VAC 452 iQ review in Stereophile

An extremely enthusiastic subjective review by Michael Fremer - the kind of review that makes people say "I want them!" - followed by a measurement sections showing disappointing very poor measurements of signal to noise ratio by John Atkinson. Should we conclude that poor SNR improves sound quality? ;) The recent review of the new Dan D'Agostino Master Audio Systems Momentum HD line preamplifier also shows a similar behavior - much improved sonics compared to the previous version, but extremely poor measurements of signal to noise ratio, much worst than the ones of the previous model.
 

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Mike Lavigne

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#22

Ron Resnick

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#23
It seems like linearity is no longer the emphasis in boutique designers’ design goals and that they are now “voicing” their equipment for a desired sound. They appear to have also learned a lesson from Halcro, who designed equipment with almost unmeasurable THD (Total Harmonic Distortion) but that not many found musical; and they have now embraced principles of psychoacoustics, where distortion improves detail retrieval and perciveability. This is part of the tools of the trade in the mastering studio world and an unspoken practice in high-end audio, where gullible deep pocket audiophiles are swindled with promises of precision and high-fidelity, while being sold distortion.

Have a read at the following article and see how it reflects the current state of high-end audio:

Analogue Warmth

Some of these much heralded “trophy” gear and designers are cooking the books.
I don't know what all this sarcasm is about. If you have been on WBF a while, then you know that we judge components primarily, if not entirely, by subjective sound quality, and not by measurements or purely by theory.

If your point is, for example, that second harmonic distortion from SET amplifiers leads devotees of horn speakers driven by SET amps astray from their perception of natural sound reproduction, and suggests they are being "swindled" by promises of high-fidelity but in reality are being tricked with deliberate distortion, I think such audiophiles will disagree with you.

From your Analog Warmth article I conclude only that some engineers recording in digital have realized that, measurements aside, they are losing in their recording process some essential elements of what real acoustic music sounds like.
 
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JackD201

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Apr 21, 2010
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#24
I don't see how a big push pull amp from AR, VTL, or VAC, can sound better than a good SS amp in an all out system (i have never heard VAC outside a show, just my assumption it is on the lines of, but different from AR, VTL, or CJ). In all the latter 3 cases I would prefer them to a not so good SS, but not to a good SS. In a system like Mike's, I see no chance for the other 3 to compete with the Dartzeel. Now if such a system gets set around another high quality SS amp like dagostino, boulder or audionet Heisenberg, that is different and would be a good competition
You mean a system that can play both low and intimate and also flap your pant legs without making you scream in pain from grit and glare? Yes they can.
 

bonzo75

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#25
You mean a system that can play both low and intimate and also flap your pant legs without making you scream in pain from grit and glare? Yes they can.
No it just doesn't match the dynamic range, clarity, and drive for speakers that require SS. The bass is thick and distorted. Intimate with big watt push pull on such speakers is a color that keeps repeating. The haze is too high
 

JackD201

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Apr 21, 2010
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#26
No you just have't experienced it for yourself.
 
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analogsa

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Apr 15, 2017
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#27
Not sure i see an issue with the noise performance, it just adds a bit of harmless analogue dithering :)

It also puts in perspective the outrageous and largely pointless achievements of the best dacs today. A dac should really have 60db less noise than a poweramp? For what?

Otoh, the 0.94ohm output impedance of the 453 iQ will make many speakers very unhappy.
 

Carlos269

Well-Known Member
Mar 21, 2012
108
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#28
I don't know what all this sarcasm is about. If you have been on WBF a while, then you know that we judge components primarily, if not entirely, by subjective sound quality, and not by measurements or purely by theory.

If your point is, for example, that second harmonic distortion from SET amplifiers leads devotees of horn speakers driven by SET amps astray from their perception of natural sound reproduction, and suggests they are being "swindled" by promises of high-fidelity but in reality are being tricked with deliberate distortion, I think such audiophiles will disagree with you.

From your Analog Warmth article I conclude only that some engineers recording in digital have realized that, measurements aside, they are losing in their recording process some essential elements of what real acoustic music sounds like.

