xDuoo TA-66 OTL Tube Headphone Amplifier: A Kind of Magic

Due to the low cost of TA-66 many are now able to be introduced to a true tube topology headphone amplifier. Along with the experience comes a new wave of listeners who might benefit from enlightenment about the nature of tube hum and noise. Here are three links that may provide insights:

https://www.superbestaudiofriends.o...ube-warm-up-time-technical-measurements.3810/
https://www.superbestaudiofriends.org/index.php?threads/tube-sounds.11547/
https://www.superbestaudiofriends.o...t-jr-official-thread.5408/page-24#post-222569

The last link is a demonstration how magnetic fields can induce noise into transformers in a tube amp.

Other things to consider:
1) Always suspect a ground loop first when hum is present.
2) A marginal or defective tube may be the culprit, not the whole amplifier. Change tubes to investigate.
3) Digital devices with on-board radios (Bluetooth, GPS, 3G, 4G, 5G, etc) can introduce noise into the tubes when in proximity to the amplifier.
4) A strong electromagnetic field from some other device may cause introduce hum into the tube amp. Reorient or relocate the amp to investigate.

 

Asking for no reason in particular but given this fully trounces the Garage1217 lineup with respect to powering higher-impedance dynamics and seems to similarly outperform the Vali 3 for the same, how would this fare against a higher-end hybrid like the Lyr+ running in tube mode with respect to resolution of textures, microdynamics, and stage cohesion (not necessarily how large the stage is, but how well-integrated sonic elements are-- delineation and such)? Also guessing that the TA-66 is gonna be more of a proper thwack in the face impact-wise vs a more controlled punch on the Schiit?

I get that they're VERY different price brackets and that the Lyr will have the edge in terms of versatility of deployment due to it being a hybrid topology thing (or SS) ergo having significantly lower OI (plus a really nice relay attenuator vs a questionable one as on the xDuoo) but if this ends up being an overall better amp for high impedance dynamics then that is a compelling thing.

Still never heard a SW51+ but curious how wet+warm=moist the presentation is vs the ZDT Jr. Got to borrow the same one from a friend and was reminded of how much the HD600s really liked it, filled in the lower octaves and helped smooth the slight glare out. Does it seem like the TA-66 might be a bit too warm for an unmodded HD650?

 

I don’t have a modded 650 at hand but I can say that the 600 works well and is not too warm with the stock tubes (Shuguang buffer; Voshkod driver). The Verite Open is a little warmer but it’s not like warmpoo if that makes sense.

The thing is, the TA-66 is not that powerful, but for the Senns they are powerful enough. On my brief time with the Ars Technica Refine with the TA-66, the combo just didn’t gel for me like the 600 did (and I suspect that more power was required despite those being high impedance as well). The 600 just worked and with the bass-ier nature of the amp I suspect that 600 would be better than 650. (I just can’t locate the 650 since the last storage cleanout…sorry.)

I think the 650 would work well if I can triangulate, provided that you have room with upstream sources that can cool or warm up your downstream. Also you can experiment with cables (all copper or silver plated, etc), and of course tube rolling will have an effect.

The SW51+ is not wet at all, and will not beat the TA-66 in the bass area. Although it uses tubes, the SW51 is not OTL. There’s a bit of magic with OTL (done right) but the price of admission is a pair of high impedance headphones. From the TA-66 the instruments just pop right out while the presentation is fluid…it’s like you’re watching a restored version of The Wizard of Oz or something.

Lyr+…probably need @purr1n to weigh in here. What I remember is that it’s very capable, but it wasn’t made specifically for headphones like Beyers or Senns, and you’re not getting that OTL-ness.

If you own a pair of high Z Senns (or Beyers or ZMFs) I really think you can’t go wrong with this budget TA-66. It’s really that enjoyable. If you look at the list of amps that this site recommends for the 800, you won’t find another for <$300. And it’s ready to go with the stock tubes.

Edit: fat fingers. Dang autocorrect.

 

I don't have it with me right now and haven't heard it for a few months, but Lyr 3 was my preferred amp for a long while and never totally fell out of rotation, and TA-66 is on my desk now.

With the headphones that work best with TA-66 (let's say the HD800), it is much better than the Lyr 3. Lyr 3 is -maybe- a bit clearer, and I think has better bass overall (depends on how much you value LF extension - the TA-66 has quite a bit of rolloff there, which can be extremely unfortunate with, say, open-back Senns). I think the TA-66 is better at everything else you mention. Not always by a lot (the Lyr 3 really isn't bad at anything), but... sometimes by a lot.

