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Darkvoice 337 - A Review

post #1 of 909
Thread Starter 

The Darkvoice 336 that some people here at Head-fi began taking orders on early last year generated tremendous interest in this Chinese headphone amp manufacturer. Its polished looks, meticulous construction and outstanding sound grabbed my attention as well. For a couple of months, I was seriously considering ordering one. Then I learned I would be returning to China for Christmas/New Years. I figured I would wait it out and do the due diligence during vacation. I looked around on this Chinese headphone site www.erji.net and found a store in my hometown on Hangzhou that sells headphones and headphone amps. It was in the information technology district (think Circuit City, CompUSA, Best Buy grouped in a couple of street blocks), perfect. It was a long wait until the end of December but my patience had its reward.

Buying the amp:

This store looked great online. It had pictures showing a huge stock of headphones and headphone amps. Yes, the Darkvoice 336 was one of them. I took down the address and went to find this store. I had a general impression it would be one of many stores in a big mall. The photos had given me this general impression. I was grossly mislead. The store was in some building numbered 402. As I walked down the street, I saw 390, then 398, then 400, and then 406. What? Something’s missing. Indeed, some building was torn down and construction on something newer was on its way. I was shocked. Could the store be gone already? It certainly is plausible. You never know with these internet stores, not to mention its specialty store status. Fortunately, I asked around for a while and eventually found a slightly run down building with a residential feel. Surely this wasn’t the place? It was; on the third floor, in what seemed like a converted apartment.

There was no big sign outside or anything. The door was closed too. There was a doorbell though, I went ahead and rang it. Some young guy opened the door. I told him I was there to examine the Darkvoice 336. He said he didn’t have any in stock at the moment. That sucks. What about the Darkvoice 337 then? Yes. He had one. Why not listen then, I thought. I had always wondered why it had dual volume controls yet not balanced output.

He went into the stock room and brought out the beast. This amp is massive. If you can imagine three Darkvoice 336s set next to each other, that is how massive this thing is. The young guy hooked it up to some Philips CD player. He even offered me a Beyer DT-880, my dynamic phone of choice. Then I noticed, I forgot to bring some CDs. He didn’t have much Western music either. He did have this mix with Hotel California, from Hell Freezes Over. I’ve heard this song on many an occasion. I gave it a shot. Wow, that kick drum in the beginning sounded real impactful and robust. I went ahead and listened for a few more minutes. He had a pair of Audio Technica ATH-A900ltds; they sounded real closed in (compared to DT-800) but what bass! I was beginning to ponder the possibility of buying this amp. I still wanted to know what the Darkvoice 336 sounded like though. I asked him when he would have it in stock, he told me about a week. That was cutting it close with my scheduled departure back to the US. Nevertheless, I decided to wait it out. There is a significant price difference and I wanted to make an informed decision.

A week passed and I gave the store a call. They still did not have the Darkvoice 336 in stock. This was bad news. Should I leave empty handed? Or should I jump on the Darkvoice 337. It sounded really really good. I decided to listen to it more extensively. I brought in some of my own CDs and auditioned it for almost an hour.

But how was I going to bring it back? I was already told it would only be in 220V too. During that hour, I made up my mind. I’ll ship it back myself and I’ll buy a voltage converter. If I let this go, I’ll never forgive myself.

About the amp:

So here it is, halfway across the globe in the US with me. When I was talking to the post office woman, she said it was guaranteed to arrive in a month. That was second most expensive option. I had reached my limit and settled on it. To my great surprise, it arrived in a week (I shipped the amp but brought the tubes along with me on the plane because they were the most sensitive to mishandling). Perfect! In fact, it came two days before my voltage converter. Those were two very agonizing days.

Here are some pictures of the outside.

This amp was designed using a Beyerdynamic DT-880 and an AKG K1000.

The internals are similar to the Darkvoice 336 and 332, very neat point to point wiring. The parts used are not name-brand. But (according to the manual) part of Darkvoice’s philosophy is making ordinary parts sounds amazing. This amp is basically a dual mono setup with two separate power supplies.

The stock tubes are NOS Chinese military tubes made by the old Shuguang tube factory, 2x6J8P and 2x6N5P. I would like to clarify that the Darkvoice 337 does not use the same tubes as the Darkvoice 336. The preamp tube in the Darkvoice 336 is equivalent to the 6SN7 a twin triode. The Darkvoice 337 preamp tubes are equivalent to the 6SJ7 pentode. Two pentodes are needed when only one twin triode is required. This also means the Darkvoice 337 is not merely two 336s combined, but a different modified setup. Pentodes are also more powerful than triodes as well. That means this amp has some serious power. Also, 6SJ7s are very plentiful and often very cheap. There is the military equivalent 5693 (RCA red hots) and also the loctal 7C7 tube. The power tube is the same as the Darkvoice 336 though.

