Jeff Rowlands Amp and Dac vs. VAC amp and DAC

I have listened to Jeff Rowlands integrated with the Aeris DAC. And the VAC Sigma integrated with the Aeris DAC....  I have heard the VAC Sigma 160iSE and the JR 625 upgrade both with the Aeris as the DAC.

Am I correct in inferring that you have not heard either amp with the Wilson Sabrinas?

While I am a big VAC fan, I would have some concern about how well suited the Sigma integrated (and many other tube amps, especially those which use minimal amounts of feedback) may be for use with that particular speaker.  Per John Atkinson's measurements:

My estimate of the Sabrina's voltage sensitivity on the tweeter axis was 88.2dB/2.83V/m, slightly higher than the specified 87dB. Wilson specifies the Sabrina's electrical impedance as 4 ohms, with a minimum magnitude of 2.53 ohms at 139Hz. My measurement of the impedance is shown in fig.1: the value (solid trace) varies between 4 and 6 ohms between 250Hz and 4kHz, and the minimum magnitude is 2.44 ohms at 135Hz. However, there is also a combination of 4.44 ohms and a capacitive phase angle of –58° at 72Hz, a frequency where music can have considerable energy; this will place a significant demand for current on the partnering amplifier.

Although the output impedance of the VAC integrated is not specified, I suspect that it is not particularly low, because I would expect a VAC design to avoid heavy-handed application of feedback.  Given the speaker's impedance variation from about 2.4 ohms in important parts of the bass region to substantially higher values at higher frequencies, especially in the treble region (as shown in Figure 1 of JA's measurements), the result of that combination is likely to be some degree of weakness in the bass, and some degree of over-emphasis of part or all of the treble region.

Also, given the speaker's 4 ohm nominal impedance be aware that the measured sensitivity of 88.2db/2.83V/1m corresponds to only 85.2db/1 watt/1 meter.  Which suggests that 86 watts of amplification may not be enough, especially if your listening includes material having wide dynamic range, such as well recorded minimally compressed classical symphonic music. 

Good luck, however you decide to proceed.  Regards,
-- Al
 

Thank you. I appreciate the detailed information. It is well beyond my comprehension, but I do understand your bottom line advice. I have not heard either amps with the Wilson speakers. I would have to take them to the store and I don't really think I can manage that. The store does not seem open to letting me bring the amps home. I listened on bigger Focal speakers -- and more expensive Focal speakers. They both sounded very good, but tubes (as I am realizing) have a little magic that SS doesn't. But, the JR was really good as well. The owner of the store thinks it should be fine with the Wilson's. I emailed the Wilson people and they also like VAC, VTL, and ARC with the Sabrinas. Thing is, everything costs so much (to my mind) and I want to get it right. Your help is part of the process and it is appreciated. 

By the way, do you have suggestions for other amp pairings with the Wilson Sabrinas? I am open-minded at this point. 

rinpoche for a purchase of this magnitude any good store should let you do an in-home audtion, I assume the store is local to you? Perhaps the owner can bring the amps over and at least do an audition with your speakers if he won't lend you an amp? I would expect better service than what you're describing for a good brick and mortar shop.

Thank you -- I will ask if they will do it. When I asked one of the guys in the shop he said, 'bring in your speakers'. They have been around a long time so I will see if they are willing to do it. It is one DAC and 2 amps. Should be worth it for a purchase of this magnitude, as you rightly say. That is a great suggestion. Thanks.