Katz's Corner Episode 21: How Insensitive! Part 2

The Listening...or...Rumble in the Jungle
As you may recall, in Episode 20, I proposed that headphone amplifier's output levels and headphone sensitivities should all be reported in dBu. dBu enables any consumer to quickly predict the SPL of various headphones with the various amplifiers, without needing to use algebra or logarithms. They can simply add or subtract to arrive at a basic assessment of the output level (drive) capability of the amplifier matched with the headphone and the potential impact of amplifier noise.

So today we'll pick up on this principle and briefly compare the sound qualities of six very different headphone amplifiers, concentrating on their headroom, impact, perceived loudness, detail, and depth. Then, in the next episode, I'll try to make sense of the listening and see if there is any correlation between what we measure and what we hear. Don't expect a miracle—listening versus measurements is an ongoing debate, but in Episode 22 I promise to reveal some tantalizing clues!


Fig. 1. Amplifier Jungle. From left to right, top row: JDS Labs O2, Audeze Deckard, Mjolnir KGSS Carbon HV. Middle row: AMB M3 (Katz custom build), Mjolnir Pure Bipolar. Bottom Left: Prism Callia DAC/Amp.

My headphone amplifier jungle is currently packed with six pieces: The JDS Labs O2, an inexpensive contender, using integrated circuit topology, powered by a wall wart. Next, the Audeze Deckard, a high-end DAC integrated with a high-powered discrete Class A amplifier. It also makes a wonderful standalone headphone amplifier with available RCA line inputs. I currently am not using the Deckard's DAC and I feed a separate DAC to all the amplifiers. Next, the Mjolnir Audio KGSS HV Carbon, feeding the Stax SR-007 Mk2 electrostatic headphones. This amplifier is discrete, fully-balanced input to output, using SiC FET (silicon carbide field effect transistors) output devices that Mjolnir claims are as close to triodes as solid-state can get.

Next row, left, the AMB M3 amplifier, unbalanced in and out, custom-built by yours truly using selected parts and the highest voltage AMB discrete power supply. In this M3 I've installed a specially-biased Burr Brown OPA-627 input opamp which feeds its MOSFET output transistors. Next, the Mjolnir Pure Bipolar amplifier, also fully balanced and symmetrical from input to output, biased in Class A. Last but not least, the Prism Callia DAC, which includes a built-in headphone amplifier. The Prism is a high-precision audiophile DAC that supports multiple sample rates including DSD, with both SPDIF and USB inputs. I am not familiar with the topology of its build in headphone amplifier, but we can listen to it and in the next episode measure its basic performance.

In this listening comparison, I'm concentrating on headroom and impact, and secondarily, any obvious differences in reproduced depth, separation and tonality of each amplifier. I cannot possibly do a thorough review of six amplifiers in such a short time: this is meant to be a refresher, and besides, I've given detailed reviews of several of these amps in past episodes. If you believe that all amplifiers sound the same because blind tests have not been able to reveal sonic differences, then stop reading right now, because this is not a blind test. It's as formal and controlled a sighted listening test as I know how to do, using a single musical reference that I know intimately.

First, I matched the voltage levels of each amplifier to less than 0.1 dB, if possible, with a 110 ohm resistive load. The volume control of one of the amps, the O2, was not precise enough to maintain 0.1 dB channel match at the desired gain, and it ended up correct on one channel and about 0.2 dB off on the other. Even an 0.1 dB level difference can present apparent sonic differences. The only exception to the measured level match was the Stax amp, which I had to adjust by ear, because it uses a completely different voltage system. Switching the LCD-4s between the balanced and unbalanced amplifiers is a job that takes about a minute to exchange headphone cables, so this is definitely not an instant A/B comparison.

I left all the analog controls in their matched gains, and adjusted overall volume with the 64-bit precision digital volume control in Acourate Convolver, which is dithered to 24 bits on the way to the DAC. I listened to the music at a level of about 83 dB on fortes, which is loud but not overbearing. At this level it's easy to judge the impact and strength of this rhythmic jazz piece and the potential of each amplifier to deliver this impact. For dynamic headphones I chose the Audeze LCD-4, and for electrostatic the Omega Mk2, formally called the SR-007 Mk2. Each headphone received its Katz custom EQ within Acourate Convolver. To keep the loading on the Callia very high impedance, I fed a maximum of two unbalanced amps in parallel at any time from its unbalanced outputs, and two balanced amps in parallel from its balanced outputs. So sometimes I had to move input cables to feed a different amplifier.

