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

Yay, I’m so glad you enjoyed it! The only thing that gives me pause is that a few of us mentioned quality issues with our first units and had to swap them out. Maybe that was just early production bugs and they’ve got them ironed out now.

I put this in a YouTube comment when the video popped up this morning, but just to say it again here: try it with a different DAC. That level of detail retrieval you talked about means it scales pretty well, at least up to the level of the dac1421 which is the best thing I’ve got on hand.

I haven’t measured the Z-out on mine but 5.5 ohms sounds too low given that it sucked big hairy balls with the Clear OG. The mid-bass resonance on that is just super unfriendly to high output impedance amps. This is definitely one for the high-Z cans. HD 58X with the ZMF perf suede pads is mad fun on this too, FYI.

 

More unboxing videos should be like this, straight to the point!

If we're requesting impressions, I'd be curious to hear thoughts about it as a preamp. I'm looking for something to pair with my Decware Zen Triode on a budget, and seems like this could be a good match in the spirit of that amp. Thanks!

 

FYI the 6N5P tube is a Russian noval preamp tube. The one in this amp is a 6N5PJ. I know. Stop being nerdly.

 

There's a $150 shipped CONUS lightly used unit on HF right now...

I'm legitimately super satisfied with my system lately for once and need to be spending money like a hole in my head, so I'm gonna pass on a new toy, but if someone else needs an excuse, lol. One feedback user, so maybe proceed with caution. There are some other less discounted units on a cursory HiFiShark search ($200), but I'd say just go new at that point.

 

Could anybody compare with the sound of a lovely cube (with high end components), with a HD800? This thread is fascinating, I'm trying to dissuade myself from one extra purchase

 

Think it was a Drop TA-88 i checked out for @rhythmdevils and that thing was very noisy(maybe defective tube swapping no effect etc), sound wise it didn't leave much of an impression.

This seems like a fun amp though, wonder how it compares to a fully kitted out crack.

How many steps on the volume?

 

24 steps. Six-seven clicks and it gets too loud for me. Not ideal, but it’s stepped so trade-offs.

 

Thanks Marv & Lindsay for putting out the review. I'm not used to writing impressions so I prefer to let others get down the key points. As this is relatively new to the forum, I thought I should add some more points. But essentially, it's what purr1n said.

TLDR: just get this.

I had the TA-66 since December, and it was by chance that I came across it. I believe it was Apos that sent out their Black Friday sale email and listed this item for sale. It looked like a Darkvoice, and made by Xduoo (which is somewhat more reputable for some of the "Chifi" gear that are out there). Direct wiring. Stepped attenuator. OTL. And it was on sale.

Now, I've advocated for not getting stuck at mid-fi purgatory before, but recently I've come to realize that sometimes the hobby is more about the discovery instead of going directly for the highest tier. I've come to learn from other pyrates that it's also the value, and more important that it's about the connection to the music. So, when the price was right, and that I've always wanted to own a Darkvoice or Crack, I said why not. (As an aside, I don't recall when was the last time I heard the Crack, but I always wanted to build one for myself. I ordered a kit a while ago, and let's just say that it's still 90% at being finished.)

What I'm trying to get at is: if you don't have time to build a Crack (which can be fun), or take the chance on a used Darkvoice, you should try the TA-66. At around $250 it gets you a pretty solid OTL. And this heavy chunk of little amp is a little more than mid-fi.

To add to what purr1n said:

• The TA-66 is more than the sum of its parts.
• The designers did a good job putting in the pieces together to make things gel...within budget
• There are no boutique parts like what you would have to do to jack up a Crack or a DV to get that special sound
  
• Stepped attenuator is actually not bad. I'm surprised that this is included in a sub-$300 amp. You can add attenuators at the inputs, or you can switch your Pi2 to software volume control (instead of fixed) in Volumio or Moode.
• The bass is good. Really good.
  
