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Review and Measurements of DarkVoice 336SE Headphone Amp

amirm

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#1
This is a review and detailed measurements of the DarkVoice 336SE pre-amp and headphone amplifier. It is on kind loan from a member who has literally been waiting months to get it reviewed! It costs USD $310 on Amazon including free shipping. It has 42 reviews summing to 4.5 stars on Amazon so customer satisfaction must be good.

This is one beast of a headphone amplifier with a massive transformer and large chassis weighing it down:
DarkVoice 336SE OTL Tube Headphone Amplifier Review.jpg

Up to now we have tested hybrid tube headphone amplifiers that use tubes as the first stage but drive the headphones using transistors. That allows the output impedance to be as low as solid state amplifier yet give you the "benefits" of tubes, whatever they may be. In DarkVoice 336SE, the signal path is all tube. The configuration is OTL meaning Output-Transformer-Less. A tube amplifier needs to block high voltage DC from going out of the unit and also reduce the rather high output impedance of tubes. This is most often done with a transformer but in OTL designs, other methods are used. The benefit is supposed to be getting rid of nonlinearities of the transformer. The drawbacks depend on the design with the most common one being high output impedance.

The big transformer here is for the power supply. I see no safety markings on the unit. I will be opening the unit later to see how it is inside. Until then, I would make sure to not touch the chassis any more than you have to and only use one hand if possible.

Fit and finish is OK but you probably noticed the crooked power switch. The volume control is damped and a bit stiff but otherwise fine.

There are a set of RCA outputs in addition to inputs so you can use the unit as a pre-amplifier if you like.

Let's get into the measurements and see how she does.

Measurements
The owner had given me a few tubes for the first stage (6SN7). I put one in there randomly and boy, was that a mistake. There was massive amount of hum both audibly and in measurements. Indeed in measurements there were more hum than signal! So I switched to the Raytheon 6SN7 which I had from review of Schiit Saga. That reduced the hum substantially although you could start to hear it past 12:00 o'clock or so on the volume control. Dashboard measurements using RCA outs show the same:

DarkVoice 336SE OTL Tube Headphone Amplifier RCA Measurements.png


Yes, this is a total disaster as measurements go. There is really no reason for such elevated power supply hum. They reach up above the largest harmonic of the amplifier itself!

Speaking of the harmonics, they fall off close to perceptual masking so they are less audible than their numbers would indicate:



The Masking threshold on the right drops off exponential and so does the distortion components of the 336SE. So if you are going to have distortions, you want them this way.

Switching to headphone jack, performance remains more or less the same but by loading it down with my standard 600 Ohm, distortion rises substantially:

DarkVoice 336SE OTL Tube Headphone Amplifier headphone Measurements.png


Covering our basics, here is the frequency response:
DarkVoice 336SE OTL Tube Headphone Amplifier frequency response Measurements.png


Pretty good actually with just a 0.7 dB drop at 20 Hz.

Warm-up showed quick stability:
DarkVoice 336SE OTL Tube Headphone Amplifier Warm-up Measurements.png


Problem arises in impedance measurement:

DarkVoice 336SE OTL Tube Headphone Amplifier headphone output impedance Measurements.png


Best case impedance is 78 ohm from 300 Hz up. Below that there is a large increase to 163 ohm at 20 kHz. This means two things:

1) With headphones with variable impedance at low values, there will be substantial change in frequency response.

2) The output is going to drop radically with lower impedance headphones.

Speaking of power, let's measure that into 300 Ohm:
DarkVoice 336SE OTL Tube Headphone Amplifier headphone Power at 300 Ohm Measurements.png


We have plenty of power here, beating even Massdrop THX AAA 789. Reason for this is that at high impedances, power is limited by voltage. Tube amps run at high voltages easily and hence, are not limited this way. The DarkVoice 336SE delivers double the power of the THX (in single-ended mode). If we increases the output load impedance to say 600 Ohm, the Darkvoice would likely pull ahead even more.

Distortion of course is massively high, reaching up to nearly 5% at max rated power! "Good news" is that it sets in gradually and there is no sharp hockey stick as we see with many transistor amplifiers.

Situation degrades substantially at 33 ohm as we could easily predict:
DarkVoice 336SE OTL Tube Headphone Amplifier headphone Power at 33 Ohm Measurements.png


Power output is just 0.2 watts, losing massively to THX's 1.3 watts. Distortion is also sky high at 20%.