Ron, it looks like my point went right passed you or you did not grasp what I said in my post. Let me make it clear for you: with tube electronics the norm of 1% THD and second order distortion has historically been accepted. This is not the case for solid state based electronics. In 2020, all competent designers can design solid state amplifiers with vanishing levels of THD%. Just go to DIY Audio, even the amateurs have been designing and building linear solid state amplifiers for decades.

The point about the “swindle” has to do with what you expect to be paying for based on equipment specifications versus what is delivered. This is pretty black and white. You don’t have to believe me, just read John Atkinson’s notes in the measurement section.

There is simply no reason for a well designed solid state amplifier to have high THD% in this age of electronics and component quality, unless it is either intended in the design as a design choice or as a by-product of voicing the final product’s sonic signature. Whatever the case may be, measurements or not, linearity has always been the hallmark of well designed amplifiers, tube or solid state in implementation.

The point of the article is that there are desirable sonic attributes associated with certain types of distortion. There are many AES white-papers on this topic:




Subject: Perception and Psychoacoustics

In this study two so-called -psychoacoustic processors- are examined exemplarily by applying concepts, models, and methods of scientific psychoacoustics. Physical measurements of processed sounds and results of hearing experiments on speech intelligibility and sound quality (Aural Exciter) and loudness (Loudness Maximizer) are presented and discussed with regard to classic psychoacoustic models and potential new applications. Therefore relevant psychoacoustic facts, in particular the perception of nonlinear distortion, are reviewed.

From Wikipedia:

Harmonic content and distortion

Triodes (and MOSFETs) produce a monotonically decaying harmonic distortion spectrum.[clarification needed] Even-order harmonics and odd-order harmonics are both natural number multiples of the input frequency.

A psychoacoustic analysis tells us that high-order harmonics are more offensive than low. For this reason, distortion measurements should weight audible high-order harmonics more than low. The importance of high-order harmonics suggests that distortion should be regarded in terms of the complete series or of the composite wave-form that this series represents. It has been shown that weighting the harmonics by the square of the order correlates well with subjective listening tests. Weighting the distortion wave-form proportionally to the square of the frequency gives a measure of the reciprocal of the radius of curvature of the wave-form, and is therefore related to the sharpness of any corners on it.[7] Based on said discovery, highly sophisticated methods of weighting of distortion harmonics have been developed.[8] Since they concentrate in the origins of the distortion, they are mostly useful for the engineers who develop and design audio amplifiers, but on the other hand they may be difficult to use for the reviewers who only measure the output.[9]

A huge issue is that measurements of objective nature (for example, those indicating magnitude of scientifically quantifiable variables such as current, voltage, power, THD, dB, and so on) fail to address subjective preferences. Especially in case of designing or reviewing instrument amplifiers this is a considerable issue because design goals of such differ widely from design goals of likes of HiFi amplifiers. HiFi design largely concentrates on improving performance of objectively measurable variables. Instrument amplifier design largely concentrates on subjective issues, such as "pleasantness" of certain type of tone. Fine examples are cases of distortion or frequency response: HiFi design tries to minimize distortion and focuses on eliminating "offensive" harmonics. It also aims for ideally flat response. Musical instrument amplifier design deliberately introduces distortion and great non-linearities in frequency response. Former "offensiveness" of certain types of harmonics becomes a highly subjective topic, along with preferences towards certain types of frequency responses (whether flat or un-flat).

Push–pull amplifiers use two nominally identical gain devices in tandem. One consequence of this is that all even-order harmonic products cancel, allowing only odd-order distortion.[10] This is because a push–pull amplifier has a symmetric (odd symmetry) transfer characteristic. Power amplifiers are of the push-pull type to avoid the inefficiency of Class A amplifiers.

