Vandersteen Model Seven Mk.II loudspeaker & M7-HPA monoblock power amplifier Vandersteen M7-HPA Measurements

Sidebar 4: Vandersteen M7-HPA Measurements

I performed a full suite of measurements on one of the Vandersteen M7-HPA amplifiers (serial no.107), using my Audio Precision SYS2722 system (see www.ap.com and the January 2008 "As We See It"). I preconditioned the amplifier by running it at one-third the specified power, 100W, into 8 ohms for 60 minutes. At the end of that time, its heatsinks were warm, at 112.4°F (44.7°C). The percentage of THD+noise at this power level was 0.07%.

A note on the measurements: the M7-HPA's hair-trigger protection caused it to shut down several times during the measurements, mostly when I was asking it to drive high powers into low impedances without ramping up the input signal. For example, if I hit the amplifier with a sinewave signal equivalent to a continuous output of 50W into 8 ohms, it went into protection. Every time, turning the amplifier back on brought it successfully back to life. I never had this problem when listening to music.

The Vandersteen's voltage gain at 1kHz into 8 ohms was 24.7dB, and the amplifier preserved absolute polarity (ie, was non-inverting). (The input XLR is wired with pin 2 hot.) The input impedance was very high, ranging from 700k ohms at 20Hz to 210k ohms at 20kHz. The output impedance was a little higher than usual for a design with a solid-state output stage, presumably due to the two output stages being in series with the load, at 0.27 ohm at 20Hz, 0.23 ohm at 1kHz, and 0.25 ohm at 20kHz. This impedance resulted in a response variation of ±0.15dB into our standard simulated loudspeaker (fig.1, gray trace). This graph reveals the high-pass function, with a –3dB point at 90Hz and an ultimate 6dB/octave rolloff—this behavior was the same from both sets of outputs—which results in the expected sloped tops and bottoms with a 1kHz squarewave (fig.2). At the other end of the spectrum, the M7-HPA's response extended to –1.5dB at 200kHz into 8 ohms (fig.1, blue trace), which correlates with the excellent shape of a 10kHz squarewave (fig.3).

Fig.1 Vandersteen M7-HPA, Tweeter Midrange frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (blue), 4 ohms (magenta), 2 ohms (red); Mid Bass Bass frequency response at 2.83V into 8 ohms (green) (1dB/vertical div.).

Fig.2 Vandersteen M7-HPA, small-signal 1kHz squarewave into 8 ohms.

Fig.3 Vandersteen M7-HPA, small-signal 10kHz squarewave into 8 ohms.

The M7-HPA was a little noisier than the norm, the unweighted, wideband signal/noise ratio (ref. 2.83V into 8 ohms and taken with the input shorted to ground) measuring 68.2dB and due primarily to random noise (fig.4). A-weighting the measured ratio improved it to a respectable 93.1dB.

Fig.4 Vandersteen M7-HPA, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms (linear frequency scale).

Figs. 5 and 6 plot the THD+noise percentage against power into 8 and 4 ohms. The M7-HPA clipped (defined as when the THD+N reaches 1%) at 350W into 8 ohms (25.4dBW) and 600W into 4 ohms (24.8dBW), the latter confirming the specified maximum power. Into 8 ohms (fig.5), the THD+N rose in linear fashion as the power increased, starting from a low 0.02% at 100mW, but remained more constant into 4 ohms (fig.6). Fig.7 shows how the THD+N percentage changed with frequency at a moderately high level, 20V, equivalent to 50W into 8 ohms (blue trace), 100W into 4 ohms (magenta), and 200W into 2 ohms (red). To my surprise, the distortion was lower in the midrange and low treble into 2 ohms than it was into the higher impedances.

Fig.5 Vandersteen M7-HPA, distortion (%) vs 1kHz continuous output power into 8 ohms.

Fig.6 Vandersteen M7-HPA, distortion (%) vs 1kHz continuous output power into 4 ohms.

Fig.7 Vandersteen M7-HPA, THD+N (%) vs frequency at 20V into: 8 ohms (blue), 4 ohms (magenta), 2 ohms (red).

The M7-HPA's distortion was predominantly the subjectively benign second harmonic (fig.8), though at high output currents, higher-order harmonics appeared and AC supply-related sidebands can be seen, albeit at low levels (fig.9). These sidebands can also be seen in fig.10, a spectral analysis of the M7-HPA's output as it drove an equal mix of 19 and 20kHz tones at 100W into 4 ohms. Despite the high power, the difference product at 1kHz lies at a low –70dB (0.03%), with very few higher-order spuriae visible.