Channel matching starts OK but as the volume goes lower and lower, it loses all hope:
DarkVoice 336SE OTL Tube Headphone Amplifier headphone Channel Imbalance Measurements.png


So if the hum doesn't get you with sensitive IEMs, the channel mismatch will.

No sense in running more tests. We know the nature of this beast.

Listening Tests
Testing the subjective fidelity turned out to be more complicated than one would imagine. Due to high output impedance of the Darkvoice 336SE, the output level you get in your headphones will be highly variable. As such, matching levels with test tones and my analyzer got me close but not close enough. I had to match levels manually against the reference Massdrop THX AAA 789 which is a difficult trial and error. After much work I think I got some useful results but not as reliable as I wanted.

Let's start with easier part of this trial, namely using low impedance headphones like my Hifiman HE-400i. Power output dropped substantially. As such the THX amp would run circles around the 336SE, producing tons more power, and dynamic range. Negating that by lowering the volume on THX 789, we were greeted with severe distortion if you turned up the volume on the 336SE. Pretty unpleasant experience. I read a bunch of reviews online and it was good to see the community's consensus being the same.

What the community did recommend was high impedance headphones such as my Sennheiser HD-650. Boy, did the tables turn. I could easily outrun the the THX AAA 789 (in its single-ended mode). Because of this you could operate the 336SE at lower volumes and hence much reduced distortion. Still, push the 336SE and you were greeted with shrill highs and lack of bass. The accentuated highs did give the impression of "more space" at times and exaggerated high frequency tones on some content was a pleasant addition. Once my ears tuned into them though (through careful AB test with the THX), it became a small annoyance. With a reference to test against, if you are coming from a lower output (or no) headphone amplifier, you are going to find the 336SE a revelation. It has enough power to do justice with high impedance headphones.

I then tested the two amps with my Sony MDRV6 which I think is rated at 60 ohms (?). Here, hum from the 336SE was audible when music was paused, or at times during very quiet parts. The issue was loss of resolution and impact in bass frequencies. That sense of "hi-fi" that makes you feel every note was gone with the 336SE.

Switching to my sensitive AKG AK60 headphones exaggerated the situation with the Sony above. Bass impact was gone and highs become more shrill/hissy.

The lesson here is that what you hear will be highly load, volume and content dependent. It will also depend on your hearing acuity as to whether you can hear small distortions and true resolution.

Conclusions
From objective point of, the DarkVoice 336SE is absolutely horrible. It is worse than it should be but at $310 for all that you get, I guess that is to be expected.

People though get such products for their subjective qualities. There, I can confirm the appeal of using the 336SE with high impedance headphones of 300 ohm and higher. There is copious amount of power here, and what distortion there is, is masked for the most part. In my experience of either power amplifiers or headphone, how much power you have available determines fidelity first and foremost. Lack of power results in anemic sound which seems to lack impact, and even resolution. The high output voltage of DarkVoice 336SE gives it such a strong advantage that it can override its much higher distortion. With that distortion following perceptual masking, it is not as much of a detriment as it may seem at first.

Going to lower impedance headphones is unwise though. There is insufficient current to drive them together with large output impedance which substantially degrades/changes the frequency response of the headphone. You are much better off with a powerful and distortion-free solid state headphone amplifier such as JDS Labs Atom and Massdrop THX AAA 789. They will get louder and will be cleaner to boot.

So do I recommend the DarkVoice 336SE under any conditions and lose my objectivist license with it??? :) With high impedance headphones if you like what comes with tubes as far as maintenance, and can be blind to any safety issues here, sure, you can get the 336SE and I won't be there to hound you. Use it in other scenarios and you and I will have words! :)

------------
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#2
Thank you for this review. My headphone journey started about 15 years ago, though I don't currently own this amp, I know it very well. Both your objective and subjective parts mirrors my experience with these types of otl headphone tube amps. Many years ago, this was the amp to get for newbies with high impedance headphones. As good as it can be with 300 ohm sennheisers, it was much better with the 600 ohm beyers and could be a match made in heaven subjectively. I have since moved on from these types of headphone amplifiers, but do have fond memories of how much fun it was playing around with them....of course provided you had the appropriate headphones. With lower impedance headphones, the word horrible just would do it much justice :)
 

ripvw

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#3
the only tube headphone amplifier that I would have any interest in:

https://quicksilveraudio.com/products/headphone-amplifier/

notice the output impedance at 2.2 ohms...

