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Sony VFET Amplifier Part 2
Sony VFET Amplifier Part 2
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Old 12th June 2017, 12:29 AM   #3061
dbis is offline dbis  United States
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Default DC voltage question

Hey guys,

Could be a silly question but I just want to make sure everything is OK before applying power to those precious vfets. I've gotten to the voltage check part of the build. I'm using the same chassis and Diyaudio store PSU(with bridge rectifiers) that I used for my F5. I just had to swap out the F5 18Vac transformer for the vfet 22Vac one, Antek AS-3222. When I checked voltages I got the following:

123Vac from outlet
23.3Vac on Antek secondaries
+31.5Vdc and -31.5Vdc unloaded after PSU.

Sorry if I'm being a bit too cautious. I'm assuming that 31.5Vdc will come down a bit once loaded but I just wanted to see what you guys thought before going any further.

Thank you
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Old 12th June 2017, 12:46 AM   #3062
Zen Mod is offline Zen Mod  Serbia
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Sony VFET Amplifier Part 2
Quote:
Originally Posted by rumina View Post
I finished my Pass Sony VFET amplifier. Big thanks to Nelson Pass and diyAudio store making this project possible. I love it, sounds great. Was fun and easy to build also thanks to this forum, the members and all the good info and tips, thanks :-).
definitely Fugly!

just keep that NTC well of bottom plate

also , I'm afraid that plastic of that connection block will melt with time

better find some ceramic ones
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Old 12th June 2017, 01:49 AM   #3063
wdecho is offline wdecho  United States
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Quote:
Originally Posted by dbis View Post
Hey guys,

Could be a silly question but I just want to make sure everything is OK before applying power to those precious vfets. I've gotten to the voltage check part of the build. I'm using the same chassis and Diyaudio store PSU(with bridge rectifiers) that I used for my F5. I just had to swap out the F5 18Vac transformer for the vfet 22Vac one, Antek AS-3222. When I checked voltages I got the following:

123Vac from outlet
23.3Vac on Antek secondaries
+31.5Vdc and -31.5Vdc unloaded after PSU.

Sorry if I'm being a bit too cautious. I'm assuming that 31.5Vdc will come down a bit once loaded but I just wanted to see what you guys thought before going any further.

Thank you
I had approximately the same readings. Proceed, the voltages will drop with load.
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Old 12th June 2017, 05:51 AM   #3064
rumina is offline rumina  Switzerland
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thanks everyone for your nice feedback. the only thing that was hard with this amp was the adjusments with these single turn potentiometer, they are extrem sensitve, a gently tap with the scredriver on top changes the value, would be better to use multi turn pots here.

@zen mod thanks for the tip, ntc position is fine and save but the idea with a ceramic block is good, thanks to nice headsink size (350*130, a tad bigger then a 300*150) temperature is moderate for a class a amp.

Last edited by rumina; 12th June 2017 at 05:59 AM.
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Old 12th June 2017, 05:54 AM   #3065
dbis is offline dbis  United States
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Reply to post #3063:

Thanks wdecho.

Last edited by dbis; 12th June 2017 at 05:58 AM. Reason: Forgot to quote
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Old 12th June 2017, 06:00 AM   #3066
Gyuri is offline Gyuri  Hungary
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Don't worry, multi turns isn't much better in this regard.
Even there are ones whose are prefer single turns.
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Old 12th June 2017, 06:31 AM   #3067
Rodeodave is offline Rodeodave  Austria
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Sony VFET Amplifier Part 2
Multi-turn pots are not better. We've had this discussion earlier: http://www.diyaudio.com/forums/pass-...t-2-a-177.html It's the same conductive element, so on top of inferior long term stability of a setting due to the complicated mechanical coupling of the wiper to the mechanism, you also get backlash (reverse clearance, Umkehrspiel). So, be glad you installed single turn pots
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Old 12th June 2017, 07:44 AM   #3068
Zen Mod is offline Zen Mod  Serbia
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Sony VFET Amplifier Part 2
well , years ago I decided not to worry about these issues - one turn vs. multiturn

as long there is no difference in track+wiper quality between them , there is no difference neither in functionality nor resistance changes in time

I've seen them in all sorts of pro gear ...... so (for me ) that bush beat me long ago .....and I just chose to use multiturns everywhere

I have some other fixations to cure
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Old 15th June 2017, 03:07 PM   #3069
nagini262 is offline nagini262  Viet Nam
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My Sony VFET P2 after 1h warm up with BeO insulator

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Old 24th June 2017, 08:00 PM   #3070
rumina is offline rumina  Switzerland
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and now i have twins any my brother has his own vfet baby.

second time biasing was easier, best tip was to first bring t6/t7 and t8/t9 up to 1.4v with p3/p4, offest t18 around +-100mv and warm it up, wait 10min.

readjust p3/p4 for offset t18 around +-100mv then bring r32 up to 80mv with p1/p2, output offset +-50mv. wait 15 min.

now adjusting all 4 pots p1/p2 - p3/4 in cycle up to 1.45v at t6/t7 and t8/t9 and r32 to 90mv (check first t18), againg offset around t18 +-75mv and output offset +-50mv. baby steps needed or it run away fast (even more with one turn pots). let it heat up then for at last 30 min.

after this time r32 was a little bit under 100mv. go for 1.5v at t6/t7 and t8/9 and r32 to 100mv, check offest's. readjust again in cycle all 4 pots for the target bias and offsets. now with baby baby steps :-). wait after every adjustment some seconds, you get the feeling when the circuit get into a stable state. dont touch the small heatsinks, the offest over t18 acts at once. i done the final fine adjustment via p1/p2.

at the end i had a bias of 101 mv, offest t18 floating around +-50mv at t18 (1.51v) and output offsets +- 20mv.

remember everything up to +-200 mv over t18 is ok and +-50mv output offset is ok, +-50mv over t18 and +-20mv output offset is perfect for me. the amp needs 1 hour to get stable. floating around a bit is normal.

this way was a lot easier then put t6/t7 and t8/t9 direct to 1.5v, hope that helps.

don't rush :-).
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