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iFi adds the "Even-Order Harmonics that All Music Lovers Crave"


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Chinese equipment maker Yaqin has had several "tube buffers" of this type on sale for quite a while at different price points. So the idea is hardly new.

 

YAQIN SD CD3 6N8P Tube Signal Upgrade Hi End Buffer Processor for CD Player | eBay

 

 

 

I used to be a big tube fan. "The sweet, open sound of tubes" was my mantra. At that time, my system consisted of an Audio Research SP-11 feeding a pair of VTL-140 mono-blocks (each amp used six pre-war designed 807 transmitter tubes for 140 Watts!). Then I was asked review a Krell KAV-300i integrated, when I heard how clean and accurate-sounding the Krell was, I fell "out of love" with my heretofore beloved tube gear and sold it. Yeah, tubes can sound seductive, no doubt, but to me that Krell was a revelation about how good solid-state CAN be. I don't think I would want to go back to tubes for my main system (my computer room audio system has a hybrid tube/transistor amp though (Napa NA-208A). it sounds nice on streaming Internet radio).

George

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:) and I just sold my Krell amp for a custom made tube amp! I think the ideal situation is 2 systems.

 

Interesting. I didn't keep the Krell, BTW, it was a review sample and had to go back to the mfg. Later, I reviewed the Harman Kardon HK-990 Integrated amp. This amp was more flexible than the Krell, and sounded better for less money, so I bought it. It is a dual mono design (with separate power supplies - including individual torroidal power transformers, one for each channel) with 150 W/channel, sports a built-in dual differential 24/192 DAC, a MM/MC phono stage, an A/D (for digitizing analog sources!) and a computerized room optimization system. It has lots of inputs and any one can be configured (from the remote control) as a RCA analog source, two RCA digital sources, or two TOSLINK sources, so it is possible to use one input for several different components simultaneously! It also sports several record-outputs both digital and analog. Soundwise, it blows the Krell KAV-300i out of the water and sounds superb (Stereophile rated it as a sold class-B component in their yearly ratings, and that ain't shabby - for whatever that's worth), and as far as I'm concerned the only think H-K missed was a USB audio input! I am very happy with it.

George

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Interesting. I didn't keep the Krell, BTW, it was a review sample and had to go back to the mfg. Later, I reviewed the Harman Kardon HK-990 Integrated amp. This amp was more flexible than the Krell, and sounded better for less money, so I bought it. It is a dual mono design (with separate power supplies - including individual torroidal power transformers, one for each channel) with 150 W/channel, sports a built-in dual differential 24/192 DAC, a MM/MC phono stage, an A/D (for digitizing analog sources!) and a computerized room optimization system. It has lots of inputs and any one can be configured (from the remote control) as a RCA analog source, two RCA digital sources, or two TOSLINK sources, so it is possible to use one input for several different components simultaneously! It also sports several record-outputs both digital and analog. Soundwise, it blows the Krell KAV-300i out of the water and sounds superb (Stereophile rated it as a sold class-B component in their yearly ratings, and that ain't shabby - for whatever that's worth), and as far as I'm concerned the only think H-K missed was a USB audio input! I am very happy with it.

 

Is that thing turbocharged?

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All gear has distortion, and lower order distortion is more benign than higher order distortion. You cannot equally weight their contribution, or lump them into one "distortion" bin. I think a lot of tube owners would rather have higher levels of low order distortion than lower total or high order distortion.

 

I would say by and far it isn't that tube lover want to add distortion. That is usually what someone who wants to be provocative says...

A Digital Audio Converter connected to my Home Computer taking me into the Future

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Is that thing turbocharged?

