Building my first Pass amplifier - the F6. The last amp I build was a UCD than 10 years ago. Build is still in progress - I have just finished testing the F6 boards using a bench power supply. Manage to get it to bias around 600mV - still creeping up slowly as the temperature increases. I will need to fine tune it once i put them into a case. Power supply parts are still on the way, so, I have to wait
Photos attached - this is the 'simple' ac degeneration version. Boards from diyaudiostore, with SK170/SJ74/IRFP240.
Nice! Probably one of the better choices from Pass' stable in sunny ☀️ Singapore
Best,
Anand.
Nice! Probably one of the better choices from Pass' stable in sunny ☀️ Singapore
Best,
Anand.
Just a bit worried about the temperature. Out of the chassis, the heatsink is already hitting 55 degrees C. I may have to dial down the bias when I put it into the chassis. This is the Tropics!!!!
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"Don't Panic!"
We have had some discussion recently and the thought was that an F6 sounds better at lower bias.
"Don't Panic!"
We have had some discussion recently and the thought was that an F6 sounds better at lower bias.
Thanks
. I am already at the typical FirstWatt bias current. Will look into this again once i finish my power supply.Is this with your heatsinks down on the table? If so stand them up with the mosfets on the lower half.
Yes. headsinks down on table. Standing them upright will improve ventilation. Hopefully this will balance off the impact of a closed chassis.
Trythe zenner mod which I believe makes the amp more stable.
If creating an order consider using
LM329DZ. 6.9V As Zenners with
R7, R8 3k3 resistors.
Read through the build guide for the theory.
Just finished up my first amp build (F6) ... absolutely thrilled with it! I followed 6L6 pretty much verbatim. I did use 6.8v for Z1/Z2 and switch R7/R8 3.3K as spelled out by ZenMod. Takes it better part of an hour, but bias is very stable at 510mV right now ... will probably leave it there for a while (maybe forever) as it sounds fantastic and is running around 51C.
As others are mentioning, finding the JFETs is quite a challenge at this time. Reading through other threads I saw alot of people have used Spencer Cheung (skcheung68@hotmail.com) for sourcing. He's asking about $46 (US) for two matched sets, so I figured I'd try it. They seems to be authentic pieces and are matched nicely ... plus the amp sounds great, so I'm happy.
Thanks to everyone for this thread (and forum), I couldn't have done it without you all. Think I'll try a Pearl 2 next and then maybe a F3 pre-amp ... I'm hooked!
As others are mentioning, finding the JFETs is quite a challenge at this time. Reading through other threads I saw alot of people have used Spencer Cheung (skcheung68@hotmail.com) for sourcing. He's asking about $46 (US) for two matched sets, so I figured I'd try it. They seems to be authentic pieces and are matched nicely ... plus the amp sounds great, so I'm happy.
Thanks to everyone for this thread (and forum), I couldn't have done it without you all. Think I'll try a Pearl 2 next and then maybe a F3 pre-amp ... I'm hooked!
