Review on Enhance Your Home Audio Experience with the FX AUDIO Tube Preamp: NE5532 Replaceable Tube and OP Amp Chip, Mini HiFi Stereo 6K4 Vacuum Tube Buffer Preamplifier with Bass and Treble Control, and RCA Cable Compatibility for Amp/Active Speaker by Fernando Wolford

My system: Preamp NAD C162, Acurus A250 Power, Klipsch R-610F After comparing with NAD I will use this one because it sounds a bit nicer. I would like to share my experience in the following way. I wanted more control for the high end and I'm happy with this 03 tube because it has more high end than the C162 (maybe it's because the C162 is old and not pumped up). I bought GE 5654W tubes for sound comparison and found no improvement over 6K4. I get a slightly thicker voice and slightly louder volume with 5654W, but that's not an improvement for me. There are both disadvantages and advantages. I hear an annoying popping noise when turning this preamp on/off. Turn on the power amp and turn off the power amp before turning off the preamp. There are red LEDs under the tubes and I hate to see that because it makes this preamp look fake. The right channel is louder than the left channel at very low volume, 23dB difference, e.g. 57dB versus 55dB. It is balanced when the volume is increased, the difference is less than 1dB, for example 65dB vs 64.5dB. I found this by playing a sine wave from YouTube. I can only turn the volume knob clockwise up to 20% because my 250w power amp is getting too loud. no problem for lower gain power amplifiers. I may change the potentiometer one day to fix the problem. Anyway, I like it very much.