Sony vFET Illustrated build guide

[Joca]

An externally hosted image should be here but it was not working when we last tested it.

can't get GND-T18

Maybe it's because the JFETS are matched at 9.0ma. In the guide said that in the range of one miliamp it would be fine.

 

[Joca]

my error...and a big one....i forgot to solder the j313 and k2013.....what a stupid thing to do....meanwhile...i can get the right voltage on T18 but only if i adjust P4. is it ok?

 

[Rodeodave]

I was about to say, your Q5/Q6 look like they're not turned on...

So with Q5 and Q6 now installed, what's your T6-T7 and T8-T9 voltage drop?

 

[Gyuri]

Assumed you have P3 P4 initial settings was fully counterclockwise, you need to set them slowly, one after the other, always just a little bit, while watching voltages T6-T7 and T8-T9. If you have reached 1.2V on them, you are fine.
You can watch meanwhile G-T18 voltage, it must be near 0V.
Don't worry if it not exactly 0V.
Just do it everything, as it is in building instructions.

 

[Joca]

The voltage T6-T7 and T8-T9 is 0.230v.
It has to be 0,0?

 

[Gyuri]

No, they must be 1.2V.
But you need to set P3 and P4 to achieve this.

 

[Joca]

Maybe i am not that far on the guide because i am only checking the voltages and it sais that T6-T7 must be 0. I just dont know if at this point it has to be 0,000vdc.

 

[Gyuri]

I think it is a good starting point.
As far I remember, I never had 0V in this position.

 

[Gyuri]

I think, I understand your problem.
You have stopped on page 7, where table says, T6-T7 and T8-T9 must be 0V.
Please read next page, and go on!

 

[Joca]

Yes. Thats the case. Thank you. I will proceed later and post the results and pictures. Im going with dual monos.

 

[Gyuri]

Don't hurry, read the manual instead.
So are you a piano teacher?
My parents were in this business.
My father was a college music teacher, choir leader.
My mother was a solfeggio teacher, introducing small people into the world of music.
Many of them later became famous Hungarian musicians.

 

[Rodeodave]

You need to bias up the frontend, yup. This is described in part 3 of the article. This is done WITHOUT the VFETs installed.

When the frontend bias is set, proceed to part 4.

 

[Joca]

Don't hurry, read the manual instead.
So are you a piano teacher?
My parents were in this business.
My father was a college music teacher, choir leader.
My mother was a solfeggio teacher, introducing small people into the world of music.
Many of them later became famous Hungarian musicians.

Really? Nice!

Im teaching piano but i have a passion for electronics and specially for the various aspects of sound. This is a hobby that my father gave me. He was and is a very curious person with no academic knowledge in the analog electronics world but that was the trigger point for me to enjoy music and later to pursue the piano lessons. Well, im going farway with this offtopic theme. Im going to proceed with the build. Im anxious to listen to this baby vfet.

BR

 

[Gyuri]

Well, I don't think we would be off topic, because what we trying to achieve, it is for music, most of all.

 

[Joca]

Yes, indeed. You are right!

 

[Joca]

well, everything went fine till now. Just one question. I've biased one channel in the first 5 minutes after power on. I could get 100mv across R32 and almost 0 offset (1mv). The amp is warm now, after 40 minutes and the voltage drop is at 97,2mv and offset ~5mv. Should i rebias to 100mv? or leave it?

 

[Zen Mod]

think

what is percentage ?

 

[Joca]

3%. The guide says the values drift a little with temperature. I "think" that 3% is not considerable but...what do i know!?

 

[Zen Mod]

just leave it as is

what's always critical - DC offset on output - for home amps , everything up to 50mV is in range of normal

for PA amps that's up to 100mV

so , you're good

 

[Joca]

thank you...always learning!