The Lyr 3 has its own synergies, mind. I suspect the TA-66 has better peak performance with its best pairings, but there are some good headphones like the Focal Elex that work better with Lyr 3. I imagine Lyr+ is the best price-appropriate thing you can buy new in the US for a lot of headphones.

With respect to impact... maybe. TA-66 tends towards realistic timbre, and it has good normal-sounding dynamics for the most part (as opposed to pillowy dynamics or unhinged runaway train dynamics). Lyr 3 does not nail the timbre quite as well, and it has a tendency towards disciplining unruly headphone impulses that could perhaps come off as overly controlled - but some headphones benefit from that. My sonic memory might have some limitations in answering this one better.

I don't really like the TA-66 with a stock HD6XX, the bass boost is just too much for me. I suspect some of this is that I have a warm source, and some of it is maybe that I don't actually like the HD6XX that much.

 

Hi All. Interesting read, this thread. I have had a TA-66 for a few months with no issues. I've found the Thompson 6080 and RCA 6AS7G to be the best factory Shuguang replacement (I've also tried RCA 6080, Tung Sol 6080 and Svetlana Winged C) and Voskhod Rocket Silver Shield seems to work great paired with all of them, but that's just me and my ears. It works well with the several high impedance cans I have (DT880 600/DT770 250/DT1990 250/ ATH-R70X/HD6XX). I'm feeding it a 2.6V input from a Topping DAC and there's no gain or lack of power on any of the headphones although some of them are more tube sensitive than others. I'm curious, has anyone tried using it as a preamp into either power amps or as an ersatz tube buffer? I can't seem to pin down the output voltage or impedance from the RCA's and I don't have a tester anymore. Xduoo doesn't seem to have the spec/respond to inquiries about the spec. Seems to need to be cranked to max to work as a tube buffer which I guess makes sense to a degree. I'm only using that way because I can and it's fun to fiddle with, not because I need to and it's right next to my DAC and SS headphone amp/preamp.

 

TA-66 preamp output impedance measures approximately 150 ohms.
While the preamp output is independent of the headphone output, preamp output drops a bit if headphones are connected.
Unity gain occurs with volume knob set around 1:30 ~ 2:00 o'clock. Will be affected by drive and output tube gm.
See xDuoo TA-66 technical measurements and scroll down to find stepped attenuator gain behavior.

 

Double post just learning the forum software.

 

Ah, that makes sense and is fairly in line with what I was seeing. I didn't notice the attenuator gain behavior chart before, that spells it out quite neatly and yes, that also makes sense RE the drive/output tube as well. Ironically I had it set to position 18 which is right about 0db on your chart so my old ears still work. I'm definitely seeing significant differences between some of the GAS7G's and the 6080's both from an output standpoint +/- (scientifically unmeasured) a couple db. Thanks for the info, that's what I was looking for almost exactly.

 

Does presence of a ground loop depend on which preamp is used? When I swap the TA-66 and Schiit Saga OG in-place (like even the same IEC cord, RCA, same location on desk, etc), I hear no hum in it.

 

Every audio component has it's own internal signal and chassis grounding scheme. Cause of ground loops vary.

Additionally each component has it's own residual noise spectrum. The Saga has approximately 20 dB less AC mains residual noise than the TA-66.

saga preamp technical measurements
xDuoo TA-66 technical measurements

Then, depending on the sensitivity and frequency response of the headphones or speakers, more or less hum may be observable between different preamps.

 

This might turn out the be a very unpopular opinion, but I am personally disappointed with the amp. I ordered it on Amazon to try it out (using the return policy).

I am driving it with Hifiman's EF400 as a DAC (good for the price, not stellar otherwise), using the (shorted) symmetric output.

I am using the amp for my HD800, with the Maxx mod.

My overall impressions are that this amp just castrates the HD800. Sure, compared to most amps in the market, it sounds like quite a great combo. The bass is very full. In my opinion, actually too much so (I would EQ it down if I were to keep the amp). This is another way to say that what makes the strength of the HD800, namely the treble, is very much downplayed by the amp. To my ears, this combo sounds more like a properly driven HD650.

I feel like a lot of detail is lost, and the holography is not stellar either. Sure, you can listen the HD800 for hours with this amp, but is it still the headphone you bought?

