Question for people who have used "real hifi" and expensive pre-amps? How "bad" is FX-03 (when modded including a decent psu, quality capacitors, etc) compared to the high quality preamps? Or is it in some cases, just the brand name what makes the cost high?
The FX-03 is a very good preamp. It's just that it uses fewer parts than more expensive "regular" preamps and has fewer features. That's probably what helps it sound good. I have done the bigger power supply and tube swap and if it had multiple inputs, including a phono, and a remote it would find a semi permanent place in my system.
Well, I would say that it's a "very good preamp
for the money" because in that price range it's (and it's cousins) pretty much the "only game in town". Its main value, as I see it, is that it's a
fantastic introduction to the world of tubes.
It's biggest limitation is that it operates the tubes at ridiculously low voltages that are nowhere close to what the tube data sheets recommend.
When I was breadboarding my preamp project I tried the ones used in the FX. The basic circuit design I use is exactly the same as the FX uses, it's called an anode follower.
As I've said before, I was surprised that they sounded as good as they did when operated at the stock FX voltages, which are nowhere close to what the tube data sheet recommends. I also tried them at "normal" voltages and, not surprisingly, they sounded much better like that.
Earlier in the thread, I posted two schematics that operate the FX tubes at those higher voltages. Unfortunately, the FX can't simply be modded to run them at normal voltages.
During the breadboarding process I ended up experimenting with maybe 10 or 12 different types of tubes. Not variations of the (tube rolling) types used in the FX but totally different types of tubes. With the exception of the ones used in the FX, they were all chosen because they had low gain and low output impedance.
Low gain because modern amps can typically be driven to full power by a line level source alone, so no gain is actually
needed. Excessive gain just creates problems, as discussed in the posts above about volume control issues. And it all just gets dumped to ground in the end.
Low output impedance because it allows for a better impedance match with a SS or Class D amp. I wanted to be able to use the preamp with my Yamaha M-60 SS power amp. I really just tried the FX tubes out of curiosity since they are not low gain and the output impedance of the FX is not particularly low. Many preamps add a cathode follower stage, using an additional tube, in order to lower output impedance. I just used a tube that has lower impedance and kept the circuit simple.
YMMV, of course, but the tubes used in the FX rated at the bottom of my list, even when run at normal voltages. I only found one that I liked less (the 1LE3) but that was totally due to its microphonics - simply rubbing my finger over the surface of the volume knob could be heard through the speakers! Other than the microphonics, it actually sounded quite good.
Most of the people who are fans of the FX have little to no experience with other tube preamps or tubes in general. But, as I said earlier, it's a great
introduction to the world of tubes. If you expand your horizons you'll find that there are many other options, especially if you learn to DIY.
The tube I ended up using in my preamp, which I call the Boogie Factor, is the 1626. Here's a thread about it:
https://www.audiokarma.org/forums/index.php?threads/1626-preamp-build.931276/
And, if the taste of tubes you've gotten from the FX appeals to you, you really should try a tube amp. I've found that a tube preamp does improve the sound of SS amps but it's a combo that only gets you, maybe, 20% or so of the full "tube sound".
I obviously prefer all tube, although I have and use SS and Class D too. As with anything audio, YMMV and others may prefer SS.
Basically linear psu are everywhere, thrift stores, flea markets... 2nd hand are cheap if not maded for "audio" market.
The KISS principle.
