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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
whitestix OP
386 posts
 
Update:  I earlier stated that the F5 runs as hot as a tube amp with four KT88 tubes.  That assertion is clearly wrong.  While the F5 runs much warmer than class A/B amps I have had, it generates nowhere near the heat generated by a robust tube amp.  My HK Citation II toasted the self above that in which it resided, but with the F5, the upper shelf is unaffected.  In conclusion, the F5 runs much warmer than a class D or class A/B, but far cooler than a tube amp.  Whitestix
kdude66
1,198 posts
 
Whitestix,

Are you still liking the sound and can you tell us any particulars


Kenny.
kosst_amojan
2,095 posts
 
I'm currently a matter of hours away from finishing a 50wpc version of the F5 using the standard F5 topology, not the F5 Turbo. (32V rails.) I'm getting very excited to hear what it's like. It's the first amp I've ever built so I'm not rushing to finish it. I'll be finishing wiring the PS tonight and testing it and hopefully begin setting bias tomorrow night. 
As far as I know, Nelson personally built most of the First Watt amps himself until recently when construction was transferred to the Pass Labs facility. 
I chose the F5 because it's a very simple, straight forward circuit as opposed to being pure current gain or obtaining voltage gain though a transformer or any number of the "unique" designs Pass dreams up. It's going to be powering Focal 936's and I felt a "normal kind of amp" (Nelson's words) would be the best place to start. 
The bottom line on why I chose to build one is real simple: How else are you going to obtain a Pass-designed amp for under $1000? You pretty much can't! Some aren't well suited to very reactive loads, like the F4 and J2, but some, like the F5, can be built up to drive a 1 ohm loads all day very reliably. And have human lips ever uttered "That Pass amp sounds like crap!"? I don't think so!
whitestix OP
386 posts
 
I'll bet you are getting very eager to complete the project and fire it up in your system.  I wish I had auditioned a First Watt amp 5 or 6 amps earlier as I would have saved a lot of dough.  Let us know how your masterpiece sounds when it is up and running.  
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.
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