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DIY Pass Labs First Watt F5 amp impressions

I recently acquired a well- built DIY First Watt F5 amp for the cost of the parts, which is the understanding among those that build the designs that Nelson Pass has made available to the DIY folks.  I have been using a McCormack DNA .05 Deluxe amp and a Don Sachs 6NS7 tube amp to drive my Spatial Audio M4S Turbo S Hologram open-baffle speakers, which are ~94 db efficient.  I have raved about the McCormack amp on this forum, but swapping the F5 for the McCormack amp has been a  sheer revelation.  I have had dozens of tube and class A/B amps my system over the past 4 decades, as well as a couple of very good class D amps recently, but the tonal accuracy and 3-D representation of music with this F5 is simply stunning.  It is offers a glimpse into the inner details of the music.  I do not have the superlatives to describe the musical enjoyment of the addition  this amp provides to my system.  I am put off the heat his amp generates -- similar to that with a tube amp with a quad of KT88's, but it is a fair bargain for the most ruthlessly revealing sound reproduction I have ever heard in my system.  My regret is that I waited so long to have a Nelson Pass-designed amp in my system.  If your speakers are quite efficient, there are several variants in the First Watt line of amps that might be a great match for your system.  Mark at Reno Audio is the guy to help you sort out the best amp for your needs.
Cheers, Mark
whitestix
kdude66
1,198 posts
 
Very nice and fun to build your own amp,
I built both the F5 and the turbo version from the kits from the diy store but I wasn't quick enough to buy the nos Sony Vfet's that were available as matched pairs to build the push pull version of the stereo sit.

I wish you the best in sound,

Kenny.
kosst_amojan
2,095 posts
 
I got my boards, transistors, and case through the diyaudiostore too. Real good stuff. I'm definitely getting excited to hear it. I think my next project is going to be a B1 buffer pre-amp. Need to dig into that world a bit and learn more though. I'll be back to let you know how it sounds, assuming I don't accidentally reduce it to smoldering rubble. Pretty nervous about that first power up moment. 
kdude66
1,198 posts
 
I can relate to you being nervous I was as well.

I work at a major airline as a Avionics technician for 29 yrs now and I work on some pretty complex stuff but It's not like the satisfaction I get when I build a Amp or do mods to my gear.

My best advice is triple check every little detail of the build including every solder joint.Be sure and be careful and take your time when it comes time to set the proper bias,allow proper warm up time and stabilization periods and make small adjustments until you reach the proper bias and remeasure after a period of time.Make sure you have very minimal DC at the outputs.

If you have any issue those experienced guys on the pass labs portion on the diy site can definitely help you.

Also the amp will need about 200 hrs of breakin time,mainly for the capacitors to sound It's best.

Kenny.
kosst_amojan
2,095 posts
 
The bias is going to have to be something I play by ear on account of the 32V rails. I've got a sheet of copper and I'm debating bolting some sinking made of that to the top sides of the MOSFETs. Last night I learned that the power supply works a lot better with fuses installed in the power input module. Don't know why I just assumed there was one in there. It made me double check a bunch of stuff though! Hopefully tomorrow night it'll be done. We'll see. 
kosst_amojan
2,095 posts
 
I'm listening to the amp as a write this and it sounds incredible! Very visceral, physical, deep, and richly textured sound indeed! It still needs a bunch of time burning in and to have the bias adjusted up a bit more, but I love the thing already. 
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