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Review and Measurements of Little Labs Monotor Headphone Amp

JohnYang1997

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I see what you are saying.. Valid enough, but kind of a side point to what was actually being discussed on the previous posts. The pieces discussed were being held accountable to specific measurements by the reviewer, and the designer explained why he made certain design choices. He explained that he could have changed, or added things to the circuit to improve on those measurements, but that the diffence in those measurement disparities are inaudible, but the circuit changes needed to reach them would have degraded the sonic performance of the unit, as he is following a less is more, straight wire with gain philosophy.

He's been designing for 40 years, and knows what he's doing. He knows what he's after. The unit is praised for its natural, transparent sound. So again, using only measurement goals as the holy grail in circuit design has its shortcomings. Listening is equally important.

I read a review here on the Benchmark DAC3, which was praised for its measurements. When you talk to the peopl att Benchmark, all they talk about are measurements, and specs. That was he entire design approach apparently. It was a remarkably clean and detailed Dac, but the least musical of the ones I auditioned.
Read some more threads here. Especially the psychoacoustics and how to interpret measurements. This is audio SCIENCE forum. Everything is FACT based. Not philosophical.
 
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amirm

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For sure, different capacitors, and resisters for example may have the same values, but sound completely different.
For sure they do not unless a circuit requires a specific type of capacitor.
 
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amirm

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He's been designing for 40 years, and knows what he's doing. He knows what he's after.
No he doesn't. Designing audio gear is not the same as properly testing the sound that comes out of them. By your logic, a doctor with 40 years of experience doesn't need to conduct double blind tests to develop new drugs. Yet we know no drug is developed or approved without such bias controlled testing.

Remember, his skill is in designing electronics, not your perception of sound.

I have had that much experience and know the psychoacoustics and still, I have had catastrophic failures in detecting fidelity of systems. In more than one instance, I identified "big" differences in two sounds that were later proven to be identical. The latter is key: you need to be tested to know how good your hearing perception is. Self-grading may not apply I am afraid.
 

JazzyMark

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I feel you're not gleening the meaning of whats being said, and missing the point, and rather drumming home something that may true, but beside the point. Sure it's possible to measure almost anything. That wasnt the point to begin with.
 
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amirm

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I feel you're not gleening the meaning of whats being said, and missing the point, and rather drumming home something that may true, but beside the point. Sure it's possible to measure almost anything. That wasnt the point to begin with.
Not really. Your arguments are classic lay intuition we hear every day of the week and twice on Sunday. Please put trust in what you can verify such as measurements I provided. That this guy has experience, components matter, etc. is all unreliable, anecdotal information of little value. Don't dismiss audio science while you believe in science elsewhere....
 

JazzyMark

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Not really. Your arguments are classic lay intuition we hear every day of the week and twice on Sunday. Please put trust in what you can verify such as measurements I provided. That this guy has experience, components matter, etc. is all unreliable, anecdotal information of little value. Don't dismiss audio science while you believe in science elsewhere....
I do not dismiss science. It's invaluable. It is my assumption that a great designer of audio gear, knows the science inside out, and of course utilizes testing and measurements, which are vital in the design process, otherwise he'd be a charlatan. I would have thought my points made would not have suggested otherwise. Still one can hit all the metrics they look for in a design, and get for instance, the lowest levels of distortion in all the areas they design for, and make a piece of gear that is indeed 'clean, but may be lifeless in its portrayal of sound - not get the wood tones in a cello right for instance. Can you measure for that? I don't know, but you can listen for it. Happens all the time. Ears play a important role. Indeed there is more than enough room for error in psycho-acoustics, so listening tests should be thorough, and as fool-proof as possible. I don't feel this undermines the importance of science.
 

JohnYang1997

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I do not dismiss science. It's invaluable. It is my assumption that a great designer of audio gear, knows the science inside out, and of course utilizes testing and measurements, which are vital in the design process, otherwise he'd be a charlatan. I would have thought my points made would not have suggested otherwise. Still one can hit all the metrics they look for in a design, and get for instance, the lowest levels of distortion in all the areas they design for, and make a piece of gear that is indeed 'clean, but may be lifeless in its portrayal of sound - not get the wood tones in a cello right for instance. Can you measure for that? I don't know, but you can listen for it. Happens all the time. Ears play a important role. Indeed there is more than enough room for error in psycho-acoustics, so listening tests should be thorough, and as fool-proof as possible. I don't feel this undermines the importance of science.
Simple as this. Majority audio related products, regardless being incredibly cheap, are audibly transparent as long as the use condition falls under the condition it designed for.
This does in some way mean most audio manufacturers should go out of business. However, that doesn't make much sense. Hence they can exist but need to compete. If you sell products with premium, they gotta be more user friendly, more pretty, and has better performance.

