I apologize in advance if this has been covered already, I couldn't find it.
I've noticed (as others have) that the the Express starts to break up at around 9:00 and the sweet spot is around 1:00. I measure the resistance at 1:00 to be around 120K for my pot.
I'd like to try a 250K volume control for more quiet range. Will this have any undesirable effect? Is anyone using a different value for the volume pot?
Would like to know if that 1M is critical, that ground buss on the back of the control will not make for a quick and easy swap.
I might just tack a 330K or so resistor across the pot first to see how it sound before making the change.
The 1M pot actually has two functions: as a voltage divider input to V1b and as the load for the tone stack. Changing it won''t affect V1b (although I don't think it will work the way you want it to because you will have replaced the 880k "dropping" resistance in front of your 120K load resistance with only 130K dropping resistance -- you'll have to turn down to 30K to get (sort of) the same reduction. More significant is that going to 250k will whack 6-10dB off your mids and low-mids and make the amp incredibly bright.
You could try putting a 500K resistor in series with the input leg of a 500K pot. Full up you'll still only be at 50% of what you have with the 1M pot.
Actually, I'm interested in the effect of manipulating the whole tone stack: Marshall values, Fender values, maybe a modified Baxandall. When I get around to it, I'll post what I discover.
From what you are describing it sounds like you would benefit from a split load plate resistor ala' Komet's fast gradual switch. Another option would be to replace the first 1meg resistor in the PI with a 1meg pot to dial down some of the gain and improve the range. A third option would be to upgrade the volume pot in your guitar's with a more gradual taper.
Others can comment on the split load's effectiveness but I really liked the MV option I suggested above. Good Luck with tweaking!
