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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
1,200 posts
 
Yes speaker matching with first watt amps is very important,
going to be interesting to see the upcoming new ones that Nelson is working on.

I've heard through the Diy community that he is working on a F8 and also a Sit3.

Also pass labs has the Xa-25 out,but I haven't heard that one yet,
might be a good option for lesser effficent speakers.


Kenny.
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whitestix OP
720 posts
 
Kosst,
Great information!  You clearly know your way around electronics. I am going to attend Burning Amp this fall down the road in San Francisco to meet "Papa" again.  It is funny that you mention the KEF LS50's.  I bought them shortly after they came out and drove them with a 175 wpc Plinius 8200 MK II integrated amp and the amp rather struggled to drive them properly. There is no chance a FW amp would be compatible with them.

However, with OB speakers like my Spatial Audio Holograms, DeVores, Omegas, etc, the FW amps are a great match it seems to me.  Forget about Martin Logans and the like, but a pair of Klipsch speakers would sign with these amps.  You and Kenny wisely pointed out in your posts the compatibility issues one needs to be aware of to get the the best performance from the FW variants.  

 



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kalali's avatar
kalali
1,977 posts
 
My very simpleminded/layman observation is some amps put out more power as the load is reduced which implies a near constant voltage delivery. Others behave the opposite which seems to imply a constant current source. The former is better for low impedance loads whereas the latter better for higher impedance speakers.This is also evident when comparing solid state and tube designs. I know I’m stating what most folks already know but a good layman view of the amplifier differences and how to find matching speakers.
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