Listening: AMB M3
The music is by Lindsey Webster, from her smooth jazz album "Back To Your Heart", which was a Billboard top single. I'm intimately familiar with recording, which I mastered, so it makes an excellent reference. I'm playing the 24/96 master.

Starting with the AMB, I notice Lindsey's voice is clear, moderately warm, but on the dry side compared with my reference loudspeakers. The bass instrument is tight, but not very fat, and I believe it should sound fatter based on the reference loudspeakers and how I mastered this recording. There's good depth in the sonic picture: the AMB has definitely got some three-dimensionality, with the sound extending beyond the headphones developing an image outside the left and right ears, creating a virtual stage that's wider than my head. The high frequencies are a bit etched, making the sound a bit on the bright side. The snare has good, strong impact and there is no impression that the amplifier is running out of steam, so the dynamics are definitely moving and the overall sound is punchy. Detail is clear, revealing. I brought this amplifier and the Prism DAC to Tyll's Big Sound shootout in Boseman, and it wiped out all but one of the commercial contenders.

Listening: JDS Labs O2
I haven't listened to the O2 amp in about a year, so this amounts to a new get-acquainted opportunity. Switching to the O2, I immediately notice the sound is thicker, a bit mushy, but this results in a warmer tonality for Lindsey's voice that I do prefer. The O2 gives her voice apparently more body, but maybe that is just due to the overall mushy feeling. The overall sonic detail is a bit obscured compared to the AMB. The snare drum does not have nearly as much snap on the O2, but most obvious, there is a loss of depth, which has become seriously constricted.

Every instrument and vocal has moved forward, creating a planar picture instead of a curved one. I know that the sonic picture is supposed to be curved with the instruments, background vocals, and ambience forming a dimensional U shape and her voice centered and up front. I helped create that sound during the mastering, and I know the tools mixing engineer Mark Gray used to help create that image during the mixing. Although this is a multi-miked recording, many of the instruments were recorded with stereo miking, and many of the mixing tools which were used create a believable acoustic space. While we can't expect headphones to have the big, deep soundstage that speakers can produce, I do believe that circumaural headphones can reproduce a great deal of depth if given the opportunity.

With the O2, I feel the sticks on the cymbals have lost some of their attack. Overall this is not a very detailed amplifier, dynamics seem a bit constricted. Yes, it can play just as loudly as the AMB, but its microdynamics on peaks sound constricted to me. Is this due to clipping, or is it something else? In summary, this amp sounds much too forward, flat, unidimensional. Everything is in your face, there's little or no differentiation between the depth and distance of the vocals and instruments.

Listening: Audeze Deckard
Switching to the Deckard from the O2, I immediately notice the return of three-dimensionality. On the Deckard, the snare has more impact and snap and far more impacting microdynamics than the previous two amps. Lindsey's micromovements, her crescendi and decrescendi, are more obvious...and entertaining. Tonally in the lower midrange and bottom, the Deckard is more similar to the O2 than the AMB; it is warmer than the AMB, but it doesn't have the mud or loss of detail in the lower midrange and bottom compared with the O2.

In the upper midrange and top the Deckard is more detailed without sounding fatiguing. Once again I can feel the sticks on the cymbals, but without the harshness that I noticed in the AMB. The Deckard's dimensionality is moderate, perhaps a little less than the AMB, but not significantly. The overall tonality of the Deckard's sound is far more musical and 3-D than it was with the O2. There's more solidity and the sound is more lively than it was with either of the predecessors.

Listening: Prism Callia Integrated Headphone Amp
Switching to the headphone amp integrated in the Callia DAC, suddenly, the sound has shrunk, it's much smaller than with any of the three predecessors. Sadly, the overall sound quality is a pastiche of this music. This is not a high-quality headphone amp and I feel should only be used for a quick reference if nothing else is available. Yes, it can deliver the level that the LCD-4s need, but it doesn't have the separation, depth or definition. It's also bright on the high end, perhaps because the other ranges are so muddy. The sound of this headphone amp belies the incredible high quality of the Prism DAC itself, so Callia buyers should consider its headphone amp an included bonus, not an essential reference piece.

Listening: Mjolnir Pure Bipolar
Now I switch to the balanced headphone cable to audition the Mjolnir Pure Bipolar. First impression: This amp kicks ass! The bass has strength and solidity, is fat yet defined, resembling the loudspeaker sound far more than any of the previous amps. The Mjolnir's extreme high end seems slightly muted, but perhaps that is most accurate to the source. I will need to do a detailed check against the speakers when the opportunity arises. Keep in mind that I tuned my LCD-4 EQ using the Bipolar so this is definitely a biased review!