 

Makes you wonder, doesn't it? It sure is feature-laden all right and I couldn't be happier with the sound. I recently had a chance to compare the HK-990 with a Pass Labs INT-150 integrated. Same power rating as the H-K, but nowhere near as flexible or as feature full. I don't think it sounded as good either. While specs are similar, I found the presentation of upper midrange and highs to be superior with the H-K and the bass tighter with more impact. Of course, the Pass was cosmetically better built, with WBT-style RCAs instead of the more mass-market gold-plated RCAs on the H-K. But, of course, the Pass INT-150 sells for more than $7K as opposed to the HK-990 which retails at about $2500. I'll put up with the cheaper RCA jacks for the price difference, thank you.

George

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All gear has distortion, and lower order distortion is more benign than higher order distortion. You cannot equally weight their contribution, or lump them into one "distortion" bin. I think a lot of tube owners would rather have higher levels of low order distortion than lower total or high order distortion.

 

I would say by and far it isn't that tube lover want to add distortion. That is usually what someone who wants to be provocative says...

 

Sorry, I am not familiar with the terms "lower order" and "higher order" distortion, By lower order do you mean odd-order distortion and by higher-order, do you mean even-order distortion? From context, it looks like that's what you are trying to say. If you mean something else, please elucidate. Thanks.

George

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Lower I'd consider 2nd and 3rd, and higher being 7th, 8th, and 9th.

 

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/amp.html

 

Take my Class-A Pass Int-30A even when driven really hard it starts to generate 2nd and 3rd. You could almost consider it "tube like" in its distortion signature. Let's put it this way... if there was a distortion type design consideration I'd easily trade-off 10x more 2nd order harmonic distortion vs. 7th.

 

High-order harmonic, pre-ring, and quantization distortion all suck.

 

Sorry, I am not familiar with the terms "lower order" and "higher order" distortion, By lower order do you mean odd-order distortion and by higher-order, do you mean even-order distortion? From context, it looks like that's what you are trying to say. If you mean something else, please elucidate. Thanks.

A Digital Audio Converter connected to my Home Computer taking me into the Future

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If I was to make a visual analogy I would say 2nd order is the light from a fireplace or candlelight, 3rd order would be moonlight, 7th order would be LED light, and 9th order would be flickering, cool white cubicle fluorescents.

A Digital Audio Converter connected to my Home Computer taking me into the Future

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Sorry, I am not familiar with the terms "lower order" and "higher order" distortion, By lower order do you mean odd-order distortion and by higher-order, do you mean even-order distortion?

That confused me too. It seems to be widely accepted that even order distortion, even 2nd harmonic, is more benign sounding and even preferable to some, and an excess of odd order harmonics results in harshness.

Hugh Dean from Aspen Audio even manipulates the relatively low distortion of his SS amplifiers to have more even order distortion than low order distortion to give them a small amount of added warmth.

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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https://passlabs.com/articles/audio-distortion-and-feedback

 

 

Harmonic Distortion and Sound

 

Many audiophiles believe that 2nd harmonic is to be preferred over 3rd harmonic. Certainly it is simpler in character, and it is well agreed that orders higher than third are more audible and less musical. However when given a choice between the sound of an amplifier whose characteristic is dominantly 2nd harmonic versus 3rd harmonic, a good percentage of listeners choose the 3rd.

I have built many examples of simple 2nd and 3rd harmonic “types” of amplifiers over the last 35 years. When I say “types” I mean that they used simple Class A circuits described as “single-ended” versus “push-pull” and so tended to have a 2nd harmonic versus 3rd harmonic in the character of their distortion, but were not made to deliberately distort.

Anecdotally, it appears that preferences break out roughly into a third of customers liking 2nd harmonic types, a third liking 3rd harmonic, and the remainder liking neither or both. Customers have also been known to change their mind over a period of time.

However the issue is partially obscured by the fact that the 3rd harmonic type amplifiers usually have lower total distortion. Third harmonic usually appears with a negative coefficient, resulting in what we think of as “compressive” - the example in figure 3. It's worth noting that odd orders on nonlinearity also can be seen altering the amplitude of the fundamental tone -something a distortion analyzer doesn't ordinarily display.