My review setup:

Source: M-Audio Revolution 5.1 (coax)
Zhaolu 2.0C using 2x OPA2107 and 1x OPA827 (still a prototype opamp at the moment I think)

Amps: M^3
Darkvoice 336


Beyerdynamic DT-880 (’03)
AKG K1000 (borrowed)

Songs to be examined (all lossless):

The Eagles – Hell Freezes Over – Hotel California
Guns ‘N Roses – Appetite for Destruction (MFSL) – Sweet Child of Mine
Paul Simon – Graceland – Diamonds on the Soles of Her Shoes
New Order – Substance – Bizarre Love Triangle
U2 – The Joshua Tree (MFSL) – With or Without You


I do not consider myself an audiophile. I do have a great passion for music. In the end, it’s the music that really matters. I listen to most genres of music but focus more on classic rock, alternative and classical. I notice subtleties in music but often find it hard to describe differences between headphones and amps. I also don’t spend too much time only listening to music. I’m from the multitasking generation where listening to music is an accompanying task, not something to concentrate solely on. Also, this Darkvoice 337 has been on continuously for almost two weeks. It’s safe to say it is fully burned in.

How does it sound:

My general impression of the amp is that it is astonishingly powerful. My normal listening volume on the DT880s is around 9 o’clock, with the AKG K1000s it is around 12 o’clock. There is a lot of impact, especially in the bass region. Whereas the FEEL or M^3 drives with the force of a large hammer, it feels like the Darkvoice is wielding a sledgehammer. Clipping? No such thing. The sound is very warm, very musical. There is no leanness or glare to the music. The midrange and the highs are both excellent. The amp sounds smooth yet not slow either. The soundstage is incredibly wide, much more than I though possible. Finally, the detail is to die for. Nuances are never lost, subtleties are all revealed. Of course, since there are countless tube rolling options, the sound can be tuned to your own liking. More on that later.

The Eagles – Hell Freezes Over – Hotel California

This was the song that got me hooked. This was an awesome live album. You can tell they rehearsed diligently. It is true their reunion tour(s) ticket prices were exorbitant, but few bands these days are as talented as they are. Plus the CD cost less than $20.

The soundstage is naturally very wide on the K1000s. If I was given more tactile/physical feedback, I could swear I was sitting in the actual concert hall. The sound is very balanced. The bass reaches reasonably deep and the highs are well represented. I would even venture to say the bass is a bit emphasized. For those who think the AKG is bass shy, this is definitely an amp to change that opinion. The renowned AKG midrange? Don Henley has a sort of rustic, scratchy voice. The amp really brings that voice to life. I really don’t know how to describe it aside from saying what I hear on the recording is what he sends into the microphone. Also, during the guitar solo, the individual plucks on the guitar are distinct, powerful and end with a very natural decay. There’s something about electric guitar that just sounds right, sort of like the bagpipes. I don’t know what it is, but this amp really allows you to enjoy those stirring notes.

I think the DT880s share many characteristics with the AKG K1000s. Many people complain about weak bass and piercing highs but praise its incredible detail and unreal soundstage. The Darkvoice 337 compensates for the DT880’s weaknesses and augments its strengths. The bass line here reaches incredibly deep and the drums are conveyed with chilling power. A detailed bass-shy phone could very well sound boring, very analytical. This amp brings back that emotion. Most people agree a tube amp can tame the DT880’s highs and boost its bass. That is exactly what the Darkvoice does. The impact of the outputted sound reminds me of a Dynalo: punchy, dynamic. Yet the tonal balance and the musicality takes me back to the ASL MG Head OTL I used to own. In some respects, the soundstage was even more impressive than the K1000s. How is that possible? When I’m wearing the K1000s, I do not feel like I’m wearing headphones. Deep down, I’m expecting a speaker-like experience, especially since the lack of isolation give me a sense of being “out in the open”. When I’m wearing the DT880s, just by the feeling something covering my ears, I feel I am in some kind of container, isolated. In this state, when I hear something that seemingly comes from behind me or outwards from my sides, I am surprised and thrilled. Whereas the DT880s belie the headphone experience, the K1000s ultimately fall short of the speaker experience.

Guns ‘N Roses – Appetite for Destruction (MFSL) – Sweet Child of Mine

K1000s: Intro guitar riff has amazing space. But ultimately Axl Rose’s voice sounds a bit lean and lifeless. I attribute this mainly to the soundstage. It’s too wide to be intimate. He sounds like he’s somewhere far away shouting at me.

