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Full blown Kal Rubinson review and in depth JA measurements....

Posted by AbeCollins on December 6, 2024 at 13:20:11:
In the Stereophile January 2025 issue the review article begins on page 77. It is 5 pages long including measurements by JA and a sidebar by Paul Miller on Class D evolution. I read the entire review (rare for me!) but I skimmed over the music that Kal used as I am unfamiliar with it. That's completely on me and others might find it useful.
Buckeye PURIFI EIGENTAKT 1ET9040BA1 monoblocks
$2300/pair sold direct includes free shipping in USA
My take under the heading of Inevitable comparisons:
Kal could hardly discern the sonic differences between the Buckeye PURIFI 1ET9040BA1 monoblocks, NAD M23 Master Series PURIFI stereo amp, and his reference two Benchmark AHB2 stereo amps each bridged for monoblock duty.
He mentioned noticing slight differences in bass or treble between the amps upon A/B switching but those impressions were short lived writing, "However, within minutes, none of those impressions remained apparent; only the characteristics of the music and recording mattered, and I never felt the need to change from one amp to another." Kal still prefers his AHB2 "due mostly to matters of ergonomics and familiarity." Kal did mention that the XLR connector on the Buckeye is not a locking XLR so your XLR cable might slip out if you move the amp around. He suggests powering it OFF before moving the amp.
On the tech side:
I read that the Purifi modules require an input board with gain and Buckeye has their own design but there was no detail on it in the articl. VTV on the other hand makes their own input board that allows the buyer to choose from a variety of op-amps and discrete op-amps.... for a price. Buckeye includes a 12v trigger input. VTV offers it.... for a price.
Worth noting from John Atkinson:
The voltage gain at 1kHz into 8 Ohms was very close to the specified figures, at 25.6dB (High), 20.5dB (Med), and 15.5dB (Low).
Buckeye specs the monoblock input impedance as 51K Ohms. JA measured 8.4K Ohms regardless of gain setting. Why the big discrepancy? I have no idea.
[Edit] I think I found the discrepancy. 51k Ohm is the input impedance of the Purifi modules. According to the Buckeye website their custom input board uses a TI TI OPA1656 OP Amp and I'm guessing that the design around this TI Op Amp resulted in an input impedance of 8.4K Ohm as measured by JA.