Well, I've had the SP-14 in the system long enough to give an updated comparison.
Thanks for the write up.
The SP14 uses 6SN7s?
Just curious which version and whether you tried others.
I had an SP13 years ago (I think the first, maybe one of the prototypes).
I think basically a 6CG7 version of that.
Please let us know if you think the sound evolves (?) More
Yes, the SP14 uses 6SN7s and a 6X5GT rectifier tube. I've tried the modern day Tung-Sols and the Electro Harmonics for the 6SN7s, I prefer the Tung-Sols over the EH, although I only gave the EH a couple of days before going back to the Tung-Sols. The Tung-Sols started sounding quite good after about 3 days. I went back to the EH for a while but they do not sound nearly as good as the Tung Sols in this circuit. I have some NOS tubes coming from Upscale Audio soon, so it will be interesting to hear them.
Regarding the rectifier tube, I tried both a NOS Sylvania 6X5GT-G and a NOS Tung-Sol 6X5GT. I had read good things about the NOS Tung-Sol, but in this circuit it sounded dull compared to the Sylvania.
Regarding an updated comparison between the SP14 and the Masterpiece, they both sound very, very good. Ultimately I prefer the SP-14 overall. I can get them both to sound great or not so great depending on the tubes used, but to get the best sound out of the Masterpiece, I have to sacrifice low-end weight, most likely based on tube choice (not just compared to the SP-14, but other preamps as well). The SP-14 has a nice solid foundation, and an extra touch of tube-y richness that is very engaging. Please note that I am not using the standard coupling capacitors that come with either design.
Both preamps measure very well, with extremely low distortion for tube designs. The measurements run very similar between the two units, except the SP-14 has a 9dB better stereo cross-talk measurement.
I think most people would be happy with either preamp, so I'll write a bit about the building experience of the two.
The Masterpiece comes with much better directions than the SP-14. The directions for the Masterpiece are excellent, in fact. I was eventually able to get reasonably good directions for the SP-14, but there are a couple of versions of directions floating about that conflict somewhat with each other. I think the designer of the SP-14 could do better at compiling a definitive set of directions for whatever version of the preamp and volume control he is selling.
That being said, the SP-14 is definitely easier to build than the Masterpiece. The Masterpiece is all point to point wiring using terminal lugs, and often many components are soldered to a single terminal. There is not a heck of a lot of space around the small tube sockets, so one must take care that no components or wires are touching things they shouldn't be touching. The SP-14 circuit board makes for an easier build. I did find myself buying a couple of extra components to make the SP-14 build a little easier and cleaner; things like little junction boxes for all of the wires that need to be joined to the IEC terminal. I recall that four wires needed to be soldered to a couple of the IEC terminals, so I bought a couple of five way universal wire junctions which helped a lot. If you want to experiment with different output coupling capacitors, I would also recommend something similar to fast-on wire connectors that can be soldered in to the circuit board where the transformer wires connect, so the wires can be easily removed to lift the circuit board. Otherwise you have to either unsolder the wires, or leave the transformer leads longer and coiled out of the way.
Other thoughts: the volume control and the input switch that ship with the Masterpiece, even if they may not effect the sound quality, are extremely cheap feeling. I would swap these out just for the tactile feel alone. When you build something, why would you want it to feel cheap? That said, a high quality stepped attenuator is not inexpensive.
One advantage of the SP-14 is the ease of integrating a remote controlled volume control. I love the SP-14 optional Khozmo 64 steo relay based controller. It comes with a digital display, a very nice feeling aluminum remote control which does volume, mute, input switching, and dimming of the display board.
I get the feeling that the designer of the SP-14 offers options (like the volume control) without fully implementing them on his own first. As I said, I love the volume control, but there were a couple of issues. First, the ribbon cable between the control knob and the display circuit board was too short to reach the distance where these are installed in the SP-14 chassis. I think the designer would have knows this if he had built the unit with the optional component himself beforehand. I struggled with hum for a number of weeks, because the way I had the volume control relay board grounded was causing a bit of a ground loop. The designer mentioned he hadn't yet figured out the optimal relay board grounding, so I first implemented it in the manner the board offered with a ground connection for each input. After thinking about that for a while, I removed all of those ground connections, because the relay board had a ground connection to the main SP-14 circuit board, and that had its own connection to the ground terminal buss wire. Removing those extra ground points at the inputs lessened the hum to the point where it is inconsequential. This is the kind of advice I feel the designer should be giving the customers, as opposed to the customer experimenting and giving advice back to the designer. The Masterpiece is clearly a fully vetted design as shipped, with clear instructions.
Still, all is well that ends well, and I am extremely happy with the performance I am now getting out of the SP-14.
I've attached a crappy (sorry) picture of both preamps side by side.