I've had this thingy for couple years now and ever really had any use for it. Then, couple weeks ago, I bought active speakers and realized I need a preamp for those (well, at least volume control). Then I remembered this one.
First of all, I thought I'll do some measurements and maybe improvements for it, because I wanted to be sure it works like it should be. You never know about these cheap chinese thingys..
Well, frequency response measurement was a real disappointment. I measured -5dB at 20Hz. Definitely not acceptable.
I replaced all those 0.47uF caps with 2.2uF caps. Much better now, thank you.
Then, I wanted volume control at the input (where it really should be). I took the original volume pot away and put some 47k resistors instead, from + to GND.
Then, at the input, sucked those 10k SMD resistors off and put 470k resistors instead, from + to GND. This ensures high input impedance.
Then, volume pot in front of all that.
Finally, I measured some other things too; maximum gain 9dB (enough, at least for my purposes), noise level -99.6dB (more than enough) and THD 0.045% (good for tube machine).
I think I could live with this thing now. (Maybe I'll change those underrated filter caps, but yeah..)
