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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
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. 
whitestix OP
386 posts
 
Let me be the first to say that I am very happy to hear you are enjoying the sound of your First Watt amp build!  I have had a ton of amps in the past 45 or so years and the F5, with a pair of compatible speakers, is  a sheer glimpse of audio nirvana.  I will say that my F5 does have a bit of a bright edge to the leading notes of music --- no amp is perfect of course, but it reveals music in my recordings with a visceral impact that I have formerly not heard.  I reckon after a couple hundred hours of burn-in with your amp, you will be even happier.  Cheers, Whitestix
kosst_amojan
2,095 posts
 
Thank you very much! It does have a brightness to it, but it almost seems like it’s just that much more clear and detailed up high than I’m used to which may be why it sticks out. There aren’t any negative characteristics of the highs except that they’re just there. To be expected of an amp with the specified bandwidth of DC-1,000,000Hz and nothing limiting it I suppose. There’s greater crimes an amp could commit! I’m extremely pleased with it all around! I’ve never heard an amp with this kind of imaging, punch, clarity, speed and delicacy before. It really is like a revelation. It’s definitely going to be a benchmark I judge all other amps by. I’m driving a pair of Focal Aria 936’s with it and it grips them with surreal authority. It seems an excellent pairing given their complementary strengths. I’m truly thrilled to have a rig like this in my living room. It’s a privilege and an honor to be able to hear music like this. I’m also tickled that Nelson Pass called me a "fearless amp builder" for going with 32V rails and yanking out all the current limiting.
kdude66
1,198 posts
 
Very nicely done I hope you enjoy the tunes of your labor,
Quite a bit of satisfaction in building and or modifying your own gear.

Kenny.
kosst_amojan
2,095 posts
 
I'm totally loving the thing. The thing runs blazing hot. I'm running about 2.2 amp of bias through it and it idles at 55C on the sinks and about 77.5C on the MOSFETs. Maybe I could eek more out of it, but 2.2 amp of bias on rails that actually measure 34.5V is already pretty bold. Anything more would be diminishing returns. I'm pretty sure I'm a full convert to class A and Nelson Pass designs. 
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