Audiophiles have been accused of using 2nd or 3rd harmonic distortion as tone controls to deliberately alter the sound. I suppose that there are people who like it that way, but I don't think this is generally the case. For reasons which will become clearer when we talk about inter-modulation distortion, high levels of any harmonic become problematic with musical material having multiple instruments, and the argument that 2nd or 3rd adds “musicality” doesn't quite hold up.

The sound of 2nd order type circuits is often praised as “warm” and by comparison 3rd order type circuits are often noted for “dynamic contrast”. 2nd order type amplifiers seem to do particularly well with simple musical material, and 3rd order types generally seem to be better at more complex music. Figure 4 shows a distortion curve of two power stages operated without feedback – the blue is single-ended Class A, the red is a push-pull Class A.

fig_4_distortion_in_single-ended_vs_push-pull.png

In Figure 4 we see that the 2nd order type declines inversely to the output voltage (the square root of power), and the 3rd order type declines inversely to the square of the voltage (inversely proportional to power). There may be also a relation between this and the perception of “warmth” versus “dynamics”, but it is not clear to me at this time.

Nevertheless, whether you prefer 2nd or 3rd order type amplifiers, let's agree that we wish to minimize the total amount of distortion. And assuming that we have to put up with some distortion let's also agree that we prefer 2nd and 3rd harmonic components over 4th, 5th, 6th, 7th and so on.

A Digital Audio Converter connected to my Home Computer taking me into the Future

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We need to remember here that Nelson Pass amplifiers use FETs which are renowned for a small amount of added warmth.

I have constructed several FET based amplifiers, one with 100W/Ch. 8 ohms, and the other 240W/Ch. 8 ohms.

I didn't like the added warmth, especially on male voice which reminded me a little of an AM radio announcer in his booth vs. an FM radio announcer, and much prefer the sound of a very low distortion Class A SS bipolar transistor amplifier.

Nelson Pass certainly has a large following, but so do Audio Amplifier authors and designers such as Douglas Self who prefers bipolar transistor amplifiers and states why in his books. Douglas Self also designs amplifiers where the distortion is so low that these things don't matter so much.

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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Is your point that we all like low distortion? To that I think we can all agree.

 

Or it that high order harmonics are not bad? Or not more objectionable than low order harmonics? To this I would have to strongly disagree.

A Digital Audio Converter connected to my Home Computer taking me into the Future

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Is your point that we all like low distortion? To that I think we can all agree.

Actually, some don't like amplifiers with very low distortion, as they sound too bland and unexciting to them.

I have even heard the word "feral" used to describe some amplifiers with much higher levels of harmonics that some find more like a live performance..

It all comes down to the "tailoring" of the harmonics. Normally the higher order harmonics are at a MUCH progressively lower level .Many of the Douglas Self type amplifiers have distortion levels approaching 4 Zeroes. Some of the Halcro amplifiers do have 4 zeroes.

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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Is your point that we all like low distortion? To that I think we can all agree.

 

Or it that high order harmonics are not bad? Or not more objectionable than low order harmonics? To this I would have to strongly disagree.

 

One doesn't have to go too far up the fundamental frequency graph before 7th, 8th, and 9th order distortions are out of the audio passband. For instance, at 12 KHz you can introduce many percent of 2nd order distortion and I defy anyone to hear it! And in a 16-bit/44.1 KHz system, it's above the passband!

George

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Actually, some don't like amplifiers with very low distortion, as they sound too bland and unexciting to them.

I have even heard the word "feral" used to describe some amplifiers with much higher levels of harmonics that some find more like a live performance..

It all comes down to the "tailoring" of the harmonics. Normally the higher order harmonics are at a MUCH progressively lower level .Many of the Douglas Self type amplifiers have distortion levels approaching 4 Zeroes. Some of the Halcro amplifiers do have 4 zeroes.

 

A French company, Jadis, in the 1980's built a (expensive) tube amp that had more than 2% THD at half power. It was, at the time, considered one of the best sounding amplifiers on the market. So, it seems that there is distortion, and then there is distortion. I'll guarantee you that an SS amp with that much distortion would be very unpleasant to listen to...

