Xduoo Ta-26

disclaimer:  The Ta-26 was sent to me for purpose of this review and tube rolling article by Xduoo.  I have no financial interest in Xduoo or any of its distributors.  For more information about the Ta-26 see Xduoo’s website.    Don’t forget to read the tube rolling article as well as the review covers the Ta-26 with stock tubes.  Improvements in sonics can be made by tube rolling so I encourage everyone to read the tube rolling article and enjoy trying out different tube options in your amplifiers as well.

 

Unboxing / Packaging:

The Ta-26 is a large heavy amp and packaging reflects that.  Heavy cardboard and closed cell foam padding with the tubes in a separate box with foams cut to precisely fit the tubes.   The Ta-26 is certainly safe for shipping in its factory packaging but lacks any presentation for retail applications.    Unpacking the box finds the amp, power cable, and the two tubes needed to start using the amp right away.   The tubes are listed as 6N8P and 6N5p but remember these are the Chinese tube designations and in this case do not match the Russian tube designations.   In US/European terms the tubes are a 6AS7G and 6SN7GT.

 

Build/Fit:

The Ta-26 has an all anodized aluminum shell of heavy gauge aluminum giving it solid heft and good heat dissipation.  The unit is approximately 5 inches wide, 10 inches deep, and 6 ½ inches tall. Total weight is nearly 9 lbs.    The sides and rear of the unit have vents cut that also aid in keeping the unit from overheating.   Metal surfaces are warm to the touch after a few hours use but not uncomfortable and certainly not fire hazard material.   The front face from left to right has the power switch, 6.3mm jack, and volume knob in contrasting red anodized finish that really jumps out against the gray backdrop.   The rear face has a fused power plug, a pair of RCA inputs, and a pair of RCA pre-outs.    Compared to the Bottlehead Crack or Darkvoice 336 (both of which use similar tubes in similar circuits) the Ta-26 is more compact and uses heavier gauge aluminum than the standard Darkvoice.

 

Internals:

The Ta-26 is a true output transformer-less (OTL) amplifier relying on the 6SN7GT driver tube and 6AS7G power tube to do the work.  so why does that matter?   Tubes put out a lot of voltage but not a lot of current and often have a very high output impedance.   One way to “fix” that is to use an output transformer that lowers the voltage, increases the current, and reduces the output impedance.   You may have heard something about needing an output impedance no higher than 1/8th of the impedance of the headphone.   This is a simplification of the calculations for Damping factor which is a ratio of the load impedance and output impedance.   The higher the damping factor the more control the amplifier has over the driver.     Output transformers lower the output impedance and allow tube amps to be used with headphones they otherwise would not be suited for.    The downside is transformers (good ones at least) are often the single most expensive part in a tube amp.   It is not uncommon for the output transformer to cost as much as all the other components of the amplifier combined.     This is typically the reason for OTL designs.  They reduce cost and circuit complexity but do limit the utility of the amplifier to only high impedance loads (150Ω and higher).      The Ta-26 does its best work with 300Ω and above headphones and shouldn’t be paired with headphones having an impedance below about 150Ω.     Xduoo documentation lists 60Ω as the bottom of the range, but remember that impedance is frequency dependent so a headphone with a nominal 60Ω impedance may have dips substantially lower than that and is thus not suitable.    Sticking to models at or above 150Ω gives enough breathing room that even if impedance drops at different frequencies, it should still be above the limit of the amplifier.    As is typical of OTL tube amps,  THD+N is <0.1 and SNR of 120 dB which won’t compete with solid state designs for numbers, but tubes bring their own flavor that solid states don’t offer.    Output power is listed as 500mW into a 600Ω load which is very respectable and remember that the Ta-26 is listed as best suited for headphones from 60Ω to 600Ω meaning the least power available to drive a headphone will be 500mW and as impedance decreases the power climbs substantially.      The amp also delivers up to 16dB worth of gain which even with 600+ ohm AKG headphones gives more than enough headroom.

 

Sound:

The combination of the 6SN7 pre-amp tube and 6AS7 power tube has been around for nearly 50 years and are used in both audio playback amplifiers and guitar amplifiers quite frequently.   The Ta-26  uses a very time tested design as the earliest schematic I could find to a 6SN7/6AS7 powered amplifier was from 1948.     Since this is a well tested design with Xduoo having the benefit of many who has come before them, I expected great sound.    My notes here are limited to the stock tubes and set the baseline for tube rolling the amplifier.   I will release a tube rolling article following this review as time permits.    I used several different headphones including Sennheiser HD800 and HD700,  AKG 240,  Beyerdynamic 990, and Audio-Technica ATH-R70x.

Regardless of which headphone I used, the Ta-26 produced a very “tube” sound, warm, wet, and smooth.   The Ta-26 doesn’t have the crispness of a solid state amp but does a great job of delivering engaging laid-back performances with no harshness or fatigue.    When using the terms warm, wet, and smooth to define performance it would be easy to assume slurred or muddied sound with loss of some attendant detail, but honestly while the presentation is slightly thicker than that of a solid state, detail retrieval is still quite good.

At the low end, the Ta-26 delivers good rumble and slam with plenty of energy to give big hits a nice visceral punch (albeit none of my high impedance headphones are known for being bass cannons).     For big bass hits the Beyer 1770 Pro with a 250Ω impedance is the best mating for the Ta-26.

Mids are nicely delivered with good fluidity and strings have a nice tonality.   The stock tubes do seem to have a mild recess in the true/upper mids but not enough to make vocals sound distant or out of place and it does keep the Ta-26 from sounding splashy or glaring.

