AIYIMA T20 Tube Pre-amplifier Review

[amirm]

Here's the thing: Anyone who buys a tube device wants tube sound. That warm, fuzzy glow that comes from generous, heaping helpings of second harmonic distortion. It's to be expected that it's SINAD will be in the 40's or 50"s in the same way it's expected that a Python will swallow a live rat whole. It's just its nature.

The "warmth" they think they are getting comes from their eyes looking at the glow of the tubes and preconceived notions of the same. I have listened to many tube products. They simply sound muddy and then get bright as distortion goes up. Sometimes they have high impedance which can combine with the speaker to change the balance and even boost some room modes. But none of this is a function of the distortion.

 

[AnalogSteph]

And from AIYIMA web:

Tubes are driven from DSP and buffered by LME4562. Then you can do almost anything.

Please note that the tube is inside the opamp feedback loop!!

So it would appear that the vacuum bulbs are being used much like you would be adding a discrete JFET input pair (or the like) to an opamp. Starting at fairly high level means that tube voltage noise is kept in check, the +180V supply keeps distortion low, and the symmetrical architecture means H2 is being suppressed (more or less well depending on how good pair matching is), allowing H3 to come to the forefront.

 

[Billy Budapest]

1% THD+N should be audible to anyone.

1% THD shouldn’t be audible to anyone. If the 1% figure is primarily due to noise, then maybe it could be.

 

[Power Pop 23]

I am a little curious as to how users of consumer tube audio gear will regard Amir's measurements of the Aiyima T20 preamp. Will the measurements make them regard the T20 as a savior or apostate of tube audio ?

 

[amirm]

It is hard to answer that question as nobody knows what the real value of tubes are to their owners. Assuming it is some "tube magic," that is not measured, then the T20 qualifies just as well as the next tube product. If it is distortion, then they have to admit that they are pouring this constant effect on everything they play. And that it is measurable.

 

[Sokel]

To be correct here not all tubes do H2 dominant.
Here's a well respected example of tubes:


at -2dB input


..and at a healthy, music banging, -12dB input.

Audio Research LS28

(you made me carry stuff as it's not mine but it was fun! )

Of course it's inaudible even against straight DAC to a Purifi, don't fall for H2 and H3, look at its noise. it's silent even with over 100dB sens horns.
Distortion must be pathological to hear with music.

 

[solawind]

Is H2 at 90 and H3 at 80 inaudible? I thought the threshold was about 110 or thereabouts.

You can emulate harmonic distortion with http://distortaudio.org/index.html to check what HD values you can actually hear. I bet h2 should be around -30db to hear anything on real music. And -80db is a waay below audibility, considering db is a logarithmic scale.

 

[Karmacoma]

Cool looking preamp.
Does anyones know how long these tubes are supposed to work properly before needing a replacement ? I'm curious.

 

[wiggum]

1% THD shouldn’t be audible to anyone. If the 1% figure is primarily due to noise, then maybe it could be.

There are published studies that shows 0.1% THD is audible in the treble range AFAIK. Did you try the test?

 

[pma]

There are published studies that shows 0.1% THD is audible in the treble range AFAIK. Did you try the test?

0.1% THD, H2, is audible at frequencies near 1kHz at certain, not high SPL level, but only on sine wave. It is inaudible with music.

 

[Maxicut]

For it's intended audience, this is a state of the art bargain! (currently on sale for USD$140.00). Digital distortion is a completely different animal to analogue distortion, so you can't compare the two

 

[DSJR]

Cool looking preamp.
Does anyones know how long these tubes are supposed to work properly before needing a replacement ? I'm curious.

I can't suggest an exact 'hours' amount as we all play our rigs differently from day to day and month on month as well as how gently they're run in any given circuit, but typical domestic use, I'd suggest ten years or more for these. From long addled memories, I'd say they fade gently rather than suddenly go down as some output valves can (and did in my case). I could also suggest that there are ECC83s and ECC83s out there, some maybe better made and lasting longer.

Don't some of these smaller signal valves have some built-in microphony to them, which helps with that wonderful 'sonic halo' that good valve gear seems to add? There was a short-lived UK company (Tech-Tube?) that came briefly out of the Mullard/Philips CRT industry when that ended, which had perfected the working-end of CRTs (basically large specialised valves) for long, efficient and reliable life. They made an ECC83 equivalent I recall, using this acquired CRT tech knowledge as best as they could and I seem to remember that these new valves weren't liked as they were too 'clean' as in solid state sonics. They had to add some microphony to get the sound the valve afficianoados wanted. The business had no sooner got going wehen something happened to pull the plug on them. I hope I have this right -

Sad News About Blackburn / Tech Tube

Or lets say, I think its sad. After their IMO heroic attempt at bring the Blackburn factory into the next decade with new production advanced valves, they appear to be doomed. http://www.lancashiretelegraph.co.uk/news/blackburn/4642860.Historic_Blackburn_firm_in_administration/ AN HISTORIC...

www.diyaudio.com

 

[Ropeburn]

Distortion must be pathological to hear with music.

Which is why in actual musical use, the fun only starts at 100%.

 

[EJ3]

Naked tubes.... ? Temperature wise, breakable, 160V, electric safety? Are we sure this will fulfil any safety regulations? I know it looks great but anyhow, with children in the house it can be dangerous. I can imagine CE or UL won't be happy.
Furthermore, I voted poor for my safety concerns.

