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Jeff Rowlands Amp and Dac vs. VAC amp and DAC

Hello, I am new to this forum but I have a question. I am trying to pair an amp + DAC with my Wilson Sabrinas. I have listened to Jeff Rowlands integrated with the Aeris DAC. And the VAC Sigma integrated with the Aeris DAC. Price is a factor and so is space. Does the 625 need a pre-amp? Any suggestions or thoughts? 
rinpoche
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almarg
9,670 posts
 
Charles1dad 5-25-2016
Based on what Al has written it seems that the ARC tube amplifiers may utilize a larger degree of negative feedback (NFB) than the VAC amplifiers. I say this due to the lower output impedance (higher damping factor ) of the ARCs. Depending on the particular speakers this can be advantageous. It truly is dependent on the speaker design and intent of the builder. The Sabrinas could require amplifiers with more NFB with the resultant lower output impedance. Again, nothing substitutes for actual listening experiences.
Yes, that’s all true and well said, Charles. The VAC 200iq is specified as using 6 db of feedback, while the ARC Ref 150SE, for example, is specified as using 14 db, a considerable difference. I’ve never seen the corresponding number for the MC-275, but its unusually high damping factor (for a tube amp), its somewhat low gain (feedback reduces gain, everything else being equal), and numbers I’ve seen for other classic MC tube amps, suggest to me that it could be in the vicinity of 20 db or so.

My older VAC Renaissance 70/70 MkIII amplifier, btw, has a six-position switch that allows the user to select the amount of feedback. The settings range from zero to 7.5 db. I use the zero feedback position, which works well with my particular speakers (which have a particularly flat impedance curve and no dips to low values at any frequency).

As you indicated, judicious use of feedback in a design can be either advantageous or disadvantageous depending on the characteristics of the speaker that is being driven. And also on how well the design of the particular amp avoids the sonic downsides that feedback can potentially introduce.

Best regards,
-- Al


rinpoche OP
154 posts
 
So far, it sounds like JR is still winning for combining great sound and ease of use. And perhaps the VAC 200iq is next given its new self-biasing feature, though I have still to hear it. The exciting listening adventure continues!! 
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mapman
22,475 posts
 

ARC seems to know how to do NF with tube amps right and on paper would seem to be called for with the Wilson speakers.


I lost track. Is ARC versus VAC versus JR in home with the Wilsons the shootout? Or just JR versus VAC?

Its a great shootout by the way. Three of my absolute favorite brands each with unique pros and cons. Any tickets available? :^)

  Can't wait to hear the results.
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charles1dad
10,250 posts
 
Mapman,
I don’t believe that ARC gets the use of NFB anymore (or less ) right than does VAC. I say this because it strictly depends on the speaker in question. For example Al’s speaker sounds better with his amplifier’s zero NFB setting . In fact the scenario is true in my case as well. My particular speakers sound their very best with my zero NFB amplifier compared to those with NFB.

So again depending on the speaker characteristics either the ARC or the VAC could be the "ideal" choice. ARC’s 14 db of NFB may or may not be the preferred amount. Amplifiers which offer selectable NFB levels are  a very good approach as it provides flexibility. Perhaps the Sabrinas are more compatible with amplifiers that rely on increased NFB.
Charles,
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mapman
22,475 posts
 

Charles I simply meant they get it right for their products as designed not that they do it any better or worse than others who do it differently for different reasons. Practically their tube amp market share probably does help confirm the relative effectiveness of their approach for many using many different speaker designs.


I would love to own a VAC but would probably only do it if I were willing to build my system around it, mainly the speakers. Atmasphere (OTL) is another example of a higher output impedance tube amp that dictates certain speakers more for best results. SET tube amps are of course another.  


ARC tube amps would seem to fit better for more that build around certain speakers that may be a harder load to drive but still prefer a tube amp.

Different strokes......

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