Mike Sanders has been making tube products at Quicksilver since 1981. He is a measurement guy and his products have always tested well with JA at Stereophile. In addition, all his designs use point-to-point wiring and Quicksilver designs have become legendary for their reliability and longevity. At $995 I can't afford it but perhaps one of our other members will find it interesting.
 

vitalii427

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#4
the only tube headphone amplifier that I would have any interest in:

https://quicksilveraudio.com/products/headphone-amplifier/

notice the output impedance at 2.2 ohms...

Mike Sanders has been making tube products at Quicksilver since 1981. He is a measurement guy and his products have always tested well with JA at Stereophile. In addition, all his designs use point-to-point wiring and Quicksilver designs have become legendary for their reliability and longevity. At $995 I can't afford it but perhaps one of our other members will find it interesting.
I have Cayin HA-1A MK2 about the same price, but hardly the same quality. I definitely hear the hum.
 

graz_lag

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#6
Compared to it's prototype, the current version looks & performs extremely well

DarkVoice 336SE prototype.jpg
 

Blumlein 88

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#8
If not for the hum, it might make a good tube preamp with some adapters. Get that SE-OTL sound in your rig by feeding it into a SS amp. This thing likely has a really simple PS, surely a little DIY magic could tame the hum.
 

Dogen

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#9
Thanks Amir, I own and enjoy the DarkVoice, and I thought your review was very accurate and even-handed.

In some ways the DV is a real pain - about half the 6SN7 types I try give very high levels of hum, even with the volume all the way down! The gain available on this amp is ridiculous; I can’t turn it up more than a quarter of the way. It’s hot. You could fry an egg on it after an hour or two.

But, with my high-impedance Sennheiser 6xx headphones, there is something about the sound quality that’s very attractive to me. Whether it’s the harmonic distortion patterns or any frequency aberrations, the music sounds very much alive and immediate. When I first got my Sennheisers, I was a little disappointed - they sounded a little bland and reserved. The DV has completely addressed all my subjective gripes with them.

This is a science forum, and I’m completely on board with good engineering, reliability, safety and rationality. The DV offers none of that. It’s a ludicrous product. But I’ve enjoyed few audio purchases lately as much as the DV, in the sense that I’m listening to more music, not just through the DarkVoice, and better appreciating it.

It’s like that bad relationship we’ve all had at one time or another. You don’t get fidelity or reliability or reason, and you never know when it’s going to blow up. But when it’s good...
 

Jimster480

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#11
Ouch! I listened to one of these before and wasn't impressed at all.
It sounded quite muddy even with my planars...
 

Jimster480

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#12
Thanks Amir, I own and enjoy the DarkVoice, and I thought your review was very accurate and even-handed.

In some ways the DV is a real pain - about half the 6SN7 types I try give very high levels of hum, even with the volume all the way down! The gain available on this amp is ridiculous; I can’t turn it up more than a quarter of the way. It’s hot. You could fry an egg on it after an hour or two.

But, with my high-impedance Sennheiser 6xx headphones, there is something about the sound quality that’s very attractive to me. Whether it’s the harmonic distortion patterns or any frequency aberrations, the music sounds very much alive and immediate. When I first got my Sennheisers, I was a little disappointed - they sounded a little bland and reserved. The DV has completely addressed all my subjective gripes with them.

This is a science forum, and I’m completely on board with good engineering, reliability, safety and rationality. The DV offers none of that. It’s a ludicrous product. But I’ve enjoyed few audio purchases lately as much as the DV, in the sense that I’m listening to more music, not just through the DarkVoice, and better appreciating it.

It’s like that bad relationship we’ve all had at one time or another. You don’t get fidelity or reliability or reason, and you never know when it’s going to blow up. But when it’s good...
What other amps do you have, just for a point of reference?
 

Dogen

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#13
My other headphone amp is an inexpensive Topping D3. I only started with headphones a few months ago, so my experience is limited. My home system is a an Oppo player, pretty nice Marantz AV receiver (don’t recall the model) with Spendor 2/3 speakers and Spendor center channel, and sometimes I’ll hook the Spendors to a Conrad Johndon PV1 preamp or Assemblage SET 300b or an ST-70 type amp.
 
