This preamp was in the workshop for some upgrades and repairs. The main upgrades were to upgrade the coupling capacitors to Mundorf ZNs, and repair the volume motor pot. Finding a replacement motor pot that fits in the space available and is a 500k log pot proved impossible, so I spent a long time stripping the original pot down and rebuilding it. It now works perfectly and the pre sounds very dynamic, detailed and spacious and much improved over the original grainy sound. Ming Da use poor quality coupling capacitors then bypass them with equally poor quality caps. In my view that can introduce phase shift effects and sound is much improved using single quality film /foil capacitors. Those bottle-shaped tubes may look cool but they are horribly microphonic. The 6SN7s are worse offenders-because higher gain-than the 2A3s so those were replaced with some very high spec Russian military valves which again contribute to the overall improved sound.