In the Mjolnir, Lindsey's voice is simultaneously warm and clear and the instruments and background vocals form a beautiful 3D image with a flowing continuity between the sides and front. This amp has a continuous, holographic wrap-around quality; none of the previous amps came close to producing this quality of image depth. The Bipolar is the sweetest sounding, clearest, most 3D, impacting and tactile dynamic headphone amp in my collection.

Listening: Mjolnir KGSS Carbon HV
Now I switch to the Stax and the custom EQ that I developed for them. This amp also kicks ass! There is a strong family resemblance between the two Mjolnirs despite having two different headphone models and despite the fact that the dynamic amp is bipolar and the electrostatic amp uses SiC FET devices. Like first cousins and friends for life, the Stax and the LCD-4, equalized and driven by their respective premium amplifiers, sound very comparable. It's effortless to switch between these two phones. There are clear tonal differences, but they are so close that I can quickly accommodate until the differences vanish in the pleasure of the listening.

The Stax is a bit more extended and detailed in the high end than the LCD-4 and I can hear the harmonics of the sticks on the cymbals better, but thanks to the EQ and the KGSS, the ugly part of the Stax rise has been completely tamed. I can finally say that cymbals sound sweet and not overbright with an electrostatic headphone! That was Mjolnir's sonic intent and I can decidedly say that they have achieved it. Maybe I could get the dynamics and stats sounding even closer with a lot of EQ effort, but I've definitely reached diminishing returns. Let's quit bellyaching about the small differences and just enjoy what I think are the two best headphone presentations on the planet. Perhaps due to the slightly forward high end above 10 kHz, the Stax seem to have a little less depth than the LCD-4 and so I give the LCD-4/Mjolnir combination a few more points because of the three dimensionality.

Prism Callia Headphone amp: C.
JDS O2: B-.
AMB M3: B+.
Audeze Deckard: A-.
Mjolnir KGSS Carbon HV: A+.
Mjolnir Pure Bipolar: A++. Prism Callia DAC: A++.

I think the amp with the best price-performance ratio, actually a bargain, is the Deckard, especially because of its built-in DAC, if this unit is still available from Audeze (currently out of stock).

The next price-performance contender is the Mjolnir Pure Bipolar, I believe a superb buy at $2100. The Mjolnir Stax amp, however, is extremely expensive at $4600 and hard to justify unless you're a crazy electrostatic fanatic like me. Just five of those and I'd pay off my Mazda Miata! Comparatively the O2 is a steal at $129 since it is very clean and powerful, if you don't mind a very forward and only moderately dynamic sound. Another bonus is the O2 is compact and light, it can drive any dynamic headphone as loud as you need, and runs on rechargeable internal batteries.

Notes on "Balanced"
You've probably heard this before, but it bears repeating: There is no such thing as a balanced headphone, because a headphone is not an active device, it has no innate reference to ground. A better term for this type circuit would be "symmetrical push-pull". I am agnostic about balanced versus unbalanced headphone amps. If an amplifier can deliver the sonics at the required levels, then it should not matter if it's balanced or unbalanced. A balanced amp can produce 6 dB more level with the same power supply as the unbalanced. But the unbalanced amp's designer can use a larger power supply and achieve equal level. Sure, it's nice to say that an amp like the Mjolnir is fully symmetrical from input to output, but does that translate to a sonic advantage or just an engineering goal? I would never dare to claim an amplifier's sonic superiority is due to its balanced topology. The variables cannot be isolated.

We can pick design nits, but at the end of the day it's how well the designer implemented his particular topology, as all things are never equal. I look forward to shooting out the balanced Mjolnir against the unbalanced Pass in the near future, because I think each amplifier represents the culmination of excellent circuit design, each one making the best of their particular topology. To facilitate quick switching, I think I'll make an adapter from male TRS to female 4-pin XLR so that I can keep the balanced cable on the LCD-4s and just move one 4-pin male connector from amplifier to amplifier.