It's not same circuit with different components sounding different but different circuits with different components can sound exactly the same.
 

solderdude

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Still one can hit all the metrics they look for in a design, and get for instance, the lowest levels of distortion in all the areas they design for, and make a piece of gear that is indeed 'clean, but may be lifeless in its portrayal of sound - not get the wood tones in a cello right for instance

The woodtones are caused by the harmonic profile and decay of the individual fundamental and harmonics.
No (competent) amplifier will do that differently.
VERY easy to test as well for this both with static tests (test tones) as well as nulling.
There are no parts that 'favour' certain music structures more so than others (also cables can not).
If they did it would be called an equalizer and its effect is very audible.
When decay would be different this too is very measurable and verifiable with null testing.
 

solderdude

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Real world load is not a pure resistance load like AP but also often has a capacitance as well. However this is “non-standard” test conditions, so they are often dismissed.

Real world load of a DAC usually is a power/headphone/control amp.
Their input resistance is purely resistive. In some cases there is a small capacitance in series with a small resistor to limit HF input garbage.
Also most DACs have output resistances below 100 Ohm, there are a few exceptions perhaps.
The input of the Monotor is purely resistive most likely.

The capacitive load on a DAC is mostly the RCA cable. Unless the cable is high capacitance and really long this isn't of any consequence within and well above the audible range.

With passive attenuators the output resistance does indeed vary but in normal listening conditions will be well below the input resistance value of the volume control.
In certain positions (volume at -6dB setting) and long or unusual high capacitance cables there can be measurable roll-off.

When real world loads have an impact on sources is when driving transducers and when digital or HF signals are not properly terminated.
 

bcgood

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The Topping L50 was scored very high at Audio Science review due to its measurements. Here are my conclusions after listening to two SACDs for the last couple of hours. Miles Davis Kind Of Blue and Steely Dan Goucho. Both headphone amps sound good. The Topping L50 sounded very detailed but maybe a little bright and flat, very quiet. In comparison the Little Labs Monotor had a nice 3D like quality to it, more depth and the detail was still there just sounded more organic and overall sound was more authoritative. So in other words the Monotor won in my subjective listening tests. I used my Sennheiser HD 650 headphones as well as my Audeze LCD-X headphones for the comparison.
 

littlelabs

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A good friend of mine brought the measurement review of the Little Labs Monotor to my attention.
I'm the designer of the Monotor.
I very much appreciate the effort Amirm put into it. It’s interesting and useful. I just hope it doesn’t discourage people from seriously listening and comparing, using their own ears as the final judge when making a headphone amp purchasing decision.

I do not dispute the accuracy of the measurements. I do however disagree strongly with the conclusions drawn by Amirm on some of the measurements. In my 40 years of working professionally designing, maintaining and manufacturing audio electronics for recording and mastering facilities, I can assure you a layman audio fanatics biggest mistake is judging a unit to purchase on specs alone.
As a designer working with professionals with serious listening chops, you over time learn what makes a circuit sound better and what specs matter, and what specs are a wank.
One can make two identical circuits with different chosen components that measure identically but can sound very different.
One can also add to a circuit to make a noise floor even quieter when the noise is already audibly imperceptible.
One can also add to a circuit to make more current available when in reality it won't be used.
Each active addition to a circuit is one step further away from the purity of the source.
My design philosophy is to use minimum active circuitry in the signal path to bring the headphone to a respectable volume and command that headphone to be as transparent to the source as is possible. There is a reason a power amplifier makes a poor headphone amp. You don't put a dragster engine in a Porsche.

Some notes:
Headphone Imbalance vs. Volume Position.
I challenge anybody out there that says they can perceive an l/R imbalance of less than 1dB. Yes, it's nice when you can find a simple analog carbon pot that tracks closer than 1dB top to bottom in the whole logarithmic scale, but if you find one that has 30 steps within 1dB you're doing great. The monotor pot is not a discrete stepped attenuator, but it tracks pretty damn well for what it is. Of course, you can use an IC based potentiometer that can track perfectly, but then you just added another active step further from transparency. Oh and regarding steps, how many more than 30 is necessary?

How much power is necessary for driving a headphone?
I am using daily both the HD600 Sennheiser 300 ohms and an Audeze LCD-X 20 ohms and both work wonderfully with the monotor, and certainly without distortion at very loud volume.
Those two phones are the two most popular used by professionals paired with the monotor.
I listen to all genres of music and not once did I notice distortion even at dangerously high volumes. Now I'm not familiar with the Hifiman HE-400i, but I'll take Amirm at his word that the monotor distorted before the HE-400i did.
But, and this is very important, the casual reader of this review would most likely overlook this. This HE-400i is a rare case, a new breed of headphone that is very low sensitivity, and also low impedance (FYI low impedance phones are typically very sensitive). I think another headphone with that spec is the Mr. Speaker Aeron (closed back), a headphone I like a lot. I have never pushed it so loud the monotor distorted, but I don't dispute that you can.

