Sony vFET Illustrated build guide

short review

my sony vfet amp has now more than 100h of burn-in time and i would like to share my impression of its sound.

first , i have to say that the most important factor of a sound system to me is how emotional a system plays and how the music touches me. this "feeling" is given when the sound of a system is a completely " rounded piece of work", despite all weaknesses of each individual unit in the system. so , fine-tuning of a set-up incl. the listening room is essential to me to "snap in" the sound;-)

i own different amps (transistor and tube) , but most of the time i listen with 2x SET 300b mono-blocks equipped with WE tubes. as pre amp i switch between two passive units; a TVC and a precision wire-wound potentiometer. my source is a nos dac running on batteries. the speakers (102 dbw/m) are open-baffle wide-range with additional horn-loaded dipole tweeters and active dipole sub woofers. the cables (mains and interconnects) are mostly silver. the whole system runs on its own mains separated from the rest of the house.

the sony vfet amp has received a nice base and i installed the chassis on 3 special feet similar to shung mook diamond resonators. ( to be honest i am not a fan of this hifi2000 housing that i am using now and i will replace it in the future with a self-made more suitable one ;-) )

some other chassis tuning steps were needed to balance and match the sound of the amp into the whole set-up. many different mains cable and fuses were tested to find the most suitable one for matching/integrating the amp into the system, etc.

findings:

- very natural sound colour / sound spectra

- excellent speed and timing

- it reproduces perfectly the "air" around the instruments and in the recording studio

- very natural and airy vocals

- the spatial rendering is excellent in all dimensions, especially in the depth. instruments in big orchestras are fixed placed and can be pointed deep in the hall.

- excellent base and low frequency texture

- surprising warm and soft sound for a transistor amp

- excellent dynamic in all frequency range. the "rise" and "fall" characteristic of the tone ( transient behaviour) is superb.

- very high resolution


just two remarks:

the sony vfet amp delivers in my system a bit less presented lower-mids. furthermore, i also look for a more "shininess / brilliance" in the highs. those aspects are more pronounced with my 300b. i have to admit that these attributes could be just because of the microphony effect of the tubes, never the less, these factors contribute to enjoy my music.

any way, i think these are also a question of fine-tuning and can be done with a suitable chassis/PCB resonance treatment, choice mains and interconnect cables, fuses , voodoo stuffs, etc. (for example, hifi tuning fuse corrected this unbalance in low-mids but i then missed the nice "soft" highs :) . excellent strong , dynamic , balanced and natural sound i could achieve with the combination of a shunyata anaconda mains cable and my diy silver fuse . however, the shunyata cable does not belong to me :-( and i prefer to enjoy the system using my diy stuffs ;-) ... :-D .... )

my opinion and conclusion: a beautiful amp! ... it competes/wins not only my 300b in most aspects but also many other high-end amps that i have heard! many thanks nelson and the force may be with you!
 
I finally received all the parts necessary for my near-silent DIY cooling solution. Two Noctua NF-S12A ULN fans, one molex to two 3-pin fan connectors and a 1 amp 12 volt power supply with a molex connector. I didn't realize when ordering it, but the power supply shipped from China so it took about 2 weeks to arrive. I wondered why it was so much cheaper than the rest of the same spec'ed ones. :rolleyes:

The only thing I hadn't worked out was how I was going to mount the fans to the chassis. Then it dawned on me to just secure them to the chassis with one of the hex bolt holes already on the back of the chassis on each side. I just needed to find hex bolts long enough now to go through the fan housing as the stock ones weren't long enough to go through the fans and still thread in. Luckily I had a couple laying around that ended up working. It's been running for about 30 minutes and I'm already down 30 degrees F. 105 vs 135 degrees F. The only thing I may do after this is spray paint the fans matte black so they don't stick out as much. Not bad for a less than $50 project.

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It does an incredible job at keeping my amp cooler. Much, much cooler. I think it's because they're cooling the heatsink fins directly. For reference, how many degrees does babysitter reduce the amp by?

Once I paint them matte black it won't be quite as ugly. Plus I'm normally the only person who sees the amp. My partner rarely steps foot in the room with my audio equipment.
 
I was joking ..... do your own - in your way , of course

I never measured , but I can estimate Babysitter is decreasing temp somewhere between 5 and 10C

difference between me being concerned and totally indifferent :)

Good to know. Before adding the fans I was reading 57C at the base of the heatsink, now I'm reading 37C. Ambient room temperature is 24C. Even though it's an ugly mod, I feel much more comfortable leaving the amp on for extended listening sessions now.
 
Well, fellow solder soldiers, I finished my Pass / Sony VFET amplifier and it sounds divine driving my ancient pair of Spendor SP-1's. It can get loud enough to annoy my wife, too. I know its related at 15 watts Class A into 8 ohms. Not sure I've seen rating where it clips, but I haven't found it in practice at any reasonable listening level.

Bias - my tech friend and I did this together and it really wasn't hard at all. We check all the resistances and then voltages set the driver bias and then set P1 and P2 at the VGS voltages written on the VFET's +1 volt. When we soldered the VFETs in and powered her up there were no pyrotechnics at all. Quiet as a church mouse with symmetric DC offsets of -0.4 Volts on both sides. We let her run for an hour and the bias drifted up a little, but not much. Judicious work with P1 and P2 got the DC offset below 10mV on both sides. (It is hard to to better than this with these 1-turn pots.)

it is a really sweeeeet sounding amplifier !!
 

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One other note - I am driving the VFET with a Broskie Aikido line stage with 6922's - gain of about 15. This is WAY more than the VFET needs. I can't get the volume past about 8:30 ! I would guess input sensitivity is less than 2V. Fortunately I'm using ALPS Black Beauties and I have a Black Beauty balance pot, so level tracking is not an issue. In any event, if you are using digital sources with a standard output of 2V, a Pass B-1 buffer stage should work just dandy with this amp.
 
and while you're changing these , to be fatter than speaker ones , route them separately (input vs. speaker)

move speaker lines bellow pcbs , leave input ones where they are , above pcbs

Zen - I'm using Kimber PBJ for the inputs - works fine. Outputs are 16 ga stranded wire with "bright colors". I routed high to avoid the power supply circuitry. Like I said the thing is quiet as Lenin's Tomb. Not sure I want anything to go under the PCB's.

I am also using a pair of IXYS Hexfred bridges - these are supposed to be exceptional quiet RF/EMI wise. They cost a little more (about $17 USD), but they have been excellent in every Pass project I have done, (Pearl 1, Pearl 2, FW F3, FW F5T, Sony VFET).
 
Zen, I have read too many of your posts ! I would NEVER call you a Do-Do ! :)

I routinely use 20 ga solid wire in my low voltage applications.....I just had this Kimber stuff laying around, so i used it here. It sounds pretty good as an interconnect. I can tell you there is no noise with this stuff. Now there may be more Divine Angels to be discovered in the signal, but the VFETs are pretty heavenly all on their own !