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#14
Ouch! I listened to one of these before and wasn't impressed at all.
It sounded quite muddy even with my planars...
This amp is definitely not for planars. So yes, with any of those it will sound pretty bad. The 300 ohms senns and especially 600 ohm beyers can be a pretty enjoyable experience. In my experience with this amp, the higher the impedance the headphones have, the less the hum. The hum is pretty much non existent with 600 ohm beyers and the 600 ohm vintage akg 240(aka sextetts).

And to add, when this amp came on the scene many, many years ago, 300 ohm and higher headphones pretty much dominated the scene. That's not the case now.
 
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Jimster480

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#15
This amp is definitely not for planars. So yes, with any of those it will sound pretty bad. The 300 ohms senns and especially 600 ohm beyers can be a pretty enjoyable experience. In my experience with this amp, the higher the impedance the headphones have, the less the hum. The hum is pretty much non existent with 600 ohm beyers and the 600 ohm vintage akg 240(aka sextetts).

And to add, when this amp came on the scene many, many years ago, 300 ohm and higher headphones pretty much dominated the scene. That's not the case now.
Sounds like it is about 10 years old... while things have changed in the last 10 years I'm not entirely sure that the market was "dominated" by 300 ohm headphones 10 years ago...
 

atarione

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#16
I just joined after stumbling on this review.. I actually am listening to my DV336SE now, I've had this amp for 2yrs~.

Things started out ok for me with the amp, I use it mainly with beyerdynamic DT880 250ohms headphones, after about 2~mos (so past amazon return window) this amp started dropping the right channel... eventually while exercising care as to not electrocute myself I tracked down a bad connection to the headphone socket.. which I fixed.. since then the amp has worked fine.

I see you have equipment / skills to measure various things that I certainly do not.. but running mine with RCA 6SN7GT and RCA 6AS7G I hear zero hum, could be my hearing stinks? but only time I heard hum was when I first got the amp tried and old soviet tube ..and I guess as I recall when I first started using the RCA 6SN7GT it was NOS and there was a bit of hum for a little while until it burned in or ??

For what it is worth (and I suppose since it is mine..that is a good deal) I like it .. It saved the DT880's for me, because they are too bright with any Solid state amps I have.. and the highs are tamed significantly with the DV336SE.

Other gear I have and can compare my own DV to FiiO E07K/E09K , and a number of vintage receivers / pre amps :: Sony TA-N77ESD , Kenwood KR-V106R and Pioneer SX-3600. Comparing the DV to these other devices I find the DV pleasing to my own ears with my own setup.

The QC is doggy apparently based on the failure of the right channel requiring repair after 2~mos... happily I didn't die while attempting the repair (as you can probably deduce ??). I have touched the DV while it is powered on.. so far also haven't died very much at all really.
 
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#18
The Quicksilver It's a nice amp, has better than average specs and price is cheap if it uses good output transformers.

I'm also interested in the upcoming Quad PA-One+, MSRP is 1299 dollars and has balanced input and output, Innerfidelity has a review/prototype unit, howewer I don't think they'll measure it:

https://www.innerfidelity.com/content/quad-pa-one-headphone-amplifier-and-preamplifier-sneak-peek

Judging by looks alone it's quite nice.

the only tube headphone amplifier that I would have any interest in:

https://quicksilveraudio.com/products/headphone-amplifier/

notice the output impedance at 2.2 ohms...

Mike Sanders has been making tube products at Quicksilver since 1981. He is a measurement guy and his products have always tested well with JA at Stereophile. In addition, all his designs use point-to-point wiring and Quicksilver designs have become legendary for their reliability and longevity. At $995 I can't afford it but perhaps one of our other members will find it interesting.
 

gvl

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#19
If not for the hum, it might make a good tube preamp with some adapters. Get that SE-OTL sound in your rig by feeding it into a SS amp. This thing likely has a really simple PS, surely a little DIY magic could tame the hum.
I had one and used it as a preamp for some time. In the end I was disappointed, it robbed of too much of details at both ends of frequency range.
 

VintageFlanker

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#20
No safety certifications, terrible measurements. These are the kinds of reviews that make me love this site - fun to expose some products like this. Can't wait to see the teardown of how they put this thing together
Hello and welcome @metal571 ,
Good to have you here. Would be glad to also see others big YT guys around (like DMS mentioning ASR in his Atom review). :)
 
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