When you flip on the rear-mounted power switch, three lights go on in sequence: The first indicates Power to the unit, the second that Voltage has been applied…
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Using the M150s was simple. Speaker connection is via five-way TIFF binding posts, and there's a gold-plated RCA jack on the rear for the input. An IEC jack allows you to play with AC cables, and there's an AGC 6 speaker-output protection fuse that you can change, depending on what power your speakers can handle. If your "audio guru" tells you such fuses are "directional," go for it! I didn't touch the fuses in my review samples.
But let's go back to the positives I heard from the M150s that first time in Las Vegas and in every listening session at home: The amplifiers were superbly well organized in time. They were rhythmically coherent, creating a correct sense of musical organization. And yes, they were "liquid," sounding neither "tubey" nor "solid-state." I have to agree with Herron's assessment of his amplifier: To me, it sounded remarkably neutral tonally and harmonically, extremely well-focused without etch or grain, and offered the low-frequency control of a good solid-state amp and the smooth, liquid detail…
Sidebar 1: Specifications
Description: Solid-state monoblock power amplifier. Output power: 150Wpc at 1kHz into 8 ohms (21.8dBW), 275Wpc at 1kHz into 4 ohms (21.4dBW). Frequency response: 20Hz-20kHz, ±1dB. THD: not specified. Voltage gain: 24dB. Input impedance: 47k ohms. Input sensitivity: not specified. Absolute polarity: Non-inverting. Power consumption: not specified.
Dimensions: Amplifier: 19" W by 4" H by 10.5" D. Weight: 25 lbs.
Price: $5895/pair. Approximate number of dealers: 15. Warranty: 2 years parts & labor.
Manufacturer: Herron Audio, Division of Herron…
Sidebar 2: Associated Equipment
Analog sources: Simon Yorke turntable, Graham 2.0 and Immedia RPM2 tonearms, Lyra Parnassus DCt and Lyra Helikon cartridges.
Digital source: Naim CD-5 CD player with Naim FlatCap 2 power supply.
Preamplification: Audio Research Reference and Herron VTPH-1A phono sections, Herron VTSP-1A line preamplifier, Hovland HP-100 and Ayre K-1x preamplifiers.
Loudspeakers: Sonus Faber Amati Homage, Audio Physic Rhea subwoofer.
Cables: DIN/RCA: Hovland Music Groove. Interconnect: Harmonic Technology Pro-Silway II, Herron Audio. AC: Chord, Nordost (Naim…
Sidebar 3: Measurements
Before I measure a power amplifier, I precondition it by running it at one-third power for an hour. This maximally stresses a design with a class-B or -AB output stage. After this period, the Herron M150's heatsink was too hot to touch, though the chassis was still cool by comparison. The amplifier's input impedance measured a usefully high 46.4k ohms at 1kHz, and as specified, it didn't invert signal polarity. The M150's voltage gain into 8 ohms was a low 24.3dB—this will be a problem with passive volume controls, as some CD players will be unable to drive the…
However, when I examined the distortion content, I was surprised to see—superimposed over what appears to be basically a third harmonic (fig.4)—what looks like crossover distortion. (The spikes in this 'scope trace occur at exactly the zero-crossing points of the sinewave.) Yes, the measured level in this graph is very low (0.003%), but crossover distortion tends to be more audible than its level would imply, due to its high-order content and the fact that it tends to dominate at low signal levels. At high powers (fig.5), it tends to drop into insignificance. Intermodulation distortion was…
Manufacturer's Comment
Editor: I want to thank Michael Fremer and John Atkinson for their time spent evaluating the M150 amplifier. I also want to thank Michael particularly for his warm hospitality and a fun afternoon during my visit. He has an amazing record collection.
I was disappointed to see by John's measurements that the idle current of the M150 review samples had been set slightly on the low side at the factory, resulting in the crossover notch shown in fig.4. This would have taken away from the transparency of the units.
The higher price tags of many of today's…
Michael Fremer wrote a Followup in November 2001 (Vol.24 No.11):
You'd really have to be in an audio critic's shoes to understand the embarrassment of reading your own rave review in Stereophile, only to glance down at the "Measurements" Sidebar to find that the product fared so poorly on John Atkinson's test bench that it might very well have been defective. It's like emerging from cold water onto a crowded beach and having your bathing suit come off. Measurements don't tell the whole story, as any vinyl- or tube-loving audiophile will attest, but sometimes the graphs offer…
One room at the 1999 CES in Las Vegas that knocked me for a loop was the Avalon/Classé installation mentioned in my April show report. Classé had just debuted the Omega preamp, the companion piece to the Omega amplifier I reviewed in March. It proved a very suave, musical, and high-performance marriage.
Returning from CES, I thought about some of the trends I'd noticed. With the ca $150k Boulder system, the pricey Burmester electronics, and the slew of new X-series components from Pass Labs, there are suddenly a number of no-holds-barred solid-state super rack systems available.…
Using high-quality, gold-plated WBT connectors, inputs and outputs are ranged across the slimline rear panel of the control chassis in balanced XLR (pin 2 hot) and single-ended RCA configurations. There are three inputs and a tape loop for each connector format, along with two pairs of output connectors, also in both formats. Front-panel adjustments include Volume, Mute, Input selection, Power, and Standby. The handsome, weighty remote controls volume, input selection, tape, display characteristics, and mute. You can also turn the Omega power amplifier on and off with the remote when the IR…