It is clear that the signal is not amplified in the tubes, but somehow participates in the work. A circuit diagram is very difficult to draw, because the circuit is on both sides of the board and the details are too small. The preamplifier is made of a chip JRC4558. No, it's not in the same league as my Pete Millett-designed Wheatfield headphone amp, but it's much smaller and in fact its stepped volume control has better low-level channel matching! I haven't gotten into tube rolling with it, but there are several NOS 6688 tubes that are reported to take it to a different level. All I can say is I'm satisfied. I was turned onto it by a recording engineer friend who's using it to monitor remote classical concert recordings. He was quite smitten by it.

Corelli Violin Sonatas Op5 - Elizabeth Wallfisch, Richard Tunnicliffe, Paul Nicholson, Hyperion Records Despite its mini size(can be hold with one hand), the output power is improved to 100W(50W*2) with the upgraded chip. You will be amazed by its output power compared to its size when you see it.

I disassembled a Nobsound MS-10D MKII and found it was an imitation of a tube amp. An empty box was attached on the top of the amp, that pretends to look like a real tube amp. In the box suppose to be three transformers. One is for power and two for each channel for matching tubes with speakers.

We did our comparisons using the following two recordings, A-B'ing one and then the other over the course of two hours: This little desktop amp is quite good, and does a solid job at amplifying music on small bookshelf speakers to a level where you can use it for basic music listening, can't get loud loud of course. Owners of the amp argue on the forums which Chinese or Russian tubes sound better. There was reported that Russian tubes sound much better, and the tubes with golden grids make the best sound. I think they are a self-hypnosis. Unfortunately, I do not have other lamps to judge the disputants.Connectivity is really the only main issue I have with it. While Bluetooth works just fine (and disables when connected with USB) but is not super intuitive. Also when connected via USB to a computer the volume control on the device yields some rather unpleasant noises when you adjust the volume directly on the connected computer (Windows tested here), as it tries to turn up the signal volume only to realize that USB connectivity comes as clean signal only so it goes up and down a lot before finding the signal level. We need to mention that with the USB input, music can be played losslessly(Like connecting with a computer. By the way, you don't need to install a driver). You will be surprised by the sound quality. It's a pretty decent hybrid amp, similar to a more powerful starving student hybrid. I think it's reasonably priced, given the build quality is actually pretty good. The issue of the tubes being overfed the above link notes has been fixed, as they're now fed a more tube-healthy 6.3. Essentially the tubes act as a pre-amp, which gives it the "tube sound" people are after: a small mid-bass bump and a small lower/mid treble bump (depending on which tubes you use). But it gains the benefit of a solid state power stage. Switching the tubes around, it does noticeably change the sound of it, so the tubes are more than decorative. I think the tubes form a delay time either opening or closing a transistor or chip. I'm sure that the amplifier will work with any other tubes having same pin arrangement. This is Nobsound's new power amplifier in 2023. Based on our previous product, we enhance its output power and improve its functionality, while still keep its mini size and elegant design.

Supporting AUX/USB/Bluetooth input. You can enjoy your music in different ways. The Bluetooth function is also upgraded to 5.0. Now it is more stable and faster. There is only one power transformer under the box, which delivers 17V to output transistors, 7V to microchips and 6.8V to tubes. As we see there is not the high voltage for the tubes. The transformer is not high-quality, noisy. I had to repair it. From a consumer point of view, it was just amazing to note the two sounds shared more than they differed. Perhaps this is causing some to conclude that the tubes are merely decorative. But, comparison to a well-designed larger solid state amp helps highlight the Nobsound's tube character.