Sony vFET Illustrated build guide

[Zen Mod]

Pass

 

[Soundhappy]

I will be using K60 and J18 VFETs. Is it satisfactory to measure the Vgs using a Peak Atlas DCA75 or am I better to use the approach diagrammed by Mr. Pass?

Your all V-FET's have the same T-54 rank.
Imho Mr. Pass DUT diagram is more close to real work condition of the amplifier.
Make them hot for 15 minutes , temperature stabilise on the heatsink
then take Vgs measurements.

Sony VFET Amplifier Part 2

Greetings

 

[Soundhappy]

Sony VFET Amplifier Part 2

Sony VFET Amplifier Part 2

Sony VFET Amplifier Part 2

You can use two 19 Volts laptop psu's connected together for bipolar
(-) (0 Volts, center tap ) and (+).
Two bench lab psu's ( current limited 1A max ) are always great tools.
My setup on the pictures

 

[hirscwi]

Pass

I appreciate your economy of language!

 

[hirscwi]

@soundhappy, I love your picture... it's worth 1000 words.

Thank you for the links. I'm excited to make this amp. It will be the most complicated that I've built.

 

[Dennis Hui]

This is an excellent amp and well worth the effort.

Have fun with your build.

 

[AnthonyA]

Anybody can give idea
Will this amp work optimal with 8 ohm 89 db jbl L166? Reasonably loud level



Thank you

 

[6L6]

Absolutely

 

[AnthonyA]

Schweet.. Thanks Jim

 

[Jim50hertz]

Correct.

Q1 n-jfet k170
Q2 p-jfet j74

NPN for Q3 and PNP for Q4, so
ZTX450 for Q3 and ZTX550 for Q4

I can also confirm that Q5 (left position when looking at the pcb) must be P channel, so either 2SJ313 or FQP3P20. Q6 (right position) must be N channel, so either 2SK2013 or FQP3N30.

RodeoDave thanks for this. I'm ready for the first stage of power up.

Just to double confirm, on the ZTX450/550, the round side is the side with the writing on it?

 

[Jim50hertz]

Ok, so I was able to confirm orientation from datasheets, where I should have gone in the first place!

I've powered up both boards, and with 510r in r34/35 I get around 4.7v across both r34/35 on both boards.

How do I ascertain Jfet idss from this and adjust r34/35?

My voltages are way off from the initial voltages as noted by Nelson. I'm using the Fairchild JFets

 

[Dennis Hui]

There are no source resistors on the jfets so there are running at Idss.

So the voltage drop across R34/R35 is just the Idss times the resistance.
So the current is 4.7V/510 ohm ~ 9.2mA
A lot of numbers are different because with 510R for R35/R34 your mosfets are
now on. (See T6-T7 and T8-T9 voltages).

But things like G-T6 and G-T8 shouldn't change since those are just the rail voltages.
G-T4 and G-T2 also shouldn't change.

Please check these, as well as your raw DC rail voltages.

 

[bajjisw]

And please post a picture of your power supply, especially input and output connections.

 

[Rodeodave]

Something's not right. G-T6 should be pretty much the full positive supply voltage of 28V.

We need to see pics of the PSU, including transformer wiring.

 

[Jim50hertz]

I'm using a bench PSU. This one.

Is this not useable for the task?

Voltages are the same upon checking Dennis

 

[Ben Mah]

That is a 0-30V or 15V-0-15V supply. You need 28V-0-28V.

 

[bajjisw]

One or two ? If two, how are they wired ?

 

[Dennis Hui]

It looks consistent with setting 28V and getting +/-14V.

I think it's now time to pull out the transformer, caps and the
real power supply.

 

[Jim50hertz]

OK, very noob mistake then!!! Oops.

I'm repurposing my Aleph J PSU, I've a new transformer. I build up the PSU and report back.

 

[Jim50hertz]

Caps are rated 35v, is this OK?