DIY Sony VFET Builders thread

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Dennis Hui

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Joined 2002
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Bart,

For reference, Variac posted a BOM for the 2016 diyaudio vfet project (two vfets per channel):

https://www.diyaudio.com/community/threads/sony-vfet-amplifier-part-2.276711/page-139#post-4991406

You should verify things from the original article: https://firstwatt.com/pdf/art_diy_sony_vfet.pdf

(Note a number of the parts in Variac's bom are no longer available or are currently out of stock, but a lot of subs are available.)

BTW, there is a build thread for that project here:
https://www.diyaudio.com/community/threads/sony-vfet-illustrated-build-guide.302380/

Good luck with your build.

Dennis
 
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711JAM

Member
Joined 2021
I have the the Sony PVFET OS 2 boards almost done, I do have 'another' question. On the schematic OS 2 R 1and R 2 are .47 ohms. The kit supplies .84 ohms resistors. Do they have to be .47 ohms? thanks in advance.
 

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triode_al

triode_al

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Joined 2004
Depends on the transistor. With 2SJ18, take 2x.47; else with 2SJ28 take 1x .84. And a short in the second position of R2.
(I have .82 because that was in my box (the kit i got assumes 2SJ18) and I complemented it with .12 to get the original total of 2x .47 value; but I know I deviated from practice.)
 
ItsAllInMyHead

ItsAllInMyHead

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I'd ask a few things in addition...

1) Is the amplifier in the picture the p-channel VFET offered as a kit mentioned in post #1 of the thread?
2) If so, did the extraordinarily-skilled builder of the amplifier choose to wire their speaker binding posts differently than the build guide for their own reasons?
3) If I have a P-channel VFET amplifier built per the guide... should I connect my adapter in the manner shown in the picture?
 
xrk971

xrk971

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Cauwil said:
Hello,

How did you wire TRS phone jack to speaker cable adapter ? I can see some resistors.

Thanks
Click to expand...
I have two 220ohm 1W resistors wired from Ring and Tip to Sleeve (GND) to provide a small high impedance load for the amp - this is mainly to drain the DC offset from capacitor coupled outputs so I don’t get a big pop when I plug in the headphones for the first time. Other than that, the TRS jack is wired Ring to right and Tip to left and Sleeve to GND (per usual convention for TRS stereo).

Some people like to use 22 ohm or 47ohm or similar resistor in series to reduce the signal getting to the headphone. I don’t have that.

Be careful with DC coupled outputs as a single turn on thump or pop can destroy a sensitive headphone or earbud just like that.
 
MEPER

MEPER

Member
Joined 2017
Is the input impedance of the P-channel version more or less defined by the 3 x 1 MEG resistors in parallel (R2, R3, R5)?
So 1 MEG / 3 approx.?
This is a very easy driven power amp? ......more easy than many pre-amps?
I have a DAC which can be set to "pre-amp" mode (instead of fixed output). Then vol. will be controlled in digital domain (company claims it is loss free). It seems to work well. Probably because the VFET amp is easy to drive. I just wanted to experience the VFET as pure as possible. It is also the most silent setup I have experienced.
 
MEPER

MEPER

Member
Joined 2017
I use a Cambridge DacMagic 200M. The digital preamp vol control may only be "bit-perfect" for 16-bit music......but I don't now how it is implemented.
If there is a small loss for 24-bit music they will probaby claim that it is still better than using an analog solution.
The VFET amp it self is very silent and I can't hear any added noise using the DAC as pre-amp. The RCA out from the DAC is standard 2Vpp or so. It seems sufficient for my 94 dB speakers to play load enough.
I have just switched to this setup from using a real pre-amp so I do not have a final verdict yet :)
 
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oltos

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pfarrell

pfarrell

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Joined 2019
thussfarrell.com
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oltos said:
A friend here built his own version of a Sony VFET amp and raves about, especially driven by this preamp.
https://glass-ware.stores.turbify.net/ainost.html
https://www.tubecad.com/2018/03/blog0415.htm

What amazes is me is how people here and probably lots where else can continue to build Sony VFET amps when production of those transistors ended decades ago.
Click to expand...
Aikido is fantastic...IMHO. I can't wait to try it with VFET—when I finish them!!! Certainly a great preamp though with several other FW offerings... like M2X.
 
A

Antealta

Member
Joined 2020
TungstenAudio said:
more details...

When I decided to build a linear power supply for my VFET amp, I chose to keep it a bit smaller and simpler than my usual amount of DIY overkill. I also wanted to keep its size in a nice proportion to the chassis that was designed especially for this amp. This led me to purchase a pair of Triad Magnetics 160VA toroidal power transformers, VPT30-5330, on which to base the unit. These are just the right size for the Sony VFET amp. After a few hours of being left on, they are warm to the touch, but not hot.
To realize the best potential of the amplifier, I knew the PSU needed to be a full dual-mono design, and have very low noise and ripple. My success with the "SLB" capacitance-multiplier supply in my F6 indicated that the single-rail version would probably be a good way to go. This is a relatively compact PCB that fit well in the smaller chassis that I wanted to use. As it uses the LT4320 synchronous rectifier, it also makes the most of the power which the smaller toroids will deliver. As I did with the supplies in my F6, I made some different choices for the output transistors in the Szklai pair, intended to keep them in a more linear region of operation while allowing for a lower dropout voltage. Eventually I also had to re-tune the RCRC control network at the base of the control transistor to allow easier adjustment of the output voltage at 1.7A current delivery.
The power supply has its own warm up time before it reaches it final voltage, but happily that is less than the warm up time of the amplifier. The two running together need an hour or so before making the final adjustments. That is pretty typical of other FW amps with linear supplies, so no problem.

So far I haven't added any bulk capacitance to the output of the SLBs. With my F6, I found the extra bulk capacitance was necessary to get the very best performance. With the Sony VFET, I find its overall tonal balance to be just right with the amp as-is. If I were to make a change, it would be to lower the value of the signal coupling capacitor in the front end of the amp from 1000 uF to 440 uF, or even 220 uF. Then I would add a Kemet ALS70 series 24,000 uF, 63V electrolytic for each power rail inside the VFET amp chassis. This combination would have the dominant pole of the amp set by the supply capacitance, not the signal coupling cap.


The inside of the VFET amp was only altered to remove the SMPS ripple filter that is common to both channels. I left the Panasonic 1000 uF caps in place on the individual output stage boards. Nothing else in the amp signal chain has been altered as yet.
Click to expand...
Hi

I have a Vfet pt2, and i am building the linear power supply

I have ordered the pcb from XRK audio

do you have a bom of the changes on your build, the output transistors and re-tune of the rcrc.
And real any help i can get
Thanks
Andreas
 
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