The Amazing $50 Tube Preamp/Buffer
Dick Olsher (December 2020)

During these crazy Covid times I have been spending much more time than usual surfing the web. During one late night session I came across a YouTube review of a miniature Chinese preamp (https://www.youtube.com/watch?v=qghXciQ1pO8&t=165s). I was sufficiently intrigued, and figured that I didn't have much to lose, so I ordered a unit off the Banggood web site (https://www.banggood.com/Pre-Amplifier-Stereo-Amplifier-Hi-Fi-Preamp-Douk-Audio-6N3-Vacuum-Valve-Tube-p-1129374.html?cur_warehouse=CN).

This appears to be an OEM product stocked by Banggood, as I've also seen it offered under different names on eBay. I can't seem to find a schematic or info about the original manufacturer, but it appears to be a rather clever design. For example, the 12 VDC input voltage is stepped up to about 100 volts via a DC-DC converter, which results in a comfortable operating point for the 6N3.

There are two things you need to do after receiving the unit; it sounds decent out of the box, but the magic starts happening after the following two mods:

First, replace the Chinese 6N3 tubes with a matched pair of Russian 6N3P-E tubes.

Second, snip off the wall wart switching power supply and replace it with  a linear DC power supply such as the TekPower TP3005DM Linear Adjustable Digital DC Power Supply ( https://www.amazon.com/gp/product/B00L2OQOOE/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1) which I have been using for the past year, mainly in conjunction with the First Watt B-1 preamp.

The end result is a rather transparent and sweet sounding line preamp. Textures are infused with a little bit of desirable 2nd order THD and tonal colors are vivid as in vintage tube tradition. It makes for an excellent companion to any bland sounding solid-state amplifier. The Bryston 3B-nrb is a case in point. It's a recent acquisition off eBay, and while it's quite listenable, its color palette is rather bleached out. With the Banggood in the chain, the Bryston  underwent a remarkable transformation, Detail and dynamics remained strong points, but it took a giant step toward sounding like the real thing as far as harmonic textures and tonal colors. So now, I'm just enjoying the music, and in no rush to evict the Bryston from the reference system. I also tried it briefly with an expensive tube power amp and was amazed by its midrange finesse and authority.

What more could you ask of a $50 device? OK, to be exact, with the DC power supply and new tubes, the total investment approached $200. But still, this Banggood preamp truly provides an amazing good bang for the buck!