George

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I'll guarantee you that an SS amp with that much distortion would be very unpleasant to listen to...

 

Some SS amplifiers with less than .01 % distortion can be quite unpleasant to listen to for too long. Fatiguing!

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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I heard even -90db of high order distortion has a metallic, grainy character.

 

I was think that today... 1% distortion is the usually of definition of "clipping". 1% low order in a tube design is pretty typical, but 1% with solid-state and you'd want to cup your hands over your ears in the fetal position.

A Digital Audio Converter connected to my Home Computer taking me into the Future

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I heard even -90db of high order distortion has a metallic, grainy character.

 

I was think that today... 1% distortion is the usually of definition of "clipping". 1% low order in a tube design is pretty typical, but 1% with solid-state and you'd want to cup your hands over your ears in the fetal position.

 

No, clipping is different. 1% THD is often the distortion figure at which many amplifier manufacturers traditionally chose to rate their amp's output (especially in the days before transistors), and it is quite a bit short of clipping. 1% THD in an amplifier is generally quite benign, and if it is mostly comprised of even-order distortion, most listeners will not even recognize that level of non-linearity as distortion at all. Clipping is the point where for any increase in input, there stops being an increase in output in an amplifier circuit. On an oscilloscope, clipping looks like a sharp flattening of both the tops and the bottoms of the waveform being amplified. It sounds dreadful. Not just bad, you understand, but truly awful. Even so, tube clipping generally does not sound quite as bad as bipolar transistor clipping because tubes "taper-off" their conduction as they approach the limits of their power supplies, while transistors will amplify more or less linearly right up to the point where the devices "bang" against the voltage limit of their power supply rails. However, any form of clipping in a linear amplifier (of any type of signal) is something to generally be avoided.

 

An interesting experiment is to take both a tube and a transistor amplifier circuit (doesn't have to be a power amp, any simple amplifier stage will work) and hook each up, in turn, to a sine-wave generator and an oscilloscope. Set the generator at 400 Hz, and crank up the generator's output while watching the 'scope. the amps output will appear on the 'scope to continue to increase linearly with the input until the amps start to get overloaded. The tops of the tube amps' sine wave will, at some point, start to change shape. The waveform will lose it's classic sine wave shape and will start to round-off at the top and the bottom in an odd way. Eventually, if you keep cranking up the input single's amplitude the top will start to flatten. This is a tube transfer characteristic, and results in what is often called "soft-clipping". The transistor amp, OTOH, will react quite differently. Again, the output will increase linearly with the increased input amplitude until the transistors become saturated - or fully "on". At this point, the waveform tops and bottoms just flatten. They don't get any higher, the flat part at the tops and bottoms of the waveform just get wider the more you continue to increase the input amplitude. This is not good for audio, but this same characteristic makes transistors ideal as electronic switches. Take a small voltage, and apply it to the transistor's 'base' and the collector-to-emitter voltage becomes essentially the same as the power supply voltage. This ability to use a small DC current to turn-on and off a much larger DC current is a very useful function in many fields of electronics.

George

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This article on the issues of THD, even and odd order harmonics, and IM is very interesting.

 

The Sound of the Machine

 

Some selected quotes:

 

As mentioned above, odd and even harmonics can be recast as asymmetric distortion and symmetric distortion, thus the very different effects seen with IM distortion tests. As D.E.L. Shorter of the BBC pointed out in the April 1950 Issue of Electrical Engineering, real music is dominated by a great many closely-spaced tones - a choir or massed violins having the most dense spectra of all. Shorter showed that with a few as three closely spaced tones, IM sum-and-difference sidebands outnumber the much simpler harmonic series. In effect, as the number of tones increase, the number of IM sidebands increase at much faster rate than simple harmonics. The boundary case is 3 tones of equal magnitude; for 2 tones, IM is about the same as harmonic distortion, for 4 tones, IM is far greater than harmonic distortion. I leave it to the imagination of the reader to figure out how many simultaneous tones are present in real music — a lot more than three!

