Has anyone heard of Shuguang s200mk before?

[Oscarshock]

I knew Shuguang was a manufacturer of vacuum tubes but I didn't know they even produced hifi components. I saw this tube preamp online and had only a little information about it so I sought more information from the Chinese website and here is what I got.
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This is a tube preamp for the line stage only and its schematic is shown below, however, I can't confirm the accuracy of the schematic since I found this on a Chinese forum instead of the official website. Nonetheless, according to the post in that forum, it claimed that the circuit is developed based on the srpp circuit, which I don't know what is it either, but it really looks like a very simple circuit compared to some vintage line preamp that I saw.



Does anyone have first-hand experience on this preamp and what is your impression? What is your judgment of this preamp based on the schematic and the interior?

Thanks in advance for all your comments!

 

[EL504]

The gain of this preamp will be around 47 x (= 33.5 dB), which in most cases is way too high for a line stage preamp.

Personally, I don't like that the heaters of the EL84 and the 6Z4 are not grounded 'hard', but only capacitively through the capacitance the windings of the power transformer constitute, even though you see this being done like this more often.

One side of the heater winding of the 6Z4 could be connected straight to ground. But this is not possible for the heater winding of the EL84 since the maximum heater to cathode voltage of the EL84 is 100 V while the cathode sits at around 250 V. A solution could be to connect one side of the heater to the cathode of the EL84, or to the middle of a voltage divider (two resistors and a capacitor parallel to the bottom resistor, connected between B+ and ground) that sets the voltage to something 200 V. But to do this safely, you have to be sure that the heater winding on the power transformer is isolated well enough to withstand a dc-voltage of 250 V.

 

[Oscarshock]

The gain of this preamp will be around 47 x (= 33.5 dB), which in most cases is way too high for a line stage preamp.

Personally, I don't like that the heaters of the EL84 and the 6Z4 are not grounded 'hard', but only capacitively through the capacitance the windings of the power transformer constitute, even though you see this being done like this more often.

One side of the heater winding of the 6Z4 could be connected straight to ground. But this is not possible for the heater winding of the EL84 since the maximum heater to cathode voltage of the EL84 is 100 V while the cathode sits at around 250 V. A solution could be to connect one side of the heater to the cathode of the EL84, or to the middle of a voltage divider (two resistors and a capacitor parallel to the bottom resistor, connected between B+ and ground) that sets the voltage to something 200 V. But to do this safely, you have to be sure that the heater winding on the power transformer is isolated well enough to withstand a dc-voltage of 250 V.

Thank you for your informative reply. There were only a few posts about this preamp in audiokarma and the preamp was supposed to pair with the shuguang power amp. However, according to the few posts I saw, it appeared that there does exist some sort of loudness issue.