I'm currently working through all the info I can find online as I'm preparing my Blue Stripe for a DIY III+ mod. It's taken a long time learning how to read schematics, looking at everything I can and calling Mike B to double check. There's a lot of info on the well-known C516, C30 and C27 mods, but little about the other component differences. There's also a lot of confusion because the only schematics for the III easily found are for the Red stripe, even when labelled as Blue.
One big myth is that the Blue Stripe is the same as the Red stripe minus the C30 mod. There are lots of component values that were changed between them. The Green and Blue stripes also have a different resistor alongside the C27 capacitor that is supposed to have as much if not more of an effect than the cap itself, which varied depending on the model from the IIC+ through to the Red Stripe. It's unclear whether or not C27 is 10 or 20pf in these, as simul-class amps were supposed to get 20pf. I've seen conflicting information, my gut says all greens are 20pf, all simulclass through to the reds were 20pf, 60/100w through to the reds were 10pf and blues are all 10pf but I don't know. Another IIC+ component I've only seen mentioned once online is the cap at C36 which works with the 5 band EQ.
I've updated Loylo's Red Stripe schematic with values I've been able to work out with my amp or find in others:
(typo at the unnamed pin cap in the lead circuit; should read 500pf for blue stripe value)
I think the 470k resistor listed above is R153. The R119 mod is one I saw on youtube that someone claims Mike B recommends, although I haven't been able to figure out what effect it has. That part of the amp doesn't appear to be on the schematic, but I may just be missing it. Two things I haven't been able to work out due to lack of schematics and my own knowledge deficit;
Someone with a green stripe said that the "phase inverter" cap on theirs was .1 rather than 0.47 as in the IIC+, however I don't know where to look for this. I'm guessing it's one of the big orange drop sprague ceramics but I can't figure out which cap he's referring to. There are a whole bunch of 0.47 and .1 caps around V5. He's not referring to C516 by the way, which is already a 0.47 in the Blue and Green Stripes onwards.
The 680k resistor after the lead input and LDR in the lead section I can't find for the life of me on my blue stripe. There's no 680k resistor in V3A or V3B when I look at my amp. I can see a 680k resistor near c506, which means it could be the 680k I'm after circuit-wise given c506's schematic proximity to the lead circuit but I'm not so sure, my ability to read these things is pretty rudimentary.
All that said, this took me quite a while to wrap my head around so if anyone else is looking for the Mark III+ mod and can't send it to Mesa to have it done, or just finds this interesting, hope this helps!
One big myth is that the Blue Stripe is the same as the Red stripe minus the C30 mod. There are lots of component values that were changed between them. The Green and Blue stripes also have a different resistor alongside the C27 capacitor that is supposed to have as much if not more of an effect than the cap itself, which varied depending on the model from the IIC+ through to the Red Stripe. It's unclear whether or not C27 is 10 or 20pf in these, as simul-class amps were supposed to get 20pf. I've seen conflicting information, my gut says all greens are 20pf, all simulclass through to the reds were 20pf, 60/100w through to the reds were 10pf and blues are all 10pf but I don't know. Another IIC+ component I've only seen mentioned once online is the cap at C36 which works with the 5 band EQ.
I've updated Loylo's Red Stripe schematic with values I've been able to work out with my amp or find in others:
(typo at the unnamed pin cap in the lead circuit; should read 500pf for blue stripe value)
I think the 470k resistor listed above is R153. The R119 mod is one I saw on youtube that someone claims Mike B recommends, although I haven't been able to figure out what effect it has. That part of the amp doesn't appear to be on the schematic, but I may just be missing it. Two things I haven't been able to work out due to lack of schematics and my own knowledge deficit;
Someone with a green stripe said that the "phase inverter" cap on theirs was .1 rather than 0.47 as in the IIC+, however I don't know where to look for this. I'm guessing it's one of the big orange drop sprague ceramics but I can't figure out which cap he's referring to. There are a whole bunch of 0.47 and .1 caps around V5. He's not referring to C516 by the way, which is already a 0.47 in the Blue and Green Stripes onwards.
The 680k resistor after the lead input and LDR in the lead section I can't find for the life of me on my blue stripe. There's no 680k resistor in V3A or V3B when I look at my amp. I can see a 680k resistor near c506, which means it could be the 680k I'm after circuit-wise given c506's schematic proximity to the lead circuit but I'm not so sure, my ability to read these things is pretty rudimentary.
All that said, this took me quite a while to wrap my head around so if anyone else is looking for the Mark III+ mod and can't send it to Mesa to have it done, or just finds this interesting, hope this helps!
