Originally Posted by scompton
I want to make sure I have the right idea of the zener tweak. You replace the resistor R4P with a zener, correct? I didn't get one with my kit so I'll have to order one. On Mouser there's 14,000 options for zener diodes. What specs does it need to have?
I socketed R4 in my build and tried a few 1/2W 18V zener (1N5248) from Digikey (Fairchild, Diode Inc, On Semi...). The less noisy, and less expensive too, of the bunch were the Fairchild. But there was still some noise (faint background hiss) that could be hear on low volume musical passage. I installed back the 18K resistors.
I admit I didn't play with the tail current so maybe the noise would have gone with higher tail current. If I had only heard the SOHA II without the resistors, I would had probably be very happy with the zeners, the hiss was not very intrusive.
Edit: I forgot what Runeight said below, install the zener in the right orientation. This is the most important advice