DT880: I like this song much more on these headphones. The electric guitar sounds better. The bass goes deeper. Axl sounds closer and more full of life.

Paul Simon – Graceland – Diamonds on the Soles of Her Shoes

Ladysmith Black Mambazo sounds so good here. The group’s voices sound so powerful, so reassuring, so deep. Paul Simon’s voice also sounds amazing. The inflections in his voice are extremely clear and realistic. At the point when the into singing ends and there is a brief instrumental section, the drums attack with amazing vigor and the bass guitar picks with authority and presence. This is a very exciting and upbeat song. The shear sonic impact of the Darkvoice 337 brings that extra bit of life into it. The warm tube sound rounds out everything removing any hint this is digital music.

New Order – Substance – Bizarre Love Triangle

I want to first note there are many many remixes of this song, so your results may vary. The version on this album has a lengthy and prominent section of cymbals at the beginning of the sound. This is a great display of the Darkvoice’s ability to present highs clearly and in a non-fatiguing way. The transients are also very fast and definitely keep pace with the music.

U2 – The Joshua Tree (MFSL) – With or Without You

The soundstage and the bass are tested with this song. The Darkvoice 337 definitely steps up to the challenge. The intro contains so much ambience, while the beginning bass line sounds so clear, tuneful and full of energy. Bono’s singing is also presented with aplomb. Every breath he takes, every crescendo/decrescendo is clearly delineated. The passion that is the hallmark of U2 songs is every so present and utterly convincing.

My other amps:

I bought my FEEL HP200SE about a year ago. It is a tube/mosfet hybrid utilizing two 12AX7s and two 12AU7s. The looks are amazing and the sound is excellent. However it no leans more towards solid state than valve sound. Changing tubes does have noticeable effects on the sounds though. The bass can go really deep and the amp can sound very punchy. There are times when it runs head to head even with the Darkvoice 337. The detail recovery is exceptional and attack/decay is very fast. Soundstage does fall a bit short of the Darkvoice though. Also, it sometimes has a tendency to be a bit bright. Extreme highs can be fatiguing. Overall, it’s an incredible amp in the same league as the Darkvoice 337. There is one big exception however, and that is in its power. The amp is massive, heavy, hot (thermodynamically, since it runs full class A) and certainly has presence. But when prompted to drive the K1000s, it begs for mercy, clipping at only around 12 o’clock. Had I more knowledge of EE, I could explain this problem. Anyone have suggestions?

I built my M^3 in the middle of last summer. I started a Pimeta before it as a warm up, having read it was supposed to be simpler and easier to finish. I had a terrible experience with the TREAD power supply (many thanks to MisterX for helping me out) and ended up finishing my M^3 + STEPS before the Pimeta. The M^3 astonished me and almost made me regret buying the FEEL. This amp had some much power! Whereas the FEEL failed to push enough voltage into the K1000s, the M^3 substituted with great ease. The M^3 was faster and punchier. It was surprisingly warm and a ridiculous bargain (thanks AMB + Morsel!) But the FEEL still held a slight edge in musicality. However, sometimes shear force is convincing enough to forget those differences. The bass boost is also brilliant, perfect for my DT880s. In the end, what led me to choose one amp over the other any particular day often depended on shear convenience. The FEEL needed longer to warm up and turning tubes on and off was bad. Both amps got about the same listening time though. This status quo has obviously been ripped apart with the addition of the Darkvoice 337 now.

Tube Rolling:

During that week while I waited for the Darkvoice 337 to arrive, I began reviewing the Darkvoice 336 threads for advice on tube rolling. I put many 6SN7s on my eBay watchlist. Most online sources spec the Darkvoice 337 as using the same preamp tube as the Darkvoice 336. They look exactly the same, which is probably why there is such confusion. Luckily I did not bid on any of these 6SN7s and bought a few 6SJ7 instead. I also bought a few 6AC7 tubes and 2 sets of 6AS7 tubes. I don’t think the 6AS7 power tubes make much of a difference. I haven’t really tested their differences. The preamp tube is another story. I bought a pair of Sylvania 6SJ7s and Amperex 6SJ7s. They were merely okay. I didn’t notice much difference from the stock tube. The 6AC7s were much more interesting. I first tried a pair of RCA JAN 6AC7/1853 tubes. What’s this? Hum? Very bad, what a mistake to buy this tube. It was also microphonic like no other. Moving my mouse up and down to move the cursor across the screen could potentially induce a reverbation I could pick up in my headphone. If I tapped on the amp chassis, I could hear my tapping. But the music that came out was phenomenal. There was a noticeable increase in detail. I did not want to move back to the 6SJ7s or the stock tube. What about the hum, surprisingly, after a few days, it went away. Amazing! Encouraged, I bought a few more 6AC7s. CBS Hytron, that was a pretty decent company. Their 6AC7 hummed like crazy and it did not go away. I tried a set of Ken-rad JAN 6AC7s, hummed at first, but went away after a few days. Moral of the story? 6AC7s are fine, but make sure their military grade.

