I'd consider this as a tube buffer, rather than an amplifier. As described, it adds "warmth" to the source material rather than amplify it. My two cents worth ..
zeebeeSo it's just sort of a signal path polluter, then? Honestly, this is probably the most worthless piece of gear I've seen in quite awhile. Might as well just buy some extra-long interconnects and wrap them around a transformer if you want to "color" your sound.
zeebeeOne reason for someone to buy it is that it's a cheap way for someone to play with tube rolling without having to commit to dedicated tube equipment since it can just be inserted in the signal path.
zeebee The benefit of 'tube warmth' is not something you just add along the way. The characteristically good sound of tube amplification is due to the way distortion is inherently shaped when signals are amplified via thermionic emission as opposed to solid state transistors. Since this doesn't affect any actual amplification stage (i.e. pre/power amplification, likely solid state, is still happening downstream), it is just added circuitry between your source and your ears.
zeebeeI use a modded (Mundorf caps) version of this with Sylvania 6sn7 tubes between a Grace m902 and a W4S class D amp. I find it does give some of the smoothness and bloom of a full tube amp compared to the straight SS setup. The difference is not subtle and IMO a worthwhile upgrade to "smooth out" (add certain harmonic distortions) SS systems that may be a little too sterile (or accurate if you are one of those guys)...
zeebeeThis unit is actually a Tube Stage, not an amplifier. Its purpose is to insert (pleasant) distortion between the audio source and the amplifier. They can tame an otherwise "Bright" system and roll off he solid state harshness. As enginerd said it's a cheap, easy and fun way to play with tubes, also known as "Tube Rolling" . Yaqin is one the higher end, less expensive Chinese manufacturers, they produce pretty good products for the money and the build quality is quite nice.
GlowdogNo, it can't roll off the solid state harshness because that harshness specifically comes from amplification of signals using solid state transistors. Since this tube buffer is simply adding distortion before any amplification, you still get the brightness as the now distorted signal still gets amplified in solid state stages downstream. Read "The Cool Sound of Tubes" from IEEE to better understand. http://spectrum.ieee.org/ns/pdfs/08_98_tubes.pdf
AllanMarcusAn actual tube preamp (not what this is) is using tubes to amplify signals. So no, they have not wasted their money. Anybody who buys this thing however IS specifically wasting their money.
dnogsI have an Audible Illusions M3 driving a pair of modded Dynaco Mark 4's, so of course I view this "tube buffer" device as a waste of money. If you want to hear tubes, get actual tube gear, not a tube based façade.
That being said, a nearly twenty year old article is only relevant if you are running a twenty year old SS rig. You might see a benefit if you put this between an early gen digital source and a later gen SS amp stage. And of course, the natural reaction would be, why bother? Spend the money upgrading the digital source instead.