passive crossover (waveguide planar tweeter, 5in PA paper cone mid, 8x 6.5in woofers in slot loaded open baffle array and a U-baffle) but 91.5dB sensitive. I am driving with SMSL SU-9n DAC and my own hybrid preamp with 12dB gain. I had some doubts that it could drive 4 ohms but is handling it marvelously. I have never heard such SPLs or bass from the VFET before. The soundstage is airy and floats above the speakers. There is a delicacy in the vocals that the Class D amps could not match. I’m enjoying it a lot.
Yep, for us guys who like to swap amps often, it is the only way to go. I also have an amp A/B switcher box so that lets me choose between at least two amps on active duty pretty easily. On amps with a front panel VU meter it is a harder decision.

Years ago, I remember reading about how Google desgined their own server farm rack mount computer chassis. They simply put the business end facing out so cable access was easy. I think they maintained RAID drive hot swap on this same end as well. Only the power cord was on the "back". Nowadays, i think many server racks follow this trend.
For sure triodes will make a very transparent front-end (unless you take a triode with a metal case of course, or a Nuvistor).

Does anyone have experience with driving the V-FET 2SJ28 follower using a triode front end? Pushing a bit like < 5 V RMS, I never go above a watt or two.

I just made a new ECC82 preamp and I could not be happier. It is based on an EAR circuit by Tim de Paravicini that I modded a bit using positive feedback to suit my purpose, based on ECC82/12AU7 (in fact, I used 5814 and 12BH7).
Simulation shows Low distortion. Fine square wave at 10K/9V RMS. Low output able to drive even the full gate capacitance of > 1 nF (as a follower, gate cap of the 2SJ28 is reduced to hopefully < 20% of the value)
So I thought to make another one, now using 6SN7 for dring the SIT. And put that in the V-FET box . .


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Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Does anyone have experience with driving the V-FET 2SJ28 follower using a triode front end? Pushing a bit like < 5 V RMS, I never go above a watt or two.

2SJ28 is easy to drive, but you want to check the high frequency rolloff for the VFET input capacitance. For the approx. 150 pf, it will rolloff at about 100 KHz with 2500 ohm source impedance (I am using the data book figure). I expect that you can scale this with whatever the plate value of the Triode is.

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More than 100kHz is not practical. So I’d add a gate resitor anyway. A 6SN7 as cathode follower might even have an output impedance of below 400 ohms …
Or drive it from a big triode from the anode directly, say 10Y. Choke loaded for instance. 800 ohms. Lots of ideas. It should be possible. :cool: Some of these tubes have a warm sound. That should not be pronounced.

My 2SK182 as common drain is marvelous, forget all comments like it sounds like a tube. I have the 300B SE amp too. On paper the curves might look similar, but the SIT is such a dream to listen to. I use it too for the high output impedance (I took a ‘filter’ from the current-drive paper for my Fostex).