I also ordered a set of 7C7 loctal tubes and make a pair of adapters. The tubes haven’t arrived, I will post impressions later. I might get some 6080 tubes in the future as well.


All three my amps sound incredible. After extended listening sessions, their sound signatures start to converge and I have an increasingly hard time making out the differences. Any differences are very minor and if I were multitasking, would be lost in my attention deficit. I am very satisfied with my purchase, harboring absolutely no regrets. I would highly recommend this amp to anyone looking for a high end OTL tube amplifier.
post #2 of 909
anyplace in Shanghai sells it? thx!
post #3 of 909
Wow, great review!! I knew you were going to write a review but I didn't expect it to be this long!

Well, the review is absolutely right! We had a one or was it two hours listening session comparing my dynahi with the 337, both performed exceptional and at the levels of these amps they ought to be. The main difference between the two is that the 337 is smoother, tubier (obviously), had more impact and slight wider soundstage. The dynahi imho has the edge on speed, resolution (not by much). Ultimately after 1 hr of listening, I couldn't really tell the difference that much anymore, got lost in the music and just decided to enjoy them.


BTW, we should do an UCLA meet!
post #4 of 909
Thread Starter 
Here is a link to the manufacturer administrated forum.

Here is a thread (in Chinese) about Darkvoice 337 tube rolling.

anyplace in Shanghai sells it? thx!
This thread lists all the Chinese distributors for Darkvoice. Looks like there are two stores. You'll have to call them or search for a website on www.baidu.com
post #5 of 909
Hi, What did you recable your beyer with?
post #6 of 909
Originally Posted by Fang View Post
Hi, What did you recable your beyer with?
Looks like Cardas, which is really popular with dt880.
post #7 of 909
Thread Starter 
I used Canare Mini Star-Quad. There is very little, if any sound difference, IMO. The cable is just much more sturdy. The K1000s have a Canare Star-quad adapter cable.
post #8 of 909


As a owner of the darkvoice 336, I have been through many power tubes including Ken Rad, RCA,National Electronics all 6as7g.
I found(along with Fitz who tube rolled a lot of them also.I know he tried catham,tung sol and many others) that the 6as7g does have an impact on sound.And we both settled on none of the American tubes but rather the Russian Svetlana Military tubes 6h13c(6as7g equivelent). You can get them on ebay for about 8 to 9 dollars apiece shipped.Between I and Fitz we probably tube rolled 10-15 different tubes and both came to the same conclusion independintly.
Hope it helps
post #9 of 909
But when prompted to drive the K1000s, it begs for mercy, clipping at only around 12 o’clock.
Op-amps reaching their limit under high load. Give it better op-amps and give those more voltage to work with and the issue should go away... (matching impedance between k1000 and the amp would help too, but I am not sure how exactly impedance transformers influence the quality of the signal).

Excellent review, although I wonder how would this amp work with lower impedance headphones? Although low impedance issues are not difficult to fix, additional impedance is probably the easiest thing to add in the chain. Also how do you feel about its performance with classical through dt880s?
Also, what power adapter do you use? Sorry to be asking 10000 questions >.< Just bought 337's lil brother 332, while sitting with an hd595, and am wondering about ways to get the best out the amp (332 is supposedly very similar to 337), apart from tube-rolling.
post #10 of 909
I compared the Darkvoice 337 against the Doge 6210 at Mike's apartment. What a blast! Mike was not only super cool, but had amazing equipment. Well, to me it turned out to be more of an OTL Pentode (337) versus OPT Triode (Doge) tube amp comparison. They turned out to be polar opposites, and definately a matter of preference.

