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
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 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
I had approximately the same readings. Proceed, the voltages will drop with load.
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.
@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.
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Multi-turn pots are not better. We've had this discussion earlier: http://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-part-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
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
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
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.
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
.Attachments
i know i wake up a little late
please give me a sign
You may be in luck:
http://www.diyaudio.com/forums/pass-labs/307071-what-do-those-2sj28s-21.html#post5108495
great as i still have a pair of 2SK82 somewhere , thanks
Not just what to do with your existing parts, but Papa mentioned a small 4th round. Better sign up quick when the time comes.
Cheers,
Dennis
Know DF numbers is show on this photo corner.
45 that ready relatively high damping factor.
Usual First Watt DF values exception F7 is around 20 or less.
You build F7 version with the vfet's
or make Diy Sony Vfet amp with F7 Mr Pass "PCF touch"
haha only expert's knows right answer me not
45 that ready relatively high damping factor.
Usual First Watt DF values exception F7 is around 20 or less.
You build F7 version with the vfet's
or make Diy Sony Vfet amp with F7 Mr Pass "PCF touch"
haha only expert's knows right answer me not
Attachments
Its up! Thanks Nelson for a great amp! I prefer this to the F6 - I don't exactly know how to describe the difference, but it sounds more 'whole' and more detailed. Contradiction?
Used the kit, with Toshibas replacing the Linear System Jfets and the Fairchild mosfets.
Sent from my iPad using Tapatalk
Used the kit, with Toshibas replacing the Linear System Jfets and the Fairchild mosfets.
Sent from my iPad using Tapatalk