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Sony Vfet Illustrated build guide
Sony Vfet Illustrated build guide
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Old 19th May 2020, 01:28 PM   #1061
Jim50hertz is offline Jim50hertz  United Kingdom
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Old 19th May 2020, 01:30 PM   #1062
Jim50hertz is offline Jim50hertz  United Kingdom
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Thanks Dennis. these are what I have. Fairchilds I think. Are there suggested alternative values for the resistors?
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Old 19th May 2020, 01:47 PM   #1063
Eric is offline Eric  United States
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Sony Vfet Illustrated build guide
That's a pretty nice PSU, Berny! With just a CRC, I measured 0.07 mV AC ripple on the speaker terminals. This is one VERY quiet amp!
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Old 19th May 2020, 04:02 PM   #1064
Dennis Hui is offline Dennis Hui  Canada
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Sony Vfet Illustrated build guide
Jim, there's a dependency on the Idss of the jfets. If your parts are at the upper
end of the B/BL grade range then may already be fine.

So for now assume you can't adjust the bias current sufficiently high.

Changing out P3 and P4 to 1K is probably the most 'universal' solution though
desoldering pots is a pain. An alternative is to change out the fixed resistors
R34/R35 which should be easier to desolder. You can measure the voltage
drops across R34/R35 to back out the jfet Idss. Once you have that info, you can
work out new R34/R35 values.
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Old 19th May 2020, 05:09 PM   #1065
Jim50hertz is offline Jim50hertz  United Kingdom
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Thanks Dennis. I’ve ordered some trimmers and will order some replacements for R34/35. I guess 500r? I’ll try getting the pots out first.

Question, do the Mosfets need matched? And is there any benefit to tracking down 2sk2013/2sj313? Other than avoiding desoldering parts and adjusting biasing approach.
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Old 19th May 2020, 08:38 PM   #1066
Dennis Hui is offline Dennis Hui  Canada
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Sony Vfet Illustrated build guide
Matching is not needed for proper operation though some may prefer to use NN and PP
pairs for the two channels. I think you got your kit from the diyaudio store and I
suggest sticking with the Fairchilds. (Lots of excellent builds with those already, plus
the Toshibas are hard to find.)

If you're ordering resistors, maybe both 500R and 750R and choose based on Idss
measurements?
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Old 20th May 2020, 10:55 AM   #1067
Jim50hertz is offline Jim50hertz  United Kingdom
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Thanks Dennis

Yes I got the kit from the DIY audio store, in the first round of kits.

I've ordered the resistors you suggest plus 1K trimmers.

Would you suggest replacing the trimmers AND R34/35?

Also is there a way to identify idss prior to installation in the circuit?

Last edited by Jim50hertz; 20th May 2020 at 11:11 AM.
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Old 20th May 2020, 11:08 AM   #1068
Dennis Hui is offline Dennis Hui  Canada
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Sony Vfet Illustrated build guide
If needed, I would suggest changing only one.
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Old 20th May 2020, 11:40 AM   #1069
Jim50hertz is offline Jim50hertz  United Kingdom
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Thanks Dennis will start with bumping the resistors to 510r and see what happens
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Old 23rd May 2020, 09:51 AM   #1070
Jim50hertz is offline Jim50hertz  United Kingdom
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Just a triple check before I stuff JFets, BJTs and Mosfets, I'm working with the DIY Audio kit, first round.

Q1 - LSK170
Q2 - LSJ74
Q3 - ZTX 450
Q4 - ZTX550
Q5 - FQ3P20
Q6 - FQP3N30

Confirmation much appreciated! And also to check that legendinf on PCB matches the orientation for these?

Thanks!

Jim

Last edited by Jim50hertz; 23rd May 2020 at 10:01 AM.
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