In Episode 22, I'll take a look at the measurements and see if we can make sense of them.

tony's picture

21st.Century Tony

kais's picture

Just a reminder, Bob, as you well know the main effect of balanced signal transfer is to eliminate external influence on the signal. Fully balanced signal paths, like you find on the Stax amps takes full advantage of this by canceling out ALL foreign signals (even from devices and the cabling before the amplifier!) in the final stage, the headphone.
Therefore I would call such a headphone balanced, as I would any professional passive dynamic microphone to name a transducer on the opposite side of the signal chain.
The situation is different on amplifiers (usually for dynamic headphones) where only the output stage is balanced. The balanced topology cancels out even order distortions (k2, k4, ...) created by the stage itself, but there is not much more advantage (if this is one at all soundwise ???) because the signal level is already very high and not prone to disturbance from external.
The balanced stage delivers double the output voltage when sourced from the same power supply, but again I don't see an advantage here because the designer can easily choose a higher voltage supply for an unbalanced output stage.
This supply does not need to be stronger then (same wattage required), just the adaption is different.
Amps for electrostatic headphones are a different story because you need very high voltages to drive them (about 600V DC) and using a balanced topology greatly reduces the hazards and the efforts to avoid them coming from that fact.

Finally, balanced or unbalanced is only one of a 100 decisions designer has to make for building a great amp, and it's not the main one.

Bob Katz's picture

Thanks for your comments, kais. I measured something interesting when I compared the fully-balanced (or push pull as I prefer to say) Mjolnir Stax amp versus the Mjolnir Pure Bipolar dynamic amp. But you'll have to wait till the next episode to find out the puzzling thing that I measured.

As you know, the Audeze Planar magnetics are also physically fully symmetrical push pull. I think it's an academic argument whether one side of that push pull is commoned and comes from an unbalanced TRS plug or both sides are at equal potential to ground and come from two pins of a 4 pin XLR. All other things being equal, it probably could be argued that the fully-symmetrical drive might perform better, but given that it is the symmetrical physical design of the Audeze that cancels out the 2nd harmonic distortion, it seems to me that it should perform equally well from an unbalanced amp as from a balanced one. And since all other things are never equal, and you point that out as well, I bet you that a really well-made unbalanced amp of equal output level capability should perform sonically as well as a really-well-made balanced amp. The holistic skills of the two designers to do the best they can with each topology should top out any last "balanced" versus "unbalanced" arguments.

Sort of reminds me of the top chef contests on the cooking channel. I wouldn't disparage any of those incredible chefs. Nor would I disparage any great designer just because they prefer to use one topology over another.

One dubious technology I question is the wisdom of AMB's choice of using an active ground (more correctly "active driven floating common connection" in the M3. I measure considerably more ground-related hum spikes in this amp than I do with competing unbalanced output amplifiers. Are they audible, though? No.... the spikes are well below the threshold of audibility. There is no audible hum in this amp. Do the hum spikes interact with the audio signal and cause some of the edge that I hear? Well, perhaps we may learn the answer with far more sophisticated analysis and testing than I am capable of doing.

Bob Katz's picture

You are correct, kais, that the main purpose of balanced input is to cancel out foreign signals from influence. As long as the DAC or signal source and the power amplifier are powered from the same outlet and physically located next to one another. And the power line has a clean ground and the power inlet design of each amplifier is well-done.... the chances are slim to none that any common mode hum or RFI would be picked up by the unbalanced amp that could be cancelled by the balanced amp. Balanced connections were designed to help when preamplifier and amplifier are separated by a distance and/or powered from different power and/or when there is a ground loop between them. Not relevant for the majority of consumer situations, including mine.

kais's picture

In fact EVERY unbalanced analog interconnection of mains powered devices produces some amount of hum, be it obviously audible or not. Even worse if both devices use safety ground (3 prong plug).
The amount is depending on device and cable placement.

Bob Katz's picture

some amount of hum. It is totally possible to have a completely (measurable) hum-free unbalanced inter-connection. It's just harder, but not impossible!

Bob Katz's picture

...cause any kind of hum issue. If the power system is properly designed, and the device (e.g. D to A converter) is properly designed you can have line powered gear which is grounded to the U-ground with ZERO ground loop or hum problems and ZERO measured hum in a detailed spectrum analysis of the output of the DAC or headphone ampliifier. Read Muncy's articles in the special issue of the AES journal on power and grounding to understand the design criteria for that to happen.

