Added a gain stage to my 18 watt Lite. Works great, except for...

[Tyrannocaster]

I have a stock 18 Watt Lite 2B amp. On a whim I added the gain stage from Doug's Stout amp. I made sure the cathode bypass resistors on both triodes were his value (before, they were tied together and used a lower value, naturally) and I have checked the wiring over and I believe it's okay. In fact, the amp sounds great. Except that I can't turn it all the way down now without getting a loud grinding/static/buzz/whatever noise. I measured the volume pot's resistance at the point this sound kicks in and it is at about 240 ohms. Something in the new circuit has changed a ground circuit, I guess? I put a 470 ohm resistor between the pot and ground temporarily so I won't accidentally turn it down all the way while testing (I want to keep my speakers but really it's just so shockingly annoying that I don't want to hear it) but that's obviously not a permanent fix, although it does make the amp livable in the short term. Since I have looked the wiring over and don't think I made any mistakes I am thinking it's either lead dress or (more likely) there is a mistake that I am not seeing. I thought I'd ask what might be a cause of this kind of problem since I've never encountered this one before with my limited experience.

I must say that the second stage adds a lot to the amp's playability. I like this amp but my one complaint has always been its lack of gain. It was great for early Kinks type stuff but for real drive I had to use a pedal. Now I can do both by just rolling my guitar's volume down. Cool.

EDIT: Forgot to add that I didn't use the relay - I just added the gain stage as per his NO RELAY schematic.

[Tyrannocaster]

Well, i just wasted the entire weekend on this and I feel grateful that I was able to get it back to stock shape so at least I didn't lose ground. I tried everything I could think of, including rewiring the whole preamp, checking the schematic as I went, and the volume control just gave me fits with the weird buzzy, crackly noises when I turned it down. Finally I just took out everything I did and after a lot of work got it back to a stock 18 Watt Lite II. I liked the overdrive tones a lot but they weren't worth the noise (and even radio stations once!) and instability issues that arose. I guess I would have to build it from scratch with the idea of using two gain stages, although my build is so sparse it was easy to put the extra one in.

Oh well. I wish I could say I learned something from this but all I learned was that I couldn't pull this off and I haven't any idea why. Still trying to find the bright side of that...think I need a break from this.

[Tyrannocaster]

Success of a sort. I tried again, making sure all new wires were shielded and routing them carefully as I could, and moving some of the original amp's wiring around to make things cleaner. This time I'm not getting those noises although I did get some at first and seemed to be able to stop them by moving the input wire to V1B - I can't imagine why that made a difference (if it wasn't coincidence) so I still haven't put the back in its cabinet and am playing it a lot just to see if it comes back. But I did put a clamp on that wire to keep it from moving out of place and so far it's okay.

The amp has a ton of gain; in fact, I tried a 12AU7 instead of the standard 12AX7 for the two triodes and it STILL has enough. IMO, you only need so much, and any more is wasted. The amp has a GREAT clean-but-ever-so-slightly-fuzzy quality when you roll the treble down on the guitar - I wish I knew how to get that as a feature! With the tone up on the guitar but the guitar's volume down it sounds like a razor (in a good way - not distorted, but, well, just good) and then when you turn the guitar up the distortion kicks in incrementally. It's really important to have the right bright cap on your guitar volume pot for this setup, that's for sure.

There is somewhat more hum than there was before, although not until you crank the amp up. The hum is always far, far below the roar of the amp so it would work for recording or live purposes fine. At low volumes there isn't any hum at all so I'm not going to spend time trying to find it.

These 18 watters are so much fun; they are loud and they sound really, really good. But now this one is much more versatile than it had been. I am just hoping I solved the awful buzz/pop/crackle/RiceKrispy sound; so far so good, but I'll wait and see what happens over the next few days. By now I'm almost willing to be it will be back...but I also believe in the magic of crossed fingers.