The sleek, good-looking 350Mc monoblock sits in the middle of the FPB series. Specified power is 350Wpc into 8 ohms, 700 big ones into 4, and a whopping 1400W into punishing 2 ohm loads. 250W and 650W…
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With its latest series of FPB (Full Power Balanced) amplifiers, Krell is taking careful aim at the seam between classic high-power two-channel systems and quality multi-channel installations where sound is yet paramount. Nevertheless, Krell founder Dan D'Agostino was adamant: Krell's Class A components were designed for music playback. "I'm a purist, like you, Jonathan!" he told me.
Hand-in-hand, Motorola microprocessors control optimization of Krell's Sustained Plateau Bias II system. The updated circuitry "evaluates" both the musical signal and the speaker impedance and passes that information along to the microprocessors charged with dynamically adjusting the bias plateaus to keep the amp in class-A "during any musical passage or speaker condition." Each bias plateau is sustained from 30 to 90 seconds, so the output stage is always ready to rumble. "Jonathan," Dan enthused, "it's simple. Class-A is the most linear, lowest distortion mode of operation—full current for…
"CAST has another important aspect. It really doesn't matter how long the connecting cable is because the cable's reactive effects are still never going to be more than a negligible part of the total circuit impedance. This means that preamplifiers and power amplifiers can be placed where needed, unconstrained by cabling problems."
Well hey now, that sounds like the ideal solution! So I spent a fair amount of time playing the KCT two-zone preamplifier and KPS28c CD player into the 350Mcs using both CAST and "standard" interconnects. Here's where I come down on the matter: CAST technology…
Just so our world-music readers don't think I've given up the Trip Hop ghost, I'll turn now to "Shining" on Peter Kruder's Peace Orchestra (G-CD 004) Notes: "That voice, she's so focused, luminous, round and real, it's just fantastic! The Krells lay her out stunningly. Contact! Plaintive, poignant, sweet and ambient, just plain killer. Aural candy, but not at all euphonically flawed." The low bass was deeply resonant, the powerful fundamentals filleting out the bottom end. The very top was, it has to be said, just a tad hashy, but not too bad. Considering that those highs are in the…
Sidebar 1: Specifications
Description: Solid-state monoblock power amplifier with "Sustained Bias Plateau II," class-A output stage and optional remote control. Inputs: one balanced (XLR), one Krell CAST (4-pin bayonet). Loudspeaker outputs: two pairs. Output power: 350W into 8 ohms (25.4dBW), 700W into 4 ohms (25.4dBW), 1400W into 2 ohms (25.4dBW). Output voltage: 60V RMS (170V peak-peak). Voltage gain: 26.4dB. Frequency response: 20Hz-20kHz, +0dB, -0.05dB; 0.1Hz-240kHz, +0db, -3dB. S/N Ratio: 118dB (A-weighted, no reference level given)). THD (balanced drive, unweighted): less than 0.…
Sidebar 2: Associated components
Digital Playback: Accuphase DP-75V 192/24 upsampling CD player, dCS 972 digital-digital converter and dCS Elgar D/A processor running at 24/192, Marantz SA-1 SACD player.
Preamplifiers: Mark Levinson No.32 Reference, Krell KCT.
Power Amplifiers: Linn Klimax Solo 500s, Forsell Statement.
Loudspeakers: JMLab Utopias.
Interconnect: Krell CAST, Synergistic Designers Reference Active Shielding, Cardas Golden Reference, Linn Silver.
Loudspeaker Cables: Synergistic Designers Reference, Tara The One, Audioquest Everest, Cardas Golden Cross, XLO The…
Sidebar 3: Measurements
Of necessity, all the measurements on the FPB 350mc were performed using its conventional, voltage-drive balanced input. The voltage gain into 8 ohms was 26.3dB and the amplifier didn't invert signal polarity (pin 2 of the XLR wired as "hot"). The input impedance was usefully higher than specified, at 187k ohms, while the output impedance was 0.18 ohms at 1kHz and 20kHz, 0.15 ohms at 20Hz. This is a little higher than we usually find with solid-state designs, indicating low overall negative feedback, and resulted in ±0.1dB of response modification with our…
Fig.4 reveals that at low levels, this distortion is primarily third-harmonic. (The amplitude of the lower trace in this graph is very much exaggerated for clarity; its absolute level was below 0.005%.) At very high levels (fig.5), the third harmonic is joined by a regularly decreasing series of higher odd harmonics, though these are all at or below -80dB! Intermodulation distortion (fig.6) was also low, even at very high power levels—this graph was taken just below the visible clipping point into 4 ohms.
Fig.4 Krell FPB 350mc, 1kHz waveform at 53W into 8 ohms (top), distortion…
I don't know whether Sam Tellig or I first discovered the delights of some slightly idiosyncratic loudspeakers made by Triangle—Tree-ON-gle, if you add the relevant accent—in the northeastern corner of France. I do recall feeling quite relieved to find that I wasn't the only hi-fi writer who liked and wrote about them.
My audio journey began with a pair of the very earliest Spendor BC1s, and my tastes evolved within a framework established by the icons of UK loudspeaker design. British speaker companies have been so strong internationally that relatively few foreign brands attempted to…
Most unusual of all is the tweeter, which adds considerable and substantial horn loading to a 1" titanium dome. Though it's not a view I share, horns have long been regarded with deep suspicion by large sections of the hi-fi fraternity, so I asked Triangle why they'd opted for this unconventional solution. Their surprising explanation is not a little controversial: Because the horn mouth is much closer to the size of the midrange cone than the usual tweeter dome, this creates (Triangle claims) smoother energy transfer through the crossover transition. It's an interesting concept that may…