My power system in my listening room and machine room has been specifically re-built by me. All outlets are hospital grade isolated ground (that's part of the key), all grounds are home run to a central breaker box in the listeniing room. All devices that employ a u-ground are audibly hum free and a great deal of them are also measurably hum, RFI and EMI free. It's not magic, it's science, once you pay attention to issues of loop area. Lifting the U-ground on a device that has a three pin plug is not only unsafe, and against code, it is absolutely not necessary if the manufacturer of the device follows proper internal grounding practice (Muncy describes the proper practice) and if the power and grounding system is all home run to a central point in the room.

kais's picture

As you describe it, a lot of effort is necessary to make unbalanced equipment quasi hum free.
I know what you are talking about, I have "dehummed" several of my colleagues studios during my career.
I guess the average user does not have the options to do so.
Properly built balanced equipment does not need this effort.
Imagine a life stage situation where all the microphones are unbalanced- impossible!
I vote for balanced whenever possible.

xnor's picture

about balanced, unbalanced and symmetric signals/lines.

Balanced just means matched impedances. So equal impedances in the driver, line and receiver. That's it.
That's what gets you rejection of external noise.

Unbalanced means unequal impedances.

Then there's the signal. Whether it is asymmetric or symmetric is irrelevant to whether a circuit is balanced or unbalanced.

Finally, there are well-known terms to describe the configuration of amplifiers that single loads such as speakers or headphones:
bridged and parallel.

Bridged is simply one non-inverting and an inverting amp connected o a single speaker. That theoretically doubles the output voltage, but also doubles the damping factor.

Paralleled is just two or more amps in parallel driving the speaker. Both can of course be combined.

xnor's picture

*halves* the damping factor of course.

kais's picture

Balanced = symetrical:
Sender: uses 2 wires, one in phase (+), 2nd with inverted phase signal(-): 1, -1
Receiver: sums the signal from the 2 wires above, but receiver inverts phase on 2nd wire (-), so signal is back to (+) , = normal again:
+1 -(-1) = 1+1 = 2
As external noise is same on both wires, hum and noise is canceled out at the receiver:
(+ noise) - (+ noise) = 0; no noise!

This even works without extra screening the two wires, like in telephone lines!
Balanced lines are not related to ground so any ground potential difference between devices has no influence on the signal. Only this way you can transport audio across the country on analog lines.

Bridged amplifier do basically the same as sender, but the purpose is different, it's just to double the voltage.

A headphone is principally a balanced receiver, except if the minus wires of left and right channel are connected together (for common ground), like in cables with TRS plugs.

There are three types of balanced connections: transformer balanced, electronically balanced and quasi-symetric (semi-balanced). Their basic concept is the same, they are choosen depending on the purpose and price point.
Single sided = unbalanced:
One wire is for signal transfer, a screening tries to protects from external stray noise and unfortunately has to serve as ground reference for the audio at the same time. It cannot do this perfectly, as it's never absolutely zero ohms.
So every difference in the ground potential between two devices (usually in form of hum) is only partly eliminated by the grounding/screening and becomes part of the audio .
Matched impedance:
Sender and receiver and the cable have the same impedance, expressed in ohms. This is only necessary in networks (be it analog or digital), where the line length is longer then the wavelength. In that case, if the matching is not perfect, you get reflections.
You can hear this in older long distance analog telephone lines if they are not matched properly you can hear the echoes.

xnor's picture

I'm sorry but that is simply incorrect.

1) Balanced is not symmetrical. Those are entirely different things.

2) To get the same noise on both wires you need matched impedances. The signal is irrelevant. Think about it ..
(2V + noise) - (0V + noise) = 2V without noise
That is what balanced is. Matched impedances ensures that interference induced in the line is common-mode and therefore rejected.

You confuse a lot of concepts again. Finally you bring in another concept and say that "single sided = unbalanced."

Before we go there let's make it clear AGAIN that there is balanced and unbalanced circuits and lines.
Secondly, we have asymmetric and symmetric signals. That's a separate thing.
A balanced circuit or line can carry an asymmetric signal perfectly fine. That doesn't make it unbalanced.

Now to your "single sided = unbalanced" comment:
First of all it's called single-ended. Secondly, you're just adding to the confusion.
Single-ended signaling is contrasted with differential signaling.

Differential signaling is basically just transmitting a signal as a differential pair of signals through two wires (typically twisted pair) or two traces on a pcb.
Single-ended means transmitting the signal through one wire and ground.

MRC01's picture

In audio, "balanced" is differential, and symmetric.
Balanced is differential because each wire carries a signal (neither is ground), and the musical waveform is the difference between the signal in each of the 2 wires.
It's symmetric because at any given instant in time, the signal voltage in one wire is the reverse polarity of the other. Their sum is always zero, their difference is the musical signal.
This is opposed to "unbalanced", where one wire carries the entire musical signal, and the other wire is ground -- it has no signal.
Either way, the musical signal is the difference between the 2 wires. The speaker or headphone responds accordingly not knowing or caring whether both wires carry a signal, or one of them is ground.

