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Much of the rest of the dm58's circuitry is said to be based on concepts from microwave and ultra-high-frequency electronics. According to Halcro's US importer, Philip O'Hanlon, were most electrical engineers to examine a schematic of the Halcro, few would even recognize it as being an audio amplifier. Twelve MOSFETs provide the final amplification and are connected to the left side panel, which serves as a chimneying heatsink. The amps run in class-AB biased toward class-A, and fanatical attention has been devoted to ensuring that each section's ultra-low-distortion amplification of the…
Another boundary-stretching aspect of the Halcro's sound was its silence. Its background was not the outer-space void of a stream of digital zeros but the taut, deep silence of an empty concert hall—a living silence just waiting to be energized by sound. I don't know what JA's measurements will show about the dm58's noise floor, but I'd never heard an amplifier this quiet. As a result, detail retrieval bordered on the supernatural. Subway trains running under Kingsway Hall on Decca and EMI LPs? Chairs squeaking? I heard 'em all through the Halcros.
Whether such funky little details…
Not content to set the standard in tonal neutrality and information retrieval, the Halcro offered dynamic performance that mere mortal amps cannot manage. Today, all serious high-end amplifiers have genuine dynamic authority in the bass and midrange, but few are able to track large dynamic variations in the treble and high treble with the same fidelity they bring to the bass and mids (footnote 4). The Halcro could and did, and this decidedly more lifelike dynamic presentation represented a sound different from that of any other amplifier I have heard. There was more treble energy, yes, but…
Sidebar 1: Specifications
Description: Solid-state monoblock power amplifier, with active power-factor correction. Inputs: 1 unbalanced, 1 balanced. Output power: >200W into 8 ohms (23dBW), >350W into 4 ohms (22.4dBW). Distortion: at full power output, all harmonic distortion orders -114dB up to 20kHz (4000 parts per billion or 0.0004%). THD: -128dB at 1kHz, or 400 ppb. Intermodulation products: all -114dB relative to power output for sum of 19+20kHz tones, each delivering 87.5W into 4 ohms or 50W into 8 ohms or SMPTE-IM. Noise: equivalent input noise at input, 5nV/sqrt(Hz). Slew-…
Sidebar 2: Associated Equipment
Analog source: SOTA Cosmos turntable, Graham Engineering 2.2 tonearm, Dynavector DRT XV-1 cartridge.
Digital sources: Classé Omega SACD/CD player, Ayre D-1x CD/DVD-Video player.
Preamplification: Manley Labs Steelhead, Jeff Rowland Design Group Cadence phono stages; Jeff Rowland Design Group Synergy IIi line stage; Ayre K-1x, Atma-Sphere MP-3 preamplifiers.
Loudspeakers: EgglestonWorks Andra II, Silverline Sonata.
Cables: Phono: Cardas Golden Reference, Hovland Music Groove 2. Interconnect: Nordost Valhalla, Wireworld Gold Eclipse 3+, Cardas…
Sidebar 3: Measurements
Following the usual one-hour preconditioning period at 1/3 power into 8 ohms, the Halcro dm58's chassis was cool to the touch, suggesting efficient heatsinking. The input impedance was a usefully high 102k ohms unbalanced and 194k ohms balanced, and the amplifier didn't invert signal polarity through either input. (The XLRs are wired with pin 2 hot.) The voltage gain was higher than average at 33.45dB through the balanced input, and, as expected 6dB lower through the unbalanced input.
The output impedance was a very low 0.06 ohm across most of the…
Fig.6 is a spectrum of the dm58's output at 200W into 8 ohms, taken with a very linear signal generator: the National Instruments NI4451 PCI card that Miller Audio Research uses as one of the platforms for its QC Suite measurement software. The second, third, and fourth harmonics are all between -106dB and -110dB! The summed total of the harmonics is around 0.0008%, but even then, this is not appreciably higher than the level of the residual harmonics present in the NI card's output (0.00055%).
Fig.6 Halcro dm58, spectrum of 1kHz sinewave, DC-10kHz, at 200W into 8 ohms (linear…
Sam Tellig tried the Halcro dm58 monoblocks in June 2003 (Vol.26 No.6):
Wondering what the Triangle Magellan loudspeakers would sound like with cost-no-object amplifiers, I called Philip O'Hanlon, the Halcro distributor, to see if he could supply a pair of dm58 monoblocks. Fortunately, Philip was able to oblige—not only with two dm58s but also with a dm10 preamp to go with them. Unfortunately, I was not able to hold on to the Halcros long enough to review them in their own rights. I can tell you that the preamp's performance is as amazing as that of the amplifier.
What the…
Brian Damkroger wrote about the Halcro dm58 in February 2006 (Vol.29 No.2):
When Paul Bolin reviewed Halcro's dm58 amplifier2 in the October 2002 Stereophile, he pronounced it that rarest of the rare: a truly revolutionary audio product. Its technology was unusual; Philip O'Hanlon of importer On a Higher Note speculated that, "were most electrical engineers to examine a schematic ... few would even recognize it as being an audio amplifier." John Atkinson found it to have "astonishing measured performance for an amplifier," and often felt that he was measuring the limits of his test…
It's always good to tear into a good steak with Tor Sivertsen, Conrad-Johnson's main marketing man.
Tor, who hails from Norway, was for many years the public face of Tandberg in the US. He knows what's important: first food, then hi-fi; first tubes, then transistors. As Tor says, "If you like frozen meat, buy transistor equipment. If you like 21-day aged beef, buy tubes."
We were talking on the phone. "I could have the new Conrad-Johnson MV60 amplifier sent to you," said Tor, "but it will be more fun to hand it to you in the parking lot of the Union House, a new steak…