 

Norman Crowhurst wrote a fascinating analysis of feedback multiplying the order of harmonics, which has been reprinted in "Glass Audio," Vol 7-6, pp. 20 through 30. He starts with one tube generating only 2nd harmonic, adds a second tube in series (resulting in 2nd, 3rd, and 4th), and then makes the whole thing push-pull (resulting in 3rd, 5th, 7th, and 9th), and last but not least, adds feedback to the circuit, which creates a series of harmonics out to the 81st. All of this complexity from "ideal" tubes that only create 2nd harmonic!

 

With real devices there are even more harmonics. In terms of IM, actual amplifiers have complex and dynamic noise floors thanks to the hundreds of sum-and-difference IM terms. That's not even counting the effects of reactive loads, which adds a frequency dependency to the harmonic structure! (With reactive loads, additional harmonics appear due to the elliptical loadline seen by the power tubes. The elliptical load-line dips into the very nonlinear low-current region, resulting in an instantaneous increase in upper harmonics. This spectral "roughening" is most audible with strong low frequency program material and hard-to-drive horn or vented bass drivers.)

 

As Crowhurst noted, feedback mostly reduces the 2nd and 3rd harmonics, leaving the upper ones more or less alone, or sometimes even greater than before. Feedback fools the simple THD meter, but the spectrum analyzer sees through the shell game. Too bad raw power and almost useless THD measurements became the end-all and be-all for more than 50 years. If more engineers and reviewers had access to spectrum analyzers, the misleading nature of raw THD measurements would have been discovered earlier, and amplifier design might have taken a different course.

 

I think it gets to a lot of the points being made in this thread. Comments/thoughts from the article by those qualified to have a practical opinion would be great.

 

Best,

John

Positive emotions enhance our musical experiences.

 

Synology DS213+ NAS -> Auralic Vega w/Linear Power Supply -> Auralic Vega DAC (Symposium Jr rollerball isolation) -> XLR -> Auralic Taurus Pre -> XLR -> Pass Labs XA-30.5 power amplifier (on 4" maple and 4 Stillpoints) -> Hawthorne Audio Reference K2 Speakers in MTM configuration (Symposium Jr HD rollerball isolation) and Hawthorne Audio Bass Augmentation Baffles (Symposium Jr rollerball isolation) -> Bi-amped w/ two Rythmic OB plate amps) -> Extensive Room Treatments (x2 SRL Acoustics Prime 37 diffusion plus key absorption and extensive bass trapping) and Pi Audio Uberbuss' for the front end and amplification

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No, clipping is different. 1% THD is often the distortion figure at which many amplifier manufacturers traditionally chose to rate their amp's output (especially in the days before transistors), and it is quite a bit short of clipping. 1% THD in an amplifier is generally quite benign, and if it is mostly comprised of even-order distortion, most listeners will not even recognize that level of non-linearity as distortion at all. Clipping is the point where for any increase in input, there stops being an increase in output in an amplifier circuit. On an oscilloscope, clipping looks like a sharp flattening of both the tops and the bottoms of the waveform being amplified. It sounds dreadful. Not just bad, you understand, but truly awful. Even so, tube clipping generally does not sound quite as bad as bipolar transistor clipping because tubes "taper-off" their conduction as they approach the limits of their power supplies, while transistors will amplify more or less linearly right up to the point where the devices "bang" against the voltage limit of their power supply rails. However, any form of clipping in a linear amplifier (of any type of signal) is something to generally be avoided.