Teach your children well.
(when I was a child [my mother is Austrian]) and was of the age that I could not yet see the top of the stove but could reach it with my hands, she turned a burner on & grasped my hand firmly and held it close enough to the burner that my (and her) hand could feel the heat & she said the German word for hot. I never once reached up there.
In my life, I had hundreds, if not thousands of small but very memorable lessons like that.
That was teaching, not just saying. You need to teach them to think (before they do), not just be a bystander & tell them. Because later in life, spoken lessons may be forgotten.
And the protection on something that the government (or some other organization) says is safe: may have failed in an unexpected way.
I know young (usually adults) that get theses lessons in a nasty way: such a working on electric golf cart & their wedding ring touches a battery connection & they are ground (which truly does not help the wedding band finger).
These types of things may (nothing protected by something devised by man is 100% failsafe) not have happened had they been taught things that they need to know in childhood.
And many say, "my parents never showed me that this could happen".

 

[garbulky]

Has @amirm checked if the tube is actually in the audio path? I'm skeptical it's doing anything but mood lighting

 

[amirm]

Has @amirm checked if the tube is actually in the audio path? I'm skeptical it's doing anything but mood lighting

I can't check but schematics provided show that it is.

 

[SMen]

Just curious what some people here's recommendations would be for a balanced pre-amp with perfect channel matching at this sort of price point, for comparison purposes. The Schiit gear is much more expensive. AUDIOPHONICS AP310-PREAMP do one with volume control that takes the same approach MUSES72320 - probably higher spec'd. I got my T20 delivered for 118GBP.

 

[milosz]

The "warmth" they think they are getting comes from their eyes looking at the glow of the tubes and preconceived notions of the same. I have listened to many tube products. They simply sound muddy and then get bright as distortion goes up. Sometimes they have high impedance which can combine with the speaker to change the balance and even boost some room modes. But none of this is a function of the distortion.

I've listened to a number of tube preamps and amplifiers. I had a Conrad Johnson PV-5 and then later a PV-10. I thought that they sounded a little rolled off in the treble, but otherwise OK. Not "sweet" in any sense. I sold them.

I currently have an H-K Citation II with the McShane modifications. I use it to drive Quad ESL-57s, and it sounds quite good. Sounds very much like the solid state amplifiers I've used with those Quads- I have an A/B switch, along with individual level controls, which I've set up to compare different amps on these ESLs. Like I said the Citation sounds like most of the solid state amps I compared it against, except one or two solid state amps did sound brighter- unpleasantly so. But most solid state amps sound just as good as the Citation. I have kept the Citation on those Quads because I just like the thing. It sounds good and I like the way it looks. I don't think there is any electronic advantage to it having tubes, except it does impress the Gen Z guys who have seen it. "What are THOSE??"- pointing to the vacuum tubes. I tell them that they are small thorium reactors.

I have another tube amp I use with a pair of 5-inch 2-way speakers (SEAS Millennium drivers, sealed box) - it's an odd Audioromy amp that uses 3E29 dual tetrode output tubes for about 20~30 watts per channel. The output source impedance is kind of high, so this interacts with the impedance curves of the speakers in a way that I rather like. The amplifier is acting as EQ, a kind of tone control. On those speakers it sounds really quite good. Again, not "sweet" with extra 2nd harmonic, but the frequency response irregularity caused by the overall impedance characteristics is something I like. I have tried solid state amps, including class-A amps considered "high end" but they drive the speaker without that coloration, so I prefer the tube amp. I bought the Audioromy amp used for about $200. I can also over-crank it a litte in the bass and the sound doesn't completely fall apart- tubes driven into light clipping do not sound nearly as obnoxious as a solid state amp under the same conditions. Kind of a cool looking amp. Chinese amp, I've used it daily for over 5 years in my workshop and there have been no operational problems- so much for those who claim that all Chinese products are cheap junk.

I had a Dynaco Stereo 70 - there was something wrong with the highs with that design. The treble didn't sound rolled off but somehow there wasn't any detail in the highs. A bit hard to describe, but it did not sound good as far as I was concerned. I sold it off.

 

[totti1965]

Delighted to read the opinion of a tube aficionado! I'm not sure about (but I am going to listen to) this YouTube. I don't actually want 'warmth' from tubes. I bought one of these T20's and I am delighted to read this review (T20 struck me as unusual/filling a genuine niche - balanced - genuine tube gain with decent op amps to handle the outputs). Delighted to see my impressions of the volume control vindicated also!

It enhances the sound to my ears by adding body to vocals and speech. I have "improved" perceptions of stage width and depth. Really interesting imo. I changed the valves to Tung-sols. Not romantic at all. It's a pity a switchable op amp driven bypass could not have been included to challenge the nay-sayers.

Next Wednesday my friend Peter from Cologne, who is an Altec 604-Owner and single ended triode user, and me, we will visit @Heinz R to hear his Tannoy and his MacIntosh C2200 Tube Preamp….., so … yes.
10% subjectivist in me.

 

[wwenze]

Yes, we have more distortion than a solid state design but if one wants that, it would not be a tube product.

The tube product paradox

How much negative feedback can we stuff into a tube amp so we can say "at least the signal still passes through a tube" while providing usable performance?

81dB is already better than some smartphones / MP3 players out there so maybe it's already in the region of usable.

View attachment 482053

Rated SNR seems to be a bit off from measured SNR? Or just different reference voltage?

Furthermore, 20log ( 20uV / 4V ) = -106dB, I'm lost in the calculations