The Darkvoice 337 is an amazing amp! It is huge, and beautiful, with no hum. Sizewise, it's about twice that of the Doge. Coming from transformer-output SET amps like the Doge 6210, at first I thought that the Darkvoice 337 sounded like a solid state amp, since it did not have midrange bloom typically associated with tubes and was very clean-sounding. But then I A/B tested the Darkvoice 337 against a real solid state amp the M^3 (with STEPS power supply), and the Darkvoice sounded more lively, impactful, and dynamic. Mike says the 337 is said to sound similar to the 332 but better overall. It has tighter bass than the Doge 6210 and a cleaner midrange. The highs were very similar on both amps. I thought that the M^3, Darkvoice, and Doge 6210 were equally detailed, with the headphone being the limitation. If you just want to buy one amp and nothing else, the 337 might be the amp to get. It does what an amp should do, which is faithful amplification. That it does very well. It presents the music like it is, rather than sugar-coat it like the Doge. And did I mention the tighter bass? It drove the low impedance 25ohm Denon D2000 very well, which surprised me since tube amps have low dampening factors. The Doge made the bass on these Denons a little flabby in comparision (but definately something I can live with). The imaging on the Darkvoice is also superior to the Doge 6210.

On the other hand, if you already own a solid state amp, the Darkvoice will sound very similar so you are better off with a "tubey" tube amp like the Doge 6210. Harmonic distortion specs support this observation. The Doge has plenty of midrange bloom, expanded soundstage, and a sweeter midrange with greater emphasis on the vocals. It's more emotional and natural-sounding to me, but this effect could be in part because I am more used to this amp. It has the prototypical SET tube sound that some like but others dislike. It synergizes better with the K701 because it makes the sound more "full". I should note that my Doge was lightly modded. The gain on the Doge is higher than the 337, so much so that anything above 10 o'clock is useless. Replacing the 12AX7 with the 5751 should remedy this. The Doge also has greater max output than the 337, which is no surprise since it's transformer-coupled. But the only time this matters is when you use DACs without an I/V stage.

In short, while the Darkvoice 337 was technically superior in all aspects, and more neutral, I still prefer the Doge 6210 for its SET presentation of the sound and its better synergy with certain headphones. The Darkvoice 337 sounded like a good solid state amp, with some differences. It is probably in the same class as the Dynahi, probably livelier but won't have the massive bass impact (it is still very amazing in its bass qualities, though). Too bad the Dynahi wasn't represented in our mini-meet, but we did have the M^3 at hand and I already mentioned that I preferred the 337 over it. In turn, the M^3 is superior to the Gilmore Lite IMHO.

Something peculiar to the Darkvoice 337 is that it has two power switches and two volume controls (one for each channel). Channel matching turned out to be much easier than I anticipated, but it could be tiresome in the long term. This is definately a dual mono amp. If this were my own amp, I would mod it to use only one volume control and power switch.

Headphones tested were Denon D2000, AKG K701, Ultrasone 2500, Beyer DT880, and Beyer DT990. Various DACs were used. All these amp comparisons are relative and many people would not even be able to hear the difference. The choice of DAC has a far greater impact on the sound than the amp.
post #11 of 909
When did this come out? I don't remember seeing any threads about a new Darkvoice.

EDIT: Just curious, but does the amp use a stepped attenuator? If not, then how do you keep the left and right sides equal, I imagine you could drive yourself crazy trying to get them to sound the same.
post #12 of 909
Great review as always, thanks for taking the time. I like the power of the hybrids and most of these designs I have heard tend towards a solid state sound in terms of dynamics and bass impact.

The 337 is on my radar.
post #13 of 909
just curious; isn't it more logical if it comes with one volume knob and one flipping switch to turn it on?
post #14 of 909
True purists love the 337 dual mono. You rarely see this anymore because it is more expensive (double). Some may argue:
-there is less crosstalk
-two separate isolated power supplies are more robust than one for both channels. This may(in part) contribute to a more dynamic sound.
-Two volume pots allow for more precise channel tracking
post #15 of 909
Thread Starter 
EDIT: Just curious, but does the amp use a stepped attenuator? If not, then how do you keep the left and right sides equal, I imagine you could drive yourself crazy trying to get them to sound the same.
The amp has regular variable pots. Yes, it does drive me crazy sometimes, trying to get exact level matching. I keep volume fairly constant though, so it's not that huge of a problem.

just curious; isn't it more logical if it comes with one volume knob and one flipping switch to turn it on?
Since the amp is a dual mono (separate power supplies, separate gain stages) setup, the designer decided to highlight that fact with two switches and two pots.

Various DACs were used. All these amp comparisons are relative and many people would not even be able to hear the difference. The choice of DAC has a far greater impact on the sound than the amp.
We compared my Zhaolu D2C (CS chip, LM6172 opamps) with Philip's D2.5 (AD chip, Zapfilter out) and a DAC-AH (with passive bypass). The source definitely made the biggest changes. Which one was better? It's a matter of personal preference.
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