Three last questions guys.
1: As I look at the schematic for the 12au7 mod, I see that there are two 0.22uf caps in parallel with the 470uf caps. The 0.22uf caps are optional, and with such a little change in capacitance, I am wondering if it would be smarter to buy higher quality 470uf caps, or simply add in the 0.22uf capacitors and leave it alone.
2: Resistors R2 and R8 on the schematic are listed as 390K ohm resistors. However, on the BOM page, they are listed as 220K ohm resistors. Which one should I get?
3: Resistors R15 and R14 look like they just essentially lower the volume a bit. Is this true, or do they serve a greater purpose?
1. They are "supposed" to affect the sound quality, by using high end film caps you can get better sound. I quote "supposed to" because I don't have golden ears. I didn't bother using them on mine. Others argue that bypasses smear the sound.
3. They prevent oscillation. Kim's link explains it. It's the same for the mosfet gate stoppers. R3/R9.
Edit, when you wire it (assuming you don't have the PCB), put the stoppers right on or very close to the device. I put them right on the socket, and the mosfet pin.
Edited by holland - 8/7/13 at 3:31pm