A single-ended amplifier will generally produce even as well as odd harmonics.[11][12][13] A particularly famous research about "tube sound" compared a selection of single-ended tube microphone preamplifiers to a selection of push-pull transistorized microphone preamplifiers.[14] The difference in harmonic patterns of these two topologies has henceforth been often incorrectly attributed as difference of tube and solid-state devices (or even the amplifier class). Push–pull tube amplifiers can be run in class A (rarely), AB, or B. Also, a class-B amplifier may have crossover distortion that will be typically high order and thus sonically very undesirable indeed.[15]

The distortion content of class-A circuits (SE or PP) typically monotonically reduces as the signal level is reduced, asymptotic to zero during quiet passages of music.[16] For this reason class-A amplifiers are especially desired for classical and acoustic music since the distortion relative to signal decreases as the music gets quieter. Class-A amplifiers measure best at low power. Class-AB and B amplifiers measure best just below max rated power.
 
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Alpinist

Well-Known Member
Jun 17, 2014
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#30
my speakers are 97db, with a nominal 7 ohm load. they mostly run at 1-2 watts output with the 458's or 468's.

when i'm really cranking it i see steady state levels of 25-75 watts and occasional peaks of 200-300 watts.

i've been at shows with Herve where is pushed 458's and 468's to 1200 peak watts with 86db efficient speakers.
Hi Mike,

Thanks for your responses. Respectfully, I did read the manufacturer’s comments but I don’t believe this accounts for the differential of 900 watts at 4 ohms on the NHB-458 versus 205 watts at 4 ohms on the NHB-468 per JA’s measurements. These power limitations would make the NHB-468 a non-starter in my system because my Vandersteen 7 Mk2’s have a nominal impedance of 4 ohms and 83.5 dB sensitivity. The NHB-458’s, on the other hand, would have been ideal. Nevertheless, I’m happy to hear the NHB-468’s are working great in your system and you are a satisfied customer.

Best,
Ken
 
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Mike Lavigne

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Apr 25, 2010
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#31
No it just doesn't match the dynamic range, clarity, and drive for speakers that require SS. The bass is thick and distorted. Intimate with big watt push pull on such speakers is a color that keeps repeating. The haze is too high
that is what i hear with big tubes in my system when pushed, coloration get's exposed. and it's only when you hear how it can be done with the big darts when it fully unleashes the music that you realize you simply don't have to settle for that coloration. you get reminded it's a reproduction to a higher degree. with the darts the amplifier headroom with my speakers is considerable.

ultimately big tubes are limiting......however wonderful they are on their own. as i wrote earlier, the big VAC's would be a great 'forever' amp in my system. i just prefer something else even more.
 

the sound of Tao

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Jul 18, 2014
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#32
Ron, it looks like my point went right passed you or you did not grasp what I said in my post. Let me make it clear for you: with tube electronics the norm of 1% THD and second order distortion has historically been accepted. This is not the case for solid state based electronics. In 2020, all competent designers can design solid state amplifiers with vanishing levels of THD%. Just go to DIY Audio, even the amateurs have been designing and building linear solid state amplifiers for decades.

The point about the “swindle” has to do with what you expect to be paying for based on equipment specifications versus what is delivered. This is pretty black and white. You don’t have to believe me, just read John Atkinson’s notes in the measurement section.

There is simply no reason for a well designed solid state amplifier to have high THD% in this age of electronics and component quality, unless it is either intended in the design as a design choice or as a by-product of voicing the final product’s sonic signature. Whatever the case may be, measurements or not, linearity has always been the hallmark of well designed amplifiers, tube or solid state in implementation.

The point of the article is that there are desirable sonic attributes associated with certain types of distortion. There are many AES white-papers on this topic:




Subject: Perception and Psychoacoustics

In this study two so-called -psychoacoustic processors- are examined exemplarily by applying concepts, models, and methods of scientific psychoacoustics. Physical measurements of processed sounds and results of hearing experiments on speech intelligibility and sound quality (Aural Exciter) and loudness (Loudness Maximizer) are presented and discussed with regard to classic psychoacoustic models and potential new applications. Therefore relevant psychoacoustic facts, in particular the perception of nonlinear distortion, are reviewed.

From Wikipedia:

Harmonic content and distortion

Triodes (and MOSFETs) produce a monotonically decaying harmonic distortion spectrum.[clarification needed] Even-order harmonics and odd-order harmonics are both natural number multiples of the input frequency.

