AIYIMA T20 Tube Pre-amplifier Review

[welwynnick]

@welwynnick : Something to add to your legendary table!

I appreciate the suggestion, but the tables that I put together were intended to compile best-of-breed products, in particular, those that would work together in an effective system. For pre-amps and HPAs with line outputs, I was looking for those that could enhance system level performance, rather than acting as a bottleneck. In particular I short-listed those that combined high output level and low noise and distortion, but I don't think the T20 does all that.

 

[Joe Smith]

To my mind, it's an odd and not very useful preamplifier that does not at least have two (ideally three or four) inputs. So this has no use for me, but at least has good specs if someone wants to get a little tube effect into a single source downstream to the amp...

 

[morillon]

I appreciate the suggestion, but the tables that I put together were intended to compile best-of-breed products, in particular, those that would work together in an effective system. For pre-amps and HPAs with line outputs, I was looking for those that could enhance system level performance, rather than acting as a bottleneck. In particular I short-listed those that combined high output level and low noise and distortion, but I don't think the T20 does all that.

I think you're on the wrong track, focusing on certain ASR-style measurements... If it's really about achieving correct and truly usable preamp/amp combinations... it's preferable to first observe the gain-sensitivity-output level compatibilities, the output/input impedance... (and here I'm getting out of the equation regarding the preamp too... the same thing for source/preamp) Afterwards, you can focus on distortion measurements, etc., at your leisure. ;-)

 

[TNT]

No . Nonlinear resistor would be closer.

A not cooked carbon comp resistor ;-D

//

 

[welwynnick]

I think you're on the wrong track, focusing on certain ASR-style measurements... If it's really about achieving correct and truly usable preamp/amp combinations... it's preferable to first observe the gain-sensitivity-output level compatibilities, the output/input impedance... (and here I'm getting out of the equation regarding the preamp too... the same thing for source/preamp) Afterwards, you can focus on distortion measurements, etc., at your leisure. ;-)

The preamp table was indeed part of the much bigger picture.
The priority for me was trying to establish an optimum layered architecture.
One function, one unit, one input, one output and one process are associated with each layer.
Each unit is optimised to perform the one function that it does best.
The preamp is important because :

• It allows the source to work at it's optimum output level
• It presents a high load impedance to reduce the current demand on the source
• It achieves effective volume control while maintaining channel balance and minimising signal degradation
• It has a low output impedance capable of driving any power amplifier (without an input buffer)
• It has a high output level that allows power amplifiers to run at low gain to achieve best performance

 

[wiggum]

I found the plots. Published by Bob Stuart, but AFAIK there is another original source.

View attachment 482435

Edit: this is the source paper. Fig. 3

https://www.meridian-audio.info/public/coding2,P5b2520,P5d.pdf.pagespeed.ce.yeZvG6GuKe.pdf

Nice find!

If I am listenting to music at 80 dB SPL, the 2 kHz component is at ~65 dB SPL (assuming music is like pink noise), so an amp with 0.1% THD should be audible, isn't it?

Of course, I am ignoring psychoacoustic effects.

 

[SSS]

Hello, thank you very much for your attention!

Our T20 preamplifier circuit includes a transformer design that allows the ECC83 (12AX7) tube to reach a maximum operating voltage of 180V. The tube uses anode amplification and works together with the subsequent op-amp stage to amplify the signal. Therefore, it is not just a decorative light, but an important component that actively participates in the sound amplification.

We hope this explanation helps you better understand the design and sound performance of the T20.

Since I have no schematic I just can imagine the use of the ECC83. Looking at the ECC83 datasheet regarding the 180 V. If it is the plus supply voltage then this is in the low end and distortion is higher due to working in the non-linear part of the Ia/Vg curve. If it is the plate voltage so it would be better. The datasheet circuit examples show relaively high distortion values in the single digit percentage. In order to get distortion down according to your provided data there should be high feedback value and a high open loop gain which I assume is also done be the buffer op-amp. Would be nice to see the actual ECC83 circuit schematic.