 

An interesting experiment is to take both a tube and a transistor amplifier circuit (doesn't have to be a power amp, any simple amplifier stage will work) and hook each up, in turn, to a sine-wave generator and an oscilloscope. Set the generator at 400 Hz, and crank up the generator's output while watching the 'scope. the amps output will appear on the 'scope to continue to increase linearly with the input until the amps start to get overloaded. The tops of the tube amps' sine wave will, at some point, start to change shape. The waveform will lose it's classic sine wave shape and will start to round-off at the top and the bottom in an odd way. Eventually, if you keep cranking up the input single's amplitude the top will start to flatten. This is a tube transfer characteristic, and results in what is often called "soft-clipping". The transistor amp, OTOH, will react quite differently. Again, the output will increase linearly with the increased input amplitude until the transistors become saturated - or fully "on". At this point, the waveform tops and bottoms just flatten. They don't get any higher, the flat part at the tops and bottoms of the waveform just get wider the more you continue to increase the input amplitude. This is not good for audio, but this same characteristic makes transistors ideal as electronic switches. Take a small voltage, and apply it to the transistor's 'base' and the collector-to-emitter voltage becomes essentially the same as the power supply voltage. This ability to use a small DC current to turn-on and off a much larger DC current is a very useful function in many fields of electronics.

 

+1!

 

To me this becomes at least as important as "even order harmonics" in understanding why tube equipment can sound so good (and some SS bad). Given the choice between flattened dynamics (when you get near the top of the power capability) of tubes, and the transition into harsh dynamics that happened with most early SS designs, it was easy to pick tubes. It wasn't until the 80s with Krell, Rowland, Pass, Levinson, and a few others that SS came into its own, IMHO. Top amps today, tubed or SS can sound remarkably similar to me--unless you're talking guitar amps, where tubes still totally rule.

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Although this thread has wandered quite a bit from the original question, it has been interesting and educational. But, it does leave the original question unanswered: Why would adding a tube loop on top of whatever other solid state or tube amplification you already have make things sound "better."

Synology NAS>i7-6700/32GB/NVIDIA QUADRO P4000 Win10>Qobuz+Tidal>Roon>HQPlayer>DSD512> Fiber Switch>Ultrarendu (NAA)>Holo Audio May KTE DAC> Bryston SP3 pre>Levinson No. 432 amps>Magnepan (MG20.1x2, CCR and MMC2x6)

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Although this thread has wandered quite a bit from the original question, it has been interesting and educational. But, it does leave the original question unanswered: Why would adding a tube loop on top of whatever other solid state or tube amplification you already have make things sound "better."

 

For me, in my system, a class A triode with no feedback is the way to get "correct" tube distortion. A tube buffer, for me, in my system, would only be there to help with impedance issues between devices, not to color the sound.

 

That said, I don't know if this product improves the sound or not. Perhaps it does in which case, it should be added to the system. Perhaps it doesn't, then it should be removed from the system. Only listening to it in the system will tell that story...

 

Best,

John

Positive emotions enhance our musical experiences.

 

Synology DS213+ NAS -> Auralic Vega w/Linear Power Supply -> Auralic Vega DAC (Symposium Jr rollerball isolation) -> XLR -> Auralic Taurus Pre -> XLR -> Pass Labs XA-30.5 power amplifier (on 4" maple and 4 Stillpoints) -> Hawthorne Audio Reference K2 Speakers in MTM configuration (Symposium Jr HD rollerball isolation) and Hawthorne Audio Bass Augmentation Baffles (Symposium Jr rollerball isolation) -> Bi-amped w/ two Rythmic OB plate amps) -> Extensive Room Treatments (x2 SRL Acoustics Prime 37 diffusion plus key absorption and extensive bass trapping) and Pi Audio Uberbuss' for the front end and amplification

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A French company, Jadis, in the 1980's built a (expensive) tube amp that had more than 2% THD at half power. It was, at the time, considered one of the best sounding amplifiers on the market. So, it seems that there is distortion, and then there is distortion...

 

Are you saying that it depends upon what the meaning of the word 'is' is? :)

"Relax, it's only hi-fi. There's never been a hi-fi emergency." - Roy Hall

"Not everything that can be counted counts, and not everything that counts can be counted." - William Bruce Cameron

 

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