Zeleni Zec's picture

From your words: one wire carries the entire musical signal, and the other wire is ground -- it has no signal, it is clear that you don't understand anything about signals and electronics in general. If you try to put signal through one wire you would very soon come to conclusion that something is missing because your signal is not coming through. Every signal needs return path, usually ground if it is connection between two devices in question. That is same in balanced connections as well, they need return path - ground. If you open any balanced cable you will see three wires: two wires carrying + and - signal referred to the ground - third wire.

xnor's picture

> "From your words: one wire carries the entire musical signal"
But here are my actual words: "Single-ended means transmitting the signal through one wire and ground."

And also besides being utterly dishonest please stop projecting your own ignorance on others.

Zeleni Zec's picture


infidelity-scotty's picture

As I understand it a single ended signal is a voltage wiggle on the input ("signal") wire and there is no voltage on the ground ("return") wire.
Obviously not completely true as the return wire has inherrant resistivity (etc) and will therefor bear a voltage sufficient to "push" the current through it.
Bear Skat? You explain.
Kind regards

MRC01's picture

Connect two scopes, one to each of the 2 wires of an unbalanced audio signal while it's playing music. One will show the musical signal, the other will show a flat line.

Do the same with balanced audio and each scope will show a signal, they will be mirror images -- one will be reverse polarity of the other. The 3rd wire (if there is one, there won't be if it's a balanced connection to a headphone or speaker) will show a flat line.

xnor's picture

Sorry, but I can't help you if you neither want to read nor understand but instead prefer to stubbornly stick to your mistaken opinion.

xnor's picture

> "In audio, "balanced" is differential, and symmetric."
I'm sorry to have to do this again but no, it isn't.
Balanced audio means interconnecting audio components through balanced lines. Again: this means equal impedances.

Differential mode isn't required. Granted, balanced audio connections very often use differential mode, but it's not required for balanced operation (audio or not) at all.

zobel's picture

...except for microphone cable runs, and there always.

I live in a two wire house. I've only run into audible hum after introducing a third ground for an audio system. I have a detector that buzzes when held next to grounded circuits that are reversed on the mains. It served it's purpose once in finding a culprit. I have a system that is totally battery powered, (19.5 Volt amp, battery powered sources)...not balanced though...no hum to hear there either, no real difference. If you can't hear it, it doesn't matter.
Most designs , by far, of amplifiers, and electronics in general are unbalanced, and noise is generally designed out, for all practical purposes.

mariscosyketchup's picture

Spritzer (Mjolnir Audio) rocks!
Thanks for the article Bob, it was a nice reading.

MRC01's picture

Well engineered solid state amps have measurements showing noise and distortion below human thresholds of hearing. Yet we can still hear differences in level matched double blind tests. That difference must be real, so as an engineer, I believe there must be some way to measure it. This suggests (A) there are different kids of measurements we should be doing; or (B) different ways of making the measurements we are already doing, that better represent performance under actual listening conditions.
Any ideas exactly what we can do differently for (A) and (B), so measurements correspond better to audible differences?

xnor's picture

Please show us a properly executed DBT where differences were heard but no significant differences between the amps could be measured.

Core's picture

Please do not ask MRC01 to stand on his head and do back flips. Because if measurements of ANY two amplifiers predict that no one will be able to hear a difference in a double-blind test, no one has been able to hear a difference in a double-blind test.

Pokemonn's picture

You may not stack those metallic amps on metallic amps. It may sound metallic and harsh and too bright.
I tried to put my stax setup on my kitchens very soft Vinyl made surface floor. then my Stax SR-009 sounded unlisnable level darkness. Seriously please try it if you have very soft surfaced floor in your home.

Pokemonn's picture

If you dont have very soft surface floor, you can use bed and/or sofa for it experiments.

Pokemonn's picture

Those vibrating power transformered amps' vibrations colored sounds ime.
even my $6000MSRP Luxman headphone amp sounds screecy when it put on metal wired rack.

Martin.'s picture

Would love to see you, or someone on Innerfidelity, review the deckard. You mentioned that it has the best price/performance ratio, especially because of the dac. Is the A- directed at the device as a whole, or just the amp part?

zobel's picture

...will help clear things up here;