I thought the C30 values there were way off yeah.
Yeah that not to mention all the other differences between the different stripes with cap additions/removals and component value changes! The truth we can get out of it is that "From Red Stripes onwards an LDR was added (LDR6) to make sure Treble Shift is automatically engaged when R2 mode selected". That's ALL LDR6 is doing.
As for the LDR6 on RS onwards looks like something to remove if we want the R2 to be a switchable ++ mod rather than a third channel.
Well I don't have LDR6 and to get a switchable ++ mod as was on the 12 factory IIC++s (again unconfirmed this is what was actually on them but is highly likely) I need to do a load of extra work. By this you're talking about having C214 being switched on and off via a relay. Easy to do. But for a Mark III this developed so much further (not necessarily a bad thing) so there is R126 which needs to be bypassed as it currently adds more gain, I would add the 100K resistor between Treble and Volume Pots as recommended by Boogiebabies in conjunction with C214, change C214 to 10uF and balance it all overall using the R2 mod on R130. So A LOT of work and not really necessary? Also this has nothing to do with when it's in R1 mode or Lead mode without R2 pulled so changing the R2 channel is not going to fix the rest of your amp if you're unhappy with it. The switchable +/++ should be the least of your worries right now!
For anyone else following this we're currently theorizing that the hardwired IIC++ circuitry found in Mark IIIs R1 is partially to blame for this mushiness in transients, as are the C30 and C27 values
No I don't agree at all. I don't get this with my black stripe when stock - it sounded great from the beginning and others have confirmed this on here with theirs. I thought the whole point of this thread and the main problem you're having is that the Blue Stripes (and presumably Red and Green) have an issue when Treble Shift is pulled but when Treble Shift isn't pulled you can get pretty close to a IIC+? I'm just theorizing that LDR6 might have something to do with it! You need to disconnect the LDRs and put the treble shift on manually with some wire or something to bypass R128 - if your problem is still there it’s an issue with another part of the amp! It's trial and error testing not just 'I'll make everything like a IIC+ and the problem will go away' or 'this is definitely causing the issue'.
We also need to define what you mean by "hardwired IIC++ circuitry in Mark IIIs" - we're talking specifically about a 3.3M resistor and 250pF cap put around the 3.3M/10pF (20pF in simulclass). In the C++ this is a 2.2M and 20pF so is not "hardwired IIC++ circuitry" but something which developed from one of the versions of the ++ mod, was changed and became a part of the III.
You can remove these and see what happens. But AGAIN the whole point of doing any sort of work on this is that you should be changing one component at a time and via trial and error. I don't think these components really have any huge detrimental effect. To see the effect component value changes without trial and error you could try something like LiveSPICE which is an audio simulation. I'll be experimenting with this to see the effects raising/lowering component values has then go from there. This is about overall tone shaping though not a complete change of fundamental sound or 'feel' that the IIC+ is most famous for.
I know you don’t have the equipment to do the work yourself but you really do need to invest in some if you’re going to get into amp modding and trial and error with components. We’re basically redesigning the III which is fine but is a long and arduous process!! Anyway...
The famous Metallica tones were achieved with simulclass Mark IIC+ and IIC++ amps slaved into other poweramps. Simulclass amps had no C30 cap and C27 at 20pf in the preamp section which would have an effect on preamp attack, as far as I can tell 20pf would let more high end through before the lead stage, and C30 being omitted would let more through in the lead stage. The studio pre also appears to be 20pf here and I can't see anything corresponding to C30 on it either, could anyone confirm this? .
Try it out on something like LiveSPICE and see what happens
This whole Metallica IIC+ thing annoys me as well as some kind of mystery unobtainable sound, or that this is all that a IIC+ is good for. A Mark IV can do it fine and that's what they used on the Black Album I think. James used a Triaxis for most of the later live stuff. A lot of it comes down to recording setup EQ and stuff done in the studio. I've got all the recording notes for the two albums they used the C+ on along with a studio preamp and quad (from memory I think both were used) if you want here:
https://mega.nz/#F!bM5WxQrC!0Prq8cDM8VTuYm-H4S8geA
The poweramp effects the sound massively. The studio pre probably has 20pF and C30 removed because it was designed to be used with other mesa power amps which would have simulclass on them.
The studio pre is also at 15 rather than 2u2 on the polarised cap in the preamp stage coming off V3A. What difference to tone do these polarised caps make? There's still some confusion about their values in a IIC+ vs the various III stripes, which appear to have evolved across the series.
Not really. On a IIC+ they're .47uF on the cathodes for the preamp and reverb, with 15uf or 22uF on the cathodes for the pull switches (from photos I've seen both used and makes a very minor difference). 2.2uF on V3A and .22uF for the pull bright on the lead circuit (normally a military spec Kemet). The studio pre is not a IIC+ but is quite similar in a lot of ways.