When R2 is engaged does the treble shift push/pull have any effect on the sound or is it permanently engaged?
Lead off, R2 off = treble shift is switchable
Lead off, R2 on = treble shift auto-engages, is not switchable
Lead on, R2 off = treble shift is switchable
Lead on, R2 on = treble shift is switchable
I thought maybe this meant that pulling R2 doesn't do anything in lead mode and that the difference you hear is placebo since it's a very small difference but I can confirm it still works, if you turn the lead drive down to almost nothing, engage R2 you can hear a gain/tone change. This happens with treble shift both disengaged or engaged.
It could be the case! Blue stripes are massively aggressive from what I've heard. One thing on the IIC+ which IS definitely different regarding power compared to the III is that the V1 (first preamp stage), V3 (Lead/Reverb) and V4 (Lead/Reverb) all have a slightly lowered voltage rail going in (D+ on my schematic) which means lower plate voltage which I guess means slightly less break up so you'd maybe need to crank it a bit more? This is achieved with the addition of a 30uF 500V filter capacitor and a 1K resistor.
On the III but would involve fitting in another filter cap somewhere and cutting a few PCB traces and running some wires. You get this 'graininess' when treble shift if pulled in lead mode though right? It is basically just switching the tone stack caps from series to parallel, but maybe there's some kind of weird bleed through with the 360r and additional LDR?
I would be surprised if the 360r was the cause while I've still got all the III circuitry like R133 etc, it's certainly possible it's having an effect but I think most if not all is caused by the extra circuitry in the III and/or the voltage differences.
I'll probably mod my III to have this D+ voltage rail and see what happens when I get the chance. I've basically done all the other IIC+ things to it so can't harm to try! Mine doesn't have the grainy treble shift issue but then again I don't push Volume (labelled Volume 1 on mine) past 7 really... I will push it up to 9 or 10 and see if that makes a difference.
Do you still get the graininess on Treble Shift when in lead mode with Volume lowered to say 6 or 7 and Lead Gain cranked up higher to compensate?
It's mostly mitigated by turning down the volume and compensating with higher lead gain, or disabling treble shift and cranking the volume, but both of these approaches change the gain structure/sound fairly substantially. Higher lead gain loses punch and attack, and a disengaged treble shift makes the attack very spiky. I get closest to the sound I'm after with volume on 7 and the lead gain around 4 but this loses a lot of sustain and I have to play
very hard to get it to sound right, and I'm already a very hard player.
I'm pretty confident that removing the III circuitry will correct a lot if not all of this although I'd be interested to hear how changing the voltages sounds on your amp as that could be pretty illuminating. Like I said in the other thread I'm still thinking of going with simulclass values at c30 and maybe c27 but that's out of personal preference rather than to correct any issues. Once I've removed all the III-specific parts that could be having an effect I'll probably just be focusing on making the best III+ I can, it's always going to have its own thing going on by virtue of being a super 60W with the export transformer (out of interest, how would you describe the sound differences in yours between 60 and 100w?)