Newbie problems with startup!

[Matt J]

So I've been doing some more diagnostic work and think I've found the problem.
I do not think it is anything inside the amp, it's something with the Dr. Z Airbrake I'm using. I picked it up off of Ebay a few months ago.

The other day I took the amp outside and cranked it up some. I did not notice the staticy/overloaded sound I have been describing. I have a Weber Mini Mass attenuator I used with my 18watt amp and decided as an experiment to try it out with the Express. It brought the volume down without there being the overloaded sound. This is not a long term solution though. The Weber Mini Mass is only rated for 25watts and it only took a few minutes before I noticed a burning smell and the attenuator seemed to be overheated. I have not used it since then. I plugged back in the Airbrake and overloaded sound was still there. Has anyone had anything like this happen to them? I am going to put this in its own forum.

Now it is time to seriously start tweaking the amp. I still want to get a little more headroom out of it and clean it up a little because it is a tad harsh as it sounds. What would some of you recommend I start looking to adjust first? Looking at the BOM it suggests changing the values of one of the bias resistors. R29 would go from 220k to 150k any ideas on how this would affect the tone? Also, if I changed C12 the PI stability capacitor from 47pf to 100pf or 200pf how would this change things?

Two of the pots where a little rough turning and scratchy, so I'm going ahead and replacing them with PEC versions. I'm lowering the values of the bright switch caps too since the amp is very bright naturally as it is.

Thanks again for all the help and advice you have all been giving me on this!

- Matt J.

[KellyBass]

Sometimes with (these amps in particular), It's not so much changing the VALUE of component as it is the TYPE of component. For example with one of mine, switching the 500pf treble cap from a silver mica to a polystyrene cap of the same value, made a HUGE difference in the overall stability of the amp. It's a blast to solder in different parts and give a listen. Endless combinations...