Treble is well rendered as well with good air at the top, good detail, and a non-fatiguing presentation.    This is the amp for pairing with the HD600/6xx/650 family as it brings out the sub-bass and treble that are so often lacking when paired with one of the common solid-state amps available today.

Soundstage is well dimensioned and is much more of a function of the headphone than the amplifier.  When using the HD800, it had the spacious stage expected but when switching to the DT990 or 1770 the stage is more intimate but maintains reasonable proportion.

Describing the sound of a tube amp is always somewhat dependent on the tube complement that is in use as they can and do influence the signature.     I’ll cover more on this in the tube rolling article but suggest if you aren’t familiar with “mouse ears” and own a Ta-26 it might wise to look them up.

 

Comparisons:

These two amplifiers were selected for comparison as all use very similar tubes all use similar designs.   None is a direct clone of the other, but all three are close enough to be considered variations on the same circuit.    Adding the speedball to the crack can alter that enough to disqualify it as it raises price considerably and alters the design substantially as well so this comparison is limited to the three base model systems without alterations.   The Crack uses the 12au7 instead of the 6SN7GT in its standard form but many have been altered to use the 6SN7GT and changes are fairly minimal to do so.

The Crack and DV are more easily DIY’d than the Ta-26 as the case leaves little room to work in and modifications require alterations to the circuit boards.  The DV and Crack are both point to point wired which makes trading out components much easier.   I mention the B+ voltages of the two comparison models below so for sake of reference, the Ta-26 measured at 169V.

 

Dark Voice 336e:

At the time of my writing, the DV was available through Drop at a reduced price of $250 but standard retail is even with the Ta-26 and both the DV and Ta-26 are less expensive than the Crack.  The DV casing is a little thinner and less finished feeling than the Ta when placed side by side, but both are solid with mostly metal construction and no worries about durability.   To access the internals on the DV, one has to remove the screws on the bottom of the unit and then has access to all but the power supply transformer (and even that requires removing the bottom to get to the attachment screws).   Most of the DV is point to point rather than relying on PCBs like the Ta-26 does so those who want to replace a single capacitor or resistor are likely to find it easier to work on that the Ta-26 and similar to a pre-built Crack in a some regards.     The trade-off is the DV pushes the tubes the least of the three so delivers less output power   B+ Voltage on the DV sample I had measured 142V which puts it considerably lower than the Ta-26 and way below the Crack.   I’m certain that with a few mods this could be increased but again, this brings cost back into question as a replacement high quality transformer for increasing input voltage can run several hundred dollars depending on what the user desires.

 

Bottlehead Crack:

On the plus side, the large DIY community around the Crack gives it a couple advantages.  First it can be built closer to the limits of the tubes since its builders understand tube theory and mechanics and can tweak the bias current, resistors etc.. to allow for best performance.   Second, a ton of information regarding modding the Crack for specific applications allows users to tune their amplifier to their exact needs.   The downside is, the Crack is sold as a kit so if you don’t have the requisite skills you’ll have to find a builder to help you at additional cost.     Most people start out with the base model or a slightly upgraded version and then add and tweak as they go.  This means what starts out as a $325 kit (shipped) can quickly become $1000 amp with the speedball mod adding $115, adding higher quality caps and resistors $100, and upgrading the power supply (this can reach $1000 by itself if you want to go nuts).     My Crack has been heavily modified over the years so probably isn’t the best stock comparison as it has the speedball addition and a number of other minor tweaks and upgrades.   As a result, my sample has the highest B+ voltage of the lot at 186V.   There is no arguing that the Crack paired with a 600Ω AKG or Beyer sounds fantastic but it requires more work than the other two and can be quite a bit more expensive as well.

 

Thoughts / Conclusion:

I’m a tube guy, everyone knows it so everyone fully expects that I am going to like a tube amp when I have one in for review.  I’ll admit my bias right up front and yes, I do often prefer tube amp sound.   For those who argue that the distortion products make them less desirable than solid state amps, I would counter with “show me a concert hall with perfect acoustics where what reaches my ear is not distorted and I’ll agree with your point”.   The fact is, not all distortion is bad for audio enjoyment.   It might not be the most perfectly faithful reproduction, but it can be more engaging and musical than truer representations.    So does the Ta-26 get an automatic recommendation based on my love of tubes, Nope.   The Ta-26 gets a qualified recommendation based on a couple of factors.   First, if you are a tinkerer and want to change resistors or caps or adjust bias on the tubes, you are better off looking elsewhere.   The board layout and packaging of the Ta-26 do not make DIY easy and will likely be an exercise in frustration.   And secondly, the Ta-26 performs best with headphones of at least 250Ω impedance and is not suited for iems, hybrids, or low impedance headphones.   The Ta-26 is a bit of a one trick pony in that regard, but its a heckuva trick.

If you aren’t into DIY, and own HD6xx or HD8xx series, high impedance Beyerdynamic, AKG, or Audio-Technica headphones and want the most possible bang for the buck, then the Ta-26 makes a lot of sense.    The Ta-26 is a stellar pairing with the Drop/Sennheiser HD6xx with improved lows and highs.  Even ASR who hated a similar amp (bottlehead crack) admitted that objectively it failed while subjectively it sounded fantastic with the HD6xx.      6AS7G and 6SN7GT tubes are readily available and have been in near constant production for nearly 75 years so there are a ton of inexpensive tubes to try.    Those with deeper pockets can invest in top end 6080s from names like Mullard and Bendix and the sky is the limit.