Sony vFET Illustrated build guide

6L6

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Sure! The Vfet front end is basically the same front end as the BA-3 with a cascode to protect the Jfet from the higher voltage rails.

I’d just use a BA-3 FE, as it skips the cascade and has placement for the output cap on the PCB, and you get the addition of the P3 potentiometer.
 
FINALLY found time to finish my vfet amp. After installing the vfets and reading through the article on the firstwatt website one last time I fired it up.....and had less than 50mv across R32 on both sides, as well as less than 50mv offset at the output. It was almost too easy. I only had to slightly tweak P1 on both sides to get offset close to 0. The pots are MUCH more stable with the vfets in. In all seriousness, I'm concerned I'm somehow missing something, because it was so stable on first power on. R32 is 18mv...ish on both sides ( ready to be brought up to 100mv ), offset at the outputs +- 10mv - never more. Going to check the front end values one last time then hook it up to some cheap speakers for a test run.

Any reason not to proceed?
 
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There is something special about how it sounds. I won't waste anyone's time trying to describe it, but I like it more than my F4. And I love the F4.

My BA3FE preamp now officially has waaayyy to much gain...so fixing that is next on the list.

Are you using linear pots on your BA-3? Try changing to audio pots if so before making changes to pre. Zen posted the changes needed when I asked the same question on another thread but changing from linear to audio pots solved it for me.
 
It's an Alps blue velvet 20k. I'm almost certain it's a log pot. My speakers are 93db ish. With the ba3fe ( exactly built as original schematic, full gain ) driving the f4 antthing approaching half way on the volume knob was really loud in an 800sf room. Pre driven by schiit modo multibit ( 2v rms iirc ).
 
Hi - hoping to get a little help with this. I am building and powering up one board at a time. I have the Antek trafo that gives 22VAC. That is giving me 30VDC at the input to the connected board. Problem is with about half of the voltages I am getting exactly half what I should be - like I have lost a + or - rail somewhere. The voltages I am getting (compared with what I should be getting) are below in brackets.

Note that I have the full kit with the supplied parts. I carefully installed the resistors previously and checked all the readings using the procedure for them and all those readings were OK. No VFETs are in yet.

POINTS VOLTS (Actual Volts)

G – T6 +28V (15.06)
G – T8 -28V (-14)
G – T4 -24V (-14)
G – T2 +24V (14)
T6 – T7 0V (0
)
T8 – T9 0V (0)
T6 – T11 ~ 5V (7.2)
T8 – T13 ~ 5V (7.2)
G – T18 less than a few +/- volts (17mV)
G – T14 +13V (6.8)
G – T15 -13V (-6.8)
G – T19 ~+12V (11.88)
G – T20 ~-12V (11.88)
G – T17 ~-10V (9.7)
G – T16 ~+10V (9.7)

Any ideas on where to look? I have checked for solder bridges on the board - no issues there. Should I first be looking for a dodgy component or perhaps a bad solder join?

Thanks