A psychoacoustic analysis tells us that high-order harmonics are more offensive than low. For this reason, distortion measurements should weight audible high-order harmonics more than low. The importance of high-order harmonics suggests that distortion should be regarded in terms of the complete series or of the composite wave-form that this series represents. It has been shown that weighting the harmonics by the square of the order correlates well with subjective listening tests. Weighting the distortion wave-form proportionally to the square of the frequency gives a measure of the reciprocal of the radius of curvature of the wave-form, and is therefore related to the sharpness of any corners on it.[7] Based on said discovery, highly sophisticated methods of weighting of distortion harmonics have been developed.[8] Since they concentrate in the origins of the distortion, they are mostly useful for the engineers who develop and design audio amplifiers, but on the other hand they may be difficult to use for the reviewers who only measure the output.[9]

A huge issue is that measurements of objective nature (for example, those indicating magnitude of scientifically quantifiable variables such as current, voltage, power, THD, dB, and so on) fail to address subjective preferences. Especially in case of designing or reviewing instrument amplifiers this is a considerable issue because design goals of such differ widely from design goals of likes of HiFi amplifiers. HiFi design largely concentrates on improving performance of objectively measurable variables. Instrument amplifier design largely concentrates on subjective issues, such as "pleasantness" of certain type of tone. Fine examples are cases of distortion or frequency response: HiFi design tries to minimize distortion and focuses on eliminating "offensive" harmonics. It also aims for ideally flat response. Musical instrument amplifier design deliberately introduces distortion and great non-linearities in frequency response. Former "offensiveness" of certain types of harmonics becomes a highly subjective topic, along with preferences towards certain types of frequency responses (whether flat or un-flat).

Push–pull amplifiers use two nominally identical gain devices in tandem. One consequence of this is that all even-order harmonic products cancel, allowing only odd-order distortion.[10] This is because a push–pull amplifier has a symmetric (odd symmetry) transfer characteristic. Power amplifiers are of the push-pull type to avoid the inefficiency of Class A amplifiers.

A single-ended amplifier will generally produce even as well as odd harmonics.[11][12][13] A particularly famous research about "tube sound" compared a selection of single-ended tube microphone preamplifiers to a selection of push-pull transistorized microphone preamplifiers.[14] The difference in harmonic patterns of these two topologies has henceforth been often incorrectly attributed as difference of tube and solid-state devices (or even the amplifier class). Push–pull tube amplifiers can be run in class A (rarely), AB, or B. Also, a class-B amplifier may have crossover distortion that will be typically high order and thus sonically very undesirable indeed.[15]

The distortion content of class-A circuits (SE or PP) typically monotonically reduces as the signal level is reduced, asymptotic to zero during quiet passages of music.[16] For this reason class-A amplifiers are especially desired for classical and acoustic music since the distortion relative to signal decreases as the music gets quieter. Class-A amplifiers measure best at low power. Class-AB and B amplifiers measure best just below max rated power.
Ron I hope you feel appropriately chastised now... that Wikipedia quote was pretty darn compelling... just when will you give up on your naively romantic and musically subjectivist ways :eek:
 

bonzo75

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Feb 26, 2014
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#33
that is what i hear with big tubes in my system when pushed, coloration get's exposed. and it's only when you hear how it can be done with the big darts when it fully unleashes the music that you realize you simply don't have to settle for that coloration. you get reminded it's a reproduction to a higher degree. with the darts the amplifier headroom with my speakers is considerable.

ultimately big tubes are limiting......however wonderful they are on their own. as i wrote earlier, the big VAC's would be a great 'forever' amp in my system. i just prefer something else even more.
Agreed. They sound good on the first few records due to the tubey feeling but there is nothing more.
 