 

[Robbo99999]

What's the purpose of a tube product that produces distortion at such low level that you wouldn't hear it's effect? Seems like a pointless product?

 

[pma]

What's the purpose of a tube product that produces distortion at such low level that you wouldn't hear it's effect? Seems like a pointless product?

It has been already said several times. Sales, sales, sales.

 

[SMen]

It has been already said several times. Sales, sales, sales.

It has been said, but bears repeating, that having a switchable op amp based active 'bypass' would have been fascinating, and worth reams and reams of additional pages on this thread @AIYIMA take note !!

 

[Ropeburn]

Compared to the sharp sound of Class D, it's much milder and sweeter.

Please. Not this old nonsense again. ;_;

 

[JSmith]

Compared to the sharp sound of Class D, it's much milder and sweeter.

This is a preamp, which are class A or class AB... not class D.

Or are you talking about some kind of cheese?


JSmith

 

[Robbo99999]

It has been already said several times. Sales, sales, sales.

I know it's been said several times, I hadn't read any of the comments when I wrote my post, but I still think it's sort of pointless.

 

[quocheiser]

I understand the hate on this product to a degree, but because it's such a quirky product (like how the Platypus is a quirky animal), I can't help but love it.

 

[Mike123]

I understand the hate on this product to a degree,

Come on, isn't hate. Just don't understanding.

 

[JSmith]

Yeah I had that image in my post, but removed it as the opamps and tubes have been rolled and generally I don't post modified device images.


JSmith

 

[antcollinet]

Nice find!

If I am listenting to music at 80 dB SPL, the 2 kHz component is at ~65 dB SPL (assuming music is like pink noise), so an amp with 0.1% THD should be audible, isn't it?

Of course, I am ignoring psychoacoustic effects.

No, because the chart only refers to audibility of harmonics when listening to a single test tone. As pointed out above by PMA - completely inaudible with music. Much larger tones in the music will completely mask the harmonic tones.

If you want to find out what levels of distortion you can hear in music, you can try the klippel listening tests. Most people can't even manage to hear -40dB (1%).

 

[Sokel]

What's the purpose of a tube product that produces distortion at such low level that you wouldn't hear it's effect? Seems like a pointless product?

Visuals, do you know of anything stronger in life? (even at audio, yes) .

 

[Robbo99999]

Visuals, do you know of anything stronger in life? (even at audio, yes) .

You could buy it if you think it looks good I guess, but for the informed people you wouldn't buy it because it does neither properly (doesn't do the tube sound properly & doesn't do the totally "beyond doubt" clean measurements that we've come to know for DACs/amps recently here on ASR). So yes uninformed people could buy it because they like the look and they'd also likely be buying it because they want tube sound which again they wouldn't be achieving, so they're being duped anyway. Virtually noone buying this product is not being duped, because if you know the measurements neither camp would buy it in the first place. I'll add that "duped" is a strong word to use, and in the strict sense it's not a broken product, but it doesn't offer what it may look like it offers.

 

[Sokel]

You could buy it if you think it looks good I guess, but for the informed people you wouldn't buy it because it does neither properly (doesn't do the tube sound properly & doesn't do the totally "beyond doubt" clean measurements that we've come to know for DACs/amps recently here on ASR). So yes uninformed people could buy it because they like the look and they'd also likely be buying it because they want tube sound which again they wouldn't be achieving, so they're being duped anyway. Virtually noone buying this product is not being duped, because if you know the measurements neither camp would buy it in the first place. I'll add that "duped" is a strong word to use, and in the strict sense it's not a broken product, but it doesn't offer what it may look like it offers.

Is cheap enough only to be a decor item at the end of the day, like a set of VU meters or something.
As is I expect it to pass DBT against better measured gear if noise stays at check, distortion is really negligible.

I have now someone beside me now that tells me that with the right RCA tube (which costs more than the pre) this can go to positive THD+N and also be level dependent

(I have no idea about the claim, he maybe has fun with me )