In my experience with headphone amps, voltage gain, which is necessary to drive phones to a respectable level, is far more important a spec than power output. Rarely is over 100mw of power necessary to happily drive a well-designed headphone. The Monotor has 13.8 dB of gain. I chose that gain for a perfect pairing with my most popular headphone the HD600. That gain on the HD600 gives you a great range from soft to ridiculously loud, and oh so clean... Now where that gain becomes a problem is with super sensitive phones, mostly IEMS. Some IEMS are crazy sensitive, those IEMs I do not recommend with the monotor.
The monotor is not a one size fits all, you don't use a Porsche for off-roading now, do you?
That being said I have some drummer friends that love it super loud and use the monotor on stage to power their IEMS, they couldn't be happier. I worry about their ear health.

Frequency response:
The monotor is .3 dB down at 20kHz, at 50kHz it's 1.7dB down this is on purpose. I can assure you, you cannot only not hear less than 1dB imbalance left to right you sure as hell can't hear .3 dB down at 20kHz. Amplifying stuff that's not music does not add to a sonic experience. Overlooked in this review, the monotor has an excellent low-frequency response, flat to 3Hz (where you can actually feel it).

Mono functions and other pro features and price:
The monotor found its way into audiophile circles, but it is truly a pro device.
The mono functions do add greatly to the cost of the monotor. The phase function makes checking azimuth on tape machines and phono cartridges a breeze.
The monotor remains balanced, completely differential internally through to the output driver. We don't use any balanced to unbalanced buffers.
Only a single active stage is used surrounded by top-notch passive components in a hybrid thru-hole/smt component selection. This includes Dale Vishay thru hole resistors, Nichicon Muse bipolar capacitors, polystyrene capacitors, and massive power supply reserve caps using some of the quietest voltage regulators available. None of these components add to what can be measured, but definitely bring you closer to the source sonically, and makes the unit more costly. I laugh when I hear comments of the monotor being overpriced. They wouldn't say that if they saw the BOM (bill of materials).
In closing I didn't come here to bitch, I came here to enlighten. I appreciate what Amirm has done but I want to encourage the consumer to look past the spec. Any EE can make textbook audio gear that measures well, but it takes ears and years to learn what really sounds well.
Cheers
Jonathan Little
ps
Amirm I measured the monotor output impedance to be 0.5 ohms!
@littlelabs

I mostly agree (such as being 0.3dB at 20kHz), but one statement I would like to address:



Maybe for one measurement (e.g. frequency response), but not true that a real sonic change (i.e. not one you imagine) cannot be measured. How can the flow of electricity be altered but not measurable?


I generally agree; I would like to see the Emotiva A-100 measured though, it already has pretty good power natively:
8 Ohms: 60 mW / channel 33 Ohms: 200 mW / channel 47 Ohms: 250 mW / channel 150 Ohms: 430 mW / channel 300 Ohms: 440 mW / channel 600 Ohms: 350 mW / channel

But, once you put it in "direct drive" mode, it becomes insane, they even state no liability for damaged cans:
8 Ohms: 50 watts / channel 33 Ohms: 12 watts / channel 47 Ohms: 8.5 watts / channel 150 Ohms: 2.6 watts / channel 300 Ohms: 1.3 watts / channel 600 Ohms: 0.6 watts / channel
I just saw this interview with the legendary Bernie Grundman this is only a clip.

Bernie Grundman on electronics

https://youtube.com/clip/UgkxRj21wXFe-2Nb9xHnfHn6aj3nNTmyBHGx?si=IuF1owNJRQQFtwgj
 

littlelabs

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It's always sad to see an accomplished person dribbling out nonsense.
Wow, that's rich. And who are you again, and what gear have you designed, and which albums have you mastered in the past five years? Lots of foolish know-it-alls on this forum. What Bernie said is dead on accurate. I know his tech, Beno, who designs most of Bernie's electronics; he is a wealth of knowledge with a mastering facility with some of the best ears in the business to critique his work. Bernie is the most sought-after mastering engineer for audiophile work in the business, and you say he is "dribbling out nonsense," check yourself.
 

SIY

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Wow, that's rich. And who are you again, and what gear have you designed, and which albums have you mastered in the past five years? Lots of foolish know-it-alls on this forum. What Bernie said is dead on accurate. I know his tech, Beno, who designs most of Bernie's electronics; he is a wealth of knowledge with a mastering facility with some of the best ears in the business to critique his work. Bernie is the most sought-after mastering engineer for audiophile work in the business, and you say he is "dribbling out nonsense," check yourself.
Someone who understands basic sensory science and electronics, as well as the literature on audibility. And why “argument from authority” is a serious fallacy.

As well as not being an equipment peddler.
 
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