Best Tube Amp For Sonus Faber? Or Pass XA-100.5? $6-7,500 Budget, Purchasing Used.

The 8ohm taps were clearly better, and had a hard time understanding why based on the impedance graph.   There is another audiogon forum discussing this where someone else mentions the Olympica III runs better on 8ohm taps for them too.   It was interesting, because the Primaluna taps were, 4, 8, 16.    But the VAC 200 iQ (and probably other VACs) have ranges for their ohm taps:  1-2, 2-4, 4-8.   This may explain better why the VAC runs the Sonus Fabers better, since there is a broad range where the ohms are constantly changing.  Maybe the VAC is better at handling this?   Not sure.   All I know if the 4-8 ohm taps (and the 8 on the Primaluna) were clearly better.   Judge by your ears in the final analysis.

Nightfall, the Preamp I have been saving for.  Initially was the Primaluna preamp, but would eventually love to upgrade to one of the following (again a tube guy):  Zesto Leto, EAR Yoshino 868 or 912, Herron Audio, or VAC.   I think VAC is coming out with a more affordable preamp this year.... at least that was the rumor a while ago.  

georgehifi,

I noticed the bass improvement the most when going from the primaluna to the VAC.  that would coincide with what you were saying.  The best bass on a tube amp I've heard was with the VAC.

Nightfall,

Remember that the Olympica III is moderately efficient at 90+db.  so even if it dips low with the ohms briefly, there is more at play with how well an amp can drive speakers.  The VAC dealer on the audio shark forum commented that the 100 watt specs for the 200 iQ was very conservative, and is likely much more power that is giving out.  I've noticed that in my experience with it as well.

djfst,

My current preamplifier is the top of the line PrimaLuna Dialogue Premium, which I have loaded up with very good NOS tubes. I find it to be a giant killer under $10k (granted I stole that line from Kevin Deal who may be  a bit biased, but the reviews support it). 

My list of dream preamps would include the Joule Electra LA-300ME and LA-150-SE, the Conrad Johnson ART 2, the Zesto, and something from VAC. 

I've read great things about the Herron, but have never auditioned one or otherwise had experience with that preamp. What can you tell me about it?

You may be right about the Primaluna - I haven't used NOS tubes yet, so it may be all you need with whatever reference amp you end up with.  I've told by many that the the preamp selection will influence the sound a lot...  The Herron was recommended to me numerous times by a trusted dealer who I value his opinion.  He has never steered me wrong in the past.  Unfortunately, his store is a plane ride away and haven't been able to demo it yet.   I also tend to like to buy things made in the USA - to support local manufacturers and in case of a problem with the unit down the road, they are a simple phone call away.   That can't be underestimated, especially when you are talking about shipping a 100+ amp around the country vs across the world.  VAC, Zesto, Herron, VPI, etc.  are all companies I'd be happy to own and support.   Sonus Faber was the exception :)