Sony Vfet Illustrated build guide - Page 43

Ben Mah · 9th January 2018, 01:47 AM

Another beneficial addition are transformer snubbers between transformer secondaries and diode bridges. See "simple no-math transformer snubber using Quasimodo test jig" in the Power Supply forum for information.

flocchini · 9th January 2018, 03:46 PM

Can the Sony VFet front end be used as a linestage/preamp as has been done with the BA3?

Thanks

Bob

6L6 · 9th January 2018, 03:59 PM

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.

flocchini · 9th January 2018, 04:49 PM

Thanks Jim

Msr Mojo · 10th January 2018, 06:21 PM

Did I miss something?
Were the VFET part 2 P1 and P2 pots changed from 5Kohm to 500 ohm for the supplemental kits?
I got (4) 500 ohm pots, (no 5Kohm units) in each supplemental kit.
Is there a post I can refer to?
Thanks.

wdecho · 10th January 2018, 07:33 PM

The build requires (4) 500 ohm and (4) 5K ohms pots. If you use Fairchild mosfets you need to change the 500 ohm pots for 1K pots to be able to bias properly.

Arye · 12th January 2018, 08:15 AM

Hi to all
There's a good bargain for screw terminal caps on Ebay (18000uf 80v 85c).
Will you recommend it for the PSU?

delecoy · 01:50 AM

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?

PJN · 17th January 2018, 01:51 AM

Not only will it make your cheap speakers sound good, it will make your fancy ones sound great.

delecoy · 17th January 2018, 03:28 AM

Mmmmmhmmmmm. That it does.

9th January 2018, 03:46 PM	#422
flocchini diyAudio Member Join Date: Feb 2004 Location: Davis,CA	FE as linestage Can the Sony VFet front end be used as a linestage/preamp as has been done with the BA3? Thanks Bob

9th January 2018, 03:59 PM	#423
6L6 diyAudio Moderator Join Date: Oct 2010 Location: Denver, Colorado	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. __________________ Illustrated Build Guides - Pass F4 - Pass B1 - Pass F5 - Pearl 2 - O2 HPA - Hagerman Bugle 2 - Pass Aleph J - Me at BA '13 -Pass F5Turbo - BA-3 Amp - BA-3 Preamp - F6 AmpCampAmp

10th January 2018, 06:21 PM	#425
Msr Mojo diyAudio Member Join Date: Jul 2015	P1 and P2 pot values Did I miss something? Were the VFET part 2 P1 and P2 pots changed from 5Kohm to 500 ohm for the supplemental kits? I got (4) 500 ohm pots, (no 5Kohm units) in each supplemental kit. Is there a post I can refer to? Thanks.

12th January 2018, 08:15 AM	#427
Arye diyAudio Member Join Date: Jun 2003 Location: Mitzpeh Aviv	PSU caps Hi to all There's a good bargain for screw terminal caps on Ebay (18000uf 80v 85c). Will you recommend it for the PSU?

17th January 2018, 01:37 AM	#428
delecoy diyAudio Member Join Date: Nov 2011 Location: Austin, TX	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? Last edited by delecoy; 17th January 2018 at 01:50 AM. Reason: Clarity


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9th January 2018, 01:47 AM	#421
Ben Mah diyAudio Member Join Date: May 2012 Location: Vancouver	Another beneficial addition are transformer snubbers between transformer secondaries and diode bridges. See "simple no-math transformer snubber using Quasimodo test jig" in the Power Supply forum for information.

9th January 2018, 04:49 PM	#424
flocchini diyAudio Member Join Date: Feb 2004 Location: Davis,CA	Thanks Jim

10th January 2018, 07:33 PM	#426
wdecho diyAudio Member Join Date: Oct 2014	The build requires (4) 500 ohm and (4) 5K ohms pots. If you use Fairchild mosfets you need to change the 500 ohm pots for 1K pots to be able to bias properly.

17th January 2018, 01:51 AM	#429
PJN diyAudio Member Join Date: Dec 2004 Location: Pa, USA	Not only will it make your cheap speakers sound good, it will make your fancy ones sound great.

17th January 2018, 03:28 AM	#430
delecoy diyAudio Member Join Date: Nov 2011 Location: Austin, TX	Mmmmmhmmmmm. That it does.

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