I am comparing this amp with a Lovely cube of a friend, modified with high end components. For me it's night and day in terms of what makes the HD800 so famous. The speed is approaching estat realm, while having some amazing imaging. This is not a trait I could find with the TA66. Sufficient bass, to my taste, can be found with minimal EQ.

This might just be a preference in sound signature, but I thought it could be an interesting addition to the discussion as to anyone wanting to impulsively purchase this amp for their HD800 (like I did).

For the budget, it's a great amp, but it's a very colored sound signature - and for me denatures the HD800 too much.

I also would like to point out build quality concerns: I am catching interference, from using my computer, on the left channel only. Swapping cables gives the same result. Using the EF400 in RCA too. This lack of a black background must not be great for detail, so please take that into account when considering my opinion. I do not think that this is the full story though, and the sound signature will probably remain essentially the same.

 

Are all the QC issues known so far related to Amazon purchases?

 

Mine clearly came in an original looking box, I doubt it was opened before/any different because it came of Amazon. But I'd be curious to know if there were other cases.

 

There are things this amp isn't the best at, and you've focused in on some of them. The imaging isn't pinpoint, the transients are not super crisp fast. Other amps will do those things better if you want them. I think this is more of a matter of taste than an absolute weakness; as far as I can tell some people REALLY dislike pinpoint imaging. But I don't think you're wrong to hear those things - I like the amp a lot, but I hear it that way in those respects as well.

It's also true that it tilts the HD800 to be warmer. This is a headphone that has a lot of things going for it in terms of nuanced and detailed sound reproduction, actually being able to do good headstage, etc. It's good enough at these things that people who clearly hate the baseline tonal signature are willing to consider finding a way to live with that if they can keep the other stuff. If you picked the HD800 because you like the tonal signature, though, then obviously anything that pushes too much against it will not sound good to you and this amp would be a bad choice. It's always about understanding what you like, right?

I think the amp is notably good at detail and holography compared to other amps I can think of (though there's some stage width tradeoff for depth), so there's some disconnect somewhere. I don't know about that DAC, but this amp definitely cares what DAC you use. I don't know about that mod either (I looked into it at one point and just ended up kind of confused). I do know the interference would drive me up the wall and make it difficult to listen, period.

 

Received mine from Amazon yesterday and there is no hum, no QC issues whatsoever.

What there is is a WOW factor with HD800S. I've been holding on to and enjoying MJ3 specifically to pair with HD800S for a while, and I acquired Gungnir 2 which improved things incrementally. But when I read people here putting the x duo whatever this amp is called lol above MJ3 I used an amazon gift card to see what the fuss was about, and wow, yes, it is more engaging than MJ3 with 800S. I would describe MJ3 as perfectly mitigating the flaws of 800S to make it shine, whereas this cheap tube amp turns it more into a "lean-in" type magic engagement type of experience. I'm using GS2 single-ended so whatever is lost there versus balanced is made up for and then surpassed by the tube amp.

I haven't yet tried Auteur Classic, my other most used headphone on it, but will tonight. I'm kind of hoping it's better on MJ3 (I think it's great there!) because I love that amp and don't want to feel stupid for holding on to it.

 

What other DACs have you tried? When used with the dac1421 I found the TA-66 to be a great pairing with the HD 800 S, and it very much is still the headphone I bought. It definitely doesn't sound like a HD 650 to me. If you've been using the EF400 as an AIO previously, it might just be that you've double-dipped on smoothing out the transients when combining it with the TA-66.

I enjoy pinpoint imaging, but combining the HD 800 S with a DAC and an amp that emphasize this aspect makes me feel like I'm watching a TV with the sharpness control set to 100. No recording is good enough to stand up to that level of scrutiny.

 

TBH I think the TA-66 is just a bit overhyped. In terms of a uni-tasker driving HD800S, yes, it's pretty damn good but it's also a colored amp for a colored headphone. In terms of a multi-tasker driving everything I can throw at it, Vali3 is still a better amp for even cheaper, IMO. And Vali3 scales just fine with BF2OG and different flavors of Yggdrasil.

 

@abalone : it is good to have alternative opinions. I am not familiar with the EF400 Himalaya R2R DAC and have no idea if it pairs well with a TA-66 or any other 6AS7 OTL headphone amp for that matter. I can say the Holo Cyan 2 is working well with my TA-66.

 

Totally agree. It’s a one trick pony. But it’s some trick, though. The Vali would be my first choice if I were just starting out: cheaper, more headphone (and IEM) choices.