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FH9HVX - Budget Conscious 100w Class AB for Lean Times

FX11

Will be using Prasis CRC supplypcb has to be populated:)
 

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Founder of XSA-Labs
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Hey guys, this amp has SMT compensation caps as optional - they are in parallel with through hole equivalent on the other side (typically silver mica’s). But do not fear the SMT caps. They are ever easy to install: use iron to tin one pad first; install chip cap with tweezer and use tweezers to apply pressure on top of part while applying heat to end with pre-tinned pad until it melts and flows; then solder the other end; done.
 
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The FH9HVX sounds better in a low sensitivity speaker such as 10F/RS225 FAST (82.4dB at 2.83v). The sound of Alpha Nirvana being Class A has smoother midrange like vocals but I can’t say it is better than FH9HVX overall unless it’s really critical listening. If you play at louder levels, the FH9HVX may be more to your liking.

X,

Thinking over your statement above I wondered what might be the reason. I would appreciate it if you could find time to unpack these statements a bit. Any thoughts on the cause?

I’m have more experience in the world of tubes, and there some folks think the wave crossover region (between push and pull) is exaggerated by highly sensitive speakers, and consequently people with their 105 db at 2.83v corner horns prefer single ended low watt amps. Is this why FH9HVX sounds “better” on low sensitivity speakers, or at high volumes?
 
Founder of XSA-Labs
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Mostly, I am saying that if you have speakers that need 50w to sound “alive” then a 39w amp is not going to sound as good because it is operating near clippping. Within its operating range, the class A Alpha Nirvana with its dominant second harmonic and descending higher orders will sound better. The FH9HVX is barely working at 39w and far away from clipping (the dominant source of distortion). Both amps have quite low THD but I believe the FH9HVX is lower, however, it has a slightly higher third harmonic distortion than the second so may sound a bit brighter on leading edge percussion. Some people like that, it’s very subtle. If I only had the Alpha Nirvana, I would build 89dB and higher speakers to pair with it. If I have 82dB speakers, I would use the FH9HVX. What is true though, is that both amps are pleasing to hear and non fatiguing. Can listen to them endlessly all day all night. Hope that helps.

They are both great sounding amps - just different applications for speakers. If you have a 9W SET tube amp, I would use >95dB sensitive speakers. Etc.
 
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Thanks for your reply. Much appreciated.

I have both sets of PCBs (with parts and transformers) waiting to be built; this winter hopefully. So, I will be able to hear both amps on my 92 dB Elsinore loudspeakers. And compare (listen) to a variety of tube amps in my stable. I hope to hear differences and be able to characterize them.
 
Francois G,

Good luck with the build and look forward to your listening impressions.

As X has already pointed out the SMD components are optional - you can opt for the through silver mica capacitors also; so don't let that hold you back.

Have you got your chassis sorted out?
 
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Zman01,

Thanks for your comments and encouragement. I think I do have my chassis sorted out! My Alpha Nirvana will have 12x12 inch heatsinks for sides (I bought these hunks years ago) and finished hardwood front & back (width to suite and with any additional heatsinks and connections). Top would be perforated stainless steel with Noctua fan sucking down (when necessary, controlled by temp) from the bottom. It would be a cube-like stereo amp, probably close to 12x12x12 inches. Sounds OK :grouphug:?

FH9 is easier, but similar 12” height heatsink (6” wide) sides and hardwood rest to suite.
 
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What preamps are people using with the FH9-HVX? Looking for what would be suitable/needed inbetween a DAC w/ line-level output. I'm seeing the Mezmerize B1 Buffer but believe that would be overkill as I only need a passive preamp w/ 2+ input selector w/ volume control. At the simplest sense I'm aware this is a pot w/ relays, but didn't know if this amp would benefit w/ a full attenuation design preamp.