@andios
I’m pretty certain that you meant "sin(x)/x," short for "sine(x)/x." Which of course has nothing to do with sinuses :-)
I’m also pretty certain that research of published measurements of various non-oversampling DACs will show insignificant rolloff at 20 kHz.
Regards,
-- Al
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I agree with Charles' comment as well. I would add that the knowledge and experience that goes into the design of the printed circuit board itself can make a big difference in the performance of a DAC. How signals, power, and grounds are routed and distributed within the circuit board, and also how power is "decoupled" (i.e., filtered) immediately adjacent to all of the critical chips, are all hugely important in a DAC design.
Best regards,
-- Al
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To add to the foregoing comments, it’s worth noting that the DAC uses eight of the TDA1543 d/a converter chips (each of which can handle two channels), in "a complex parallel configuration." And eight chips are used even though the DAC only provides single-ended outputs, with just one output signal having to be generated for each of the two channels. Assuming good design, that will result in considerably better performance than if only one chip was used.
Regards,
-- Al |
@Snopro
Thanks for your comment, Joe. I had considered the possibility of waiting for the SIT-3, but I decided that it wouldn’t be suitable for my purposes.
One reason being its VERY low gain (spec’d at 11.5 db), which would make it a non-starter for my system.
Another being that its power capability (spec’d at 18 watts and 30 watts for 8 ohms and 4 ohms respectively) is probably marginal (or worse) with my speakers, when listening to the many classical symphonic recordings that are in my collection that have been engineered with minimal or no dynamic compression, on labels such as Telarc, Reference Recordings, Sheffield Labs, Chesky, etc. In fact I might not have purchased the XA25 were it not for John Atkinson’s measurements which indicated a maximum power capability (presumably after leaving class A) of 80 watts and 130 watts into 8 and 4 ohms respectively. (My speakers are spec’d at 97.5 db, with a nominal impedance of 6 ohms, and are said to be close to that impedance throughout almost all of the frequency range).
Best regards,
-- Al
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@d2girls, thanks for the tip!
The manual for the XA25 states that it takes about an hour to fully warm up, and that coincides with the amount of time I have observed it to take to reach a stable temperature on its heat sinks. So rather than leaving it on 24/7 my usual practice is to simply turn it on about an hour or so before I do any critical listening.
For break-in purposes, Mark at Reno Hi-Fi had suggested leaving it on 24/7 for 5 days to fully break it in. But out of an abundance of caution, especially given that it is a brand new amp, I left it on for most of the 24 hours of each of day, until it reached 120 hours, but not while asleep or when no one was home.
Thanks again. Best regards,
-- Al
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@Charles1dad
Thanks, Charles. I suspect that I’ll eventually sell the VAC, but I won’t decide until sometime after I receive it back. The XA25 is definitely a keeper, though, for the long term. It comes amazingly close to the VAC with respect to dimensionality, imaging, liquidity, and other traditional fortes of high quality tube amps. It’s a bit less rich sounding than the VAC, but I interpret that as an increase in accuracy, which is fine as far as I am concerned.
There are also some non-sonic factors favoring the XA25, including the likelihood of greater reliability in the years ahead considering the age of the VAC; the fact that even though both amps operate in class A the XA25 puts only 240 watts of heat into the room compared to what I believe is upwards of 700 watts for the VAC; and the cost that would be involved in re-tubing eight 300Bs if and when that were to become necessary.
This is the first time I’ve had a high quality solid state amp in my system in about 25 years, and I believe I’ve picked the right time and the right model with which to do so again. Thanks in part to Terry's review.
Best regards,
-- Al
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Regarding Teajay's credibility as a reviewer, I can add a data point based on actual recent experience. I very recently purchased a Pass XA25 amplifier (from Mark at Reno Hi-Fi, who of course was completely wonderful to deal with), motivated in part by the glowing reviews and comments it has received from Terry and many others, and in part by the fact that my VAC Renaissance 70/70 amplifier developed a problem and is back at the factory for repair. Although I've had the XA25 for just a bit more than a week I can say that in my system, at least, the detailed characterization of its sonics Terry provided in his review were absolutely spot on in every respect. And in fact were more focused, meaningful, and accurate, IMO, than the comments in the comparably glowing review Herb Reichert provided in Stereophile.
Thanks for your excellent review, Terry; I expect to enjoy this amplifier for many years!
Regards,
-- Al
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