• The TA-66 is excellent in stock form. You can stop right there and pat yourself on the back for a good purchase.
• The Voshkod driver and the Shuguang buffer work well together giving the amp a mix of tubiness and clarity
• I actually believe the Voshkods makes this more special as I had expected a Chinese 6N2 instead of a Soviet 6N2P.
• The TA-66 can be tuned to be "betterer" with tube rolling.
• Replacing the Shuguang with RCA 6AS7GT [correction: allowed for a more mellow presentation and lent a little more focus.
• Replacing it with a Svetlana Winged "C" 6H13C cleared up the fuzziness and provided more bite. The bass was improved. This is my preference and I'll probably stick with this because I don't want to spend more.
• Replacing the supplied Voshkod 6N2P with a 6N2P-EV didn't really do anything for me, or at least I didn't notice too much difference. [Update: more listening with the EV version leads me to believe that it’s slightly better, but still] I think most people would be good with the stock Voshkod.
• I put in an adapter at the 6NP (front) to use a Soviet-made 6SL7, and this with the Soviet Winged "C" 6H13C are what I settled for. (About another $60 for both the front and back)
  
• The amp is made for high impedance Sennheisers. I enjoyed this with the HD600. And works with the Grado (Hemp) that I tried. My favorite is the Verite with the amp, and I'm sure most ZMFs would be good too.
• UPDATE: Grado Hemp was a bit boomy with the bass…a bit off perhaps due to the impedance.]
• UPDATE: the Audio Technica Refine didn’t really work for me. Not sure if it’s looking for more power from the TA-66. Ohm wise it should work, but I didn’t enjoy it as much as with the HD600 or the Verite.

Compared to:

• DSHA-3F with Verite: it's scarily close in terms of my enjoyment. The 3F has better bass, but I don't think the TA-66 is that far off. The 3F is clearer and has better control, and for 10x the price it should. But I find the TA-66 calling me more at the moment.
  
• Vali 3: different expressions of tubes. The Vali 3 hits hard, and is very clean. The TA-66 is more fluid. The Vali 3 is more versatile in that you can use more headphones with it while the TA-66 is just begging you to use higher impedance transducers. I think you can own both and still justify why you need two different tube amps. UPDATE: I think the Vali is still the budget amp champ.
• SW51+: tough call, but it's more like the Vali 3. It's "cleaner" but doesn't have that OTL sound.

Closing thoughts:
There is good. There is value. The TA-66 is excellent and a bargain.


UPDATE: as indicated by AtomicBob’s measurement, there can be some noise transmitted from the mains. I thought I noticed the same but I’m beginning to think it’s noise coming from the Yggdrasil GS2 into the RCA. Anyway… It’s not perfect, so if you’re looking for that in a $250 unit you might be disappointed, and there are a few members here who have experienced issues with noise from some batches. However it’s an immersive amp and I still think it’s an excellent value for high impedance cans (except the AT Refine that I tried briefly—could be me but the TA-66 might not be powerful enough for it).

Also, I am finding NOS 6SL7’s on adapter can be a little microphonic. It could just be my luck. Might try new manufacture ones if I find good deals.

[Edited for clarity and updates]

 

Hm, I didn't feel like it did anything special with the SR325x. I'll give it another try back-to-back with another amp like the Unity to see if there's something I'm missing.

 

So this means that the 6AS7 crack tubes can be used in this? (I have a bunch) I assume this also means the 6080 can be used?

 

Yes without any adapters, can use the same Crack/DV power tubes 6AS7/6080/7236 etc. The input tubes, however, you'd need an adapter to roll alternatives (e.g. 6SL7).

 

Trying the TA-84 with the DCA Noire X. Works fine so far. For obvious reasons, I'm not too hot on plugging the 8-ohm Para in it.

It's really an OTL PP? Will have to unbutton it and take a look.

EDIT: Nope, audible distortion during bass hits. Can't really handle high current.

 

Actually I think I tried an RCA 6080

 

Yes, Grados now have bass!

 

From this picture it is obvious it is classical cathode follower with Zout c.a 200 Ω.
Just well designed and built.

 

I believe @Hrodulf was referencing his TA-84 amp with his statement

 

How does this compare to a stock Crack?

 

I just gleaned at the power figures. The TA-66 does 200mW@300Ohms while the TA-84 only does 84mW. At 100ohms it can only muster 44mW. No way the TA-84 is a PP.