Fig.8 Vandersteen M7-HPA, 1kHz waveform at 50W into 4 ohms, 0.07% THD+N (blue); distortion and noise waveform with fundamental notched out (red, not to scale).

Fig.9 Vandersteen M7-HPA, spectrum of 1kHz sinewave, DC–10kHz, at 100W into 4 ohms (linear frequency scale).

Fig.10 Vandersteen M7-HPA, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 100W peak into 4 ohms (linear frequency scale).

I was about to write that the M7-HPA measures well for an amplifier with zero loop-negative feedback. Actually, it measures well, period.—John Atkinson

COMPANY INFO
Vandersteen Audio, Inc.
116 W. Fourth Street
Hanford, CA 93230
(559) 582-0324
ARTICLE CONTENTS

COMMENTS
ctsooner's picture

What a great review of an amazing powered speaker system with what sounds like some first ever experiences, especially with some of your own recordings. I must admit though that after reading the conclusion I wondered why you withheld any recommendation for this system. I read your first paragraph and you spoke about getting more that you expected. After rereading your review, I get that same feeling you had with the original 2's. Can you highly recommend this system? Thanks I value your response.

John Atkinson's picture
ctsooner wrote:
After rereading your review, I get that same feeling you had with the original 2's. Can you highly recommend this system?

Yes Indeed. It broke my heart when the shipping company picked it up last week to be returned to Vandersteen. And a full-range version of the Vandersteen M7-HPA monoblock would be a wondrous amplifier indeed!

But there is a certain relief in being back in the land of audio components that I can actually afford!

John Atkinson
Editor, Stereophile

ctsooner's picture

John, thanks so much for responding and sharing your thoughts. The best thing about Vandersteen is that they DO have affordable for nearly anyone as they have a trickle down, signature sound. I converted to them a few years ago as a lower cost of admission and am very happy with them.

Sea Otter's picture

Good to see a designer sticking with his inordinate design criteria, and taking it to it's logical extremes. I believe he has developed what may be the best cone construction in the industry with his carbon/balsa drivers.

While his speakers aren't quite my cup of tea, I certainly respect him as one of the most diligent and talented designers in the industry.

Alpinist's picture

I recently purchased the Vandersteen Model Seven Mk II Speakers and Vandersteen M7-HPA Mono Amps from John Rutan at Audio Connection. John positioned the speakers in my family room using laser sighting and tuned the speakers' powered subwoofers with their 11-band equalization to give an even response in my room across their frequency range.

The ability to tune the bass on these speakers has made them integrate into my room better than any of the other speakers I have previously owned. Consequently, the bass creates the perfect cohesive foundation for the midrange and treble in my listening room. John was also nice enough to loan me an Audio Research Reference CD-9 Digital Player, Audio Research Reference 6 Preamp and AudioQuest Fire Interconnects.

The synergy of the Vandersteen speakers and mono amps, combined with the Audio Research preamp and digital player, has resulted in the highest sound quality I have ever heard and it is occurring right in my non-dedicated listening room!

The Vandersteen/ARC/AQ system is producing amazing tonality. Midrange body, weight and bloom. Tremendous ease without a hint of solid state or digital edge. Vocals and instruments are holographic and float in space with wonderful separation between vocal and instrumental lines. The soundstage, depending on the recording, can be very wide and deep, extending well beyond the walls of my room. Bass is very robust and lifelike with wonderful texture and goes down to subterranean levels. Deep pipe organ notes are felt to the core. It feels like I'm in a cathedral. Female jazz vocals are as smooth as silk with zero sibilance. Trumpets really have that blatt sound. Violins sound like wooden boxes, not glass ones. Dynamics are lightning fast and powerful. The pure silver AudioQuest cabling enhances detail and nuance with no additional treble or midrange brightness.

To sum it up, for the first time ever, I am totally content with the world class sound quality I am enjoying. The system sounds so lifelike, I forget about the components and become totally immersed in the music. I often listen very late into the night, mining my music collection to rediscover old favorites. Mr. Vandersteen, you hit it out of the ballpark with this speaker/amp combo!

JimboJumbo's picture

There's a bit of resonant activity around 4 or 5 Khz and also 18 Khz in the CSD plot.

Step response is spot on; see my comments on the Wilson audio test; https://www.stereophile.com/content/wilson-audio-specialties-alexx-loudspeaker#comment-576416

Other stuff looks pretty good; but then for $62K it should be.

JimboJumbo's picture

Slew rate?

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