JackD201

WBF Founding Member
Apr 21, 2010
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#34
The reason II went SS is that sometimes I just really want to push things. Too many B+ fuses blown for me to go for it without worry setting in eeven before things start heading south. That said I have experienced my old speakers with Vacs and Sigfriied 1 and 2s, alone and bi-amped. Also with Jim's 111s. No slop at concert levels. Sensitivity of 96 and flat at 6. Ron and Steve have both heard my old 11s on only 200wpc hybrids doing my jazz club impressions. Steve has heard the 111s doing the concert hall thing with the IQs, Siegfriied. Mike needed 2 108s for the older Mk1 little brother he owned before his MM3s. I needed 4 Monoblocks. Only one pair with the big brother. Sadly the DX100, one of my favorite amps can't handle my old or current speakers. I know the IQ can in my room and showgoers seem to agree the last four years in a gargantuan ballroom that 2 pairs of them can. Again, too many B+ fuses for me to worry about so M10 it is when this whole pandemic settles down.
 

bonzo75

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Feb 26, 2014
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#35
Like I said, I haven't heard the VAC. I compared the VTL S400 to spectral 400 on XLF and VTL were outclassed on all aspects.

I compared the 750 to the MSB 204 and though I preferred the VTL there, on the top TAD floorstander, I will take a dagostino, gryphon, boulder, etc any day. For those that don't need such drive, there is Dartzeel, then Berning quadratures (which has tubes).

Even with Martin Logan which does well with tubes I prefer SS amp and the tubes should be upstream.

The tube amp that sounds better than all these push pull amps (AR, VTL, CJ) to me is the KR VA 200.
 
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Mike Lavigne

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Apr 25, 2010
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#36
The reason II went SS is that sometimes I just really want to push things.
and unless you've had an approach where you have a system and space to allow the music to fully breathe, extend and scale it's hard to relate to this idea. not for the casual person. when you really (and i mean REALLY) push you discover why you paid attention to all those details and took your room acoustically to another level.

there is no replacement for displacement.

big, high quality, solid state can just do stuff.
 

bonzo75

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Feb 26, 2014
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#37
and unless you've had an approach where you have a system and space to allow the music to fully breathe, extend and scale it's hard to relate to this idea. not for the casual person. when you really (and i mean REALLY) push you discover why you paid attention to all those details and took your room acoustically to another level.

big, high quality, solid state can just do stuff.
By pushing, it does not mean loud volume. For some reason after Mike preferred the Dartzeel to the other tubes, tube fans started the "Mike listens on warp 9 hence..."
 

Mike Lavigne

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Apr 25, 2010
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#38
By pushing, it does not mean loud volume. For some reason after Mike preferred the Dartzeel to the other tubes, tube fans started the "Mike listens on warp 9 hence..."
agree, it's not that i need 100db/110db of volume, it means when i am playing music at 'live' levels the system can have that 'jump' factor and vivid naturalness and be full frequency and everything holds together and scales effortlessly. each musical thread is able to fully propagate. the sound stage is continuous. nuance, tone and timbre all in play. no congealing or sense of hesitation.

big tubes when pushed begin to gloss over detail and nuance; once that starts to happen i lose a degree of musical involvement. i get bored, want to turn it down. it's not fun.

i want to have fun. and since i can have fun.....i do.
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
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#39
No it just doesn't match the dynamic range, clarity, and drive for speakers that require SS. The bass is thick and distorted. Intimate with big watt push pull on such speakers is a color that keeps repeating. The haze is too high
I understand that you reject any component that homogenizes sound, and applaud any component that allows the differences in the sounds of music (and the differences in the sounds of other components) to be most easily discerned and identified.

I am just not sure that this should be a universal prime directive, elevated above other (or all other) parameters, or that the answer to your question necessarily solves for one's personal sonic objective for the hobby of high-end audio.
 

bonzo75

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Feb 26, 2014
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#40
agree, it's not that i need 100db/110db of volume, it means when i am playing music at 'live' levels the system can have that 'jump' factor and vivid naturalness and be full frequency and everything holds together and scales effortlessly. each musical thread is able to fully propagate. the sound stage is continuous. nuance, tone and timbre all in play. no congealing or sense of hesitation.

big tubes when pushed begin to gloss over detail and nuance; once that starts to happen i lose a degree of musical involvement. i get bored, want to turn it down. it's not fun.

i want to have fun.
Exactly. Imo when people don't agree to this entry don't appreciate drive of a note, how it has to extend all the way through, and dynamic range. They focus too much on the harmonic feeling only of tube decay, and the initial feeling of air when you get tubes in
 

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