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PostPosted: Mon Apr 02, 2018 12:42 pm 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
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After spending time with my Mark III+ I've found that it sounds much closer to a IIC+ with the treble pull shift not engaged. When it's engaged the transients get very mushy and the distortion takes on that Mark III character as opposed to the smooth gain of a IIC+. The schematics look exactly the same for both, does anybody know what might be causing this? It doesn't sound faulty to me at all, it just changes the character of the gain in a major way. Could it be something to do with the R2 channel?

I've heard the same difference in the Mark III and Mark IIC+ modes on a Triaxis, though less pronounced. As that's got a totally different pcb layout I don't want to just attribute it to the pcb being different. My Mark III+ mod was all done with metal film resistors but I hear the same characteristics on Mike B-done Mark IIIs online, and as far as I know he uses carbon films or comps. I also don't see this being the case with the Triaxis Mark III as gutshots from them seem all carbon film based and they still get the III sound down.


Last edited by lions on Mon Apr 02, 2018 4:59 pm, edited 1 time in total.

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PostPosted: Mon Apr 02, 2018 3:42 pm 
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Mark I

Joined: Mon Dec 08, 2014 2:00 am
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Yes I am with you in this opinion , when it is not pulled it is better , more full tone like the IIC+ , I am using a pair of tungsol 5881 in power tube section and 4 tungsol 12AX7 Gold pins from v1 to v4 and the PI I use tungsol 12AT7. Sounds pretty great with this setup


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PostPosted: Mon Apr 02, 2018 4:56 pm 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
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How does the AT7 change the sound on yours?


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PostPosted: Tue Apr 03, 2018 12:06 am 
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Mark I

Joined: Mon Dec 08, 2014 2:00 am
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12AT7 will make the amp another beast , it will tame some harshness without affecting its aggression, will give it a bold 3D character with more bottom dynamics. I have tried many 12AT7 tubes like JJ Gold pins, Genalex gold lion gold pins , but the best was the tungsol 12AT7 in the PI.


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PostPosted: Tue Apr 03, 2018 8:43 am 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
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Thanks for the info!

The Quad Preamp says the treble shift on the IIC and III modes is voiced differently:

Image

I'll try to compare schematics and see what might be causing the difference.


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PostPosted: Wed Apr 04, 2018 7:35 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 101
Quote:
After spending time with my Mark III+ I've found that it sounds much closer to a IIC+ with the treble pull shift not engaged. When it's engaged the transients get very mushy and the distortion takes on that Mark III character as opposed to the smooth gain of a IIC+. The schematics look exactly the same for both, does anybody know what might be causing this? It doesn't sound faulty to me at all, it just changes the character of the gain in a major way. Could it be something to do with the R2 channel?


Check out the power sections between the two. That's where the treble shift LDR gets power.

They're different due to the R2 slightly. Main difference is that there are 2 more LDRs added for the R2 channel, plus an extra diode and resistor and for 'RHY 2 LEVEL ATTENUATOR', and there is a whole addition of a 6V DC supply for the R2 relay off the heater supply. I'm not a wizard in electronics to know what effect it would have though but seems a good place to start.


Last edited by jrb32 on Thu Apr 12, 2018 5:52 am, edited 1 time in total.

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PostPosted: Fri Apr 06, 2018 7:57 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
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Quote:
The Quad Preamp says the treble shift on the IIC and III modes is voiced differently:


TREBLE SHIFT on the Quad = TREBLE SHIFT on the IIC+/III for Channel 1. The LDR layout controls the fact that you can't have treble shift for the Rhythm Channel but you can for the Lead Channel. On Channel 2 they've made it a simple switch it seems so it is present on both Rhythm and Lead for Channel 2.

The LDR switching is a nightmare on the quad so good luck comparing the two! I don't notice the graininess you mention unless you're talking about a background noise of the amp? That increases on my III Black Stripe slightly but apart from that I don't have what you describe.

Channel 1 and Channel 2 on the Quad also have tone stacks that are voiced differently where the TREBLE SHIFT occurs, as well as some other differences between the two.

One other difference is that Channel 2 on the Quad adds a 3.3M and a 180pF to the classic 3.3M/10pf where the Lead channel Enters/Exits that is not dissimilar to the III. Perhaps this is deliberate to distinguish the two? To say Channel 1 = IIC+ and Channel III is incorrect though but they are loosely based on their preamps and lead circuits it seems. From what the manual says Channel 1 has a treble shift voiced like a III so that's a bit opposite as well!


Last edited by jrb32 on Tue Apr 24, 2018 10:43 am, edited 4 times in total.

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PostPosted: Fri Apr 06, 2018 8:17 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 101
charleonthronez wrote:
I am using a pair of tungsol 5881 in power tube section


Remember Mesa use a fixed bias in their amps for output valves! This means you can't safely use ANY output valves without re-biasing the amp or at least checking the bias is within tolerance. This requires some decent kit or expertise to do so as you're dealing with some serious voltages!

Saying that I think Mesa basically take Sovtek or other brand tubes, keep the ones that are within tolerance and rebrand them, then sell on/back the ones which aren't. But this is something you should be checking - if not go Mesa output valves as you can guarantee they're correct and won't cause any issues.

Just a word of warning! I'm sure it's fine but better to check and be safe.


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PostPosted: Tue Apr 24, 2018 10:30 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 101
OK so quick update after messaging lions on here. We've established that there IS something weird going on with the Treble Shift on Mark IIIs from the Red Stripes onward (I think this is board CP1G but I'm basing this off a green stripe) where there is an added LDR stacked over LDR1 for the Treble Shift, a 360 Ohm Resistor added and a diode which seems to be connected to the R2 channel as well (as listed in the loylo schematic). Why this is and whether this can be removed is still being looked into.

My Black Stripe has the CP1E board and has the treble shift the same as a IIC+ and on the III schematic. I think the Purple has the same CP1E board but need someone to verify this.

This could explain the treble shift 'voicing' in the Quad on Channel 1?


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PostPosted: Tue Apr 24, 2018 10:49 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
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Quote:
This could explain the treble shift 'voicing' in the Quad on Channel 1?


Actually on second thoughts this 'voicing' is done by the tone stack capacitors it would seem, probably nothing to do with the added 360 Ohm Resistor and LDR in the later IIIs?


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PostPosted: Wed Apr 25, 2018 12:45 pm 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 63
Found this, not sure if all the info is correct but it might help.

Restless Rocks wrote:
Just going from memory, as I have not documented any of this stuff on paper;

The "no stripe" black dot black plus: This is the one with the original CP-30 PCB ( this is by memory remember so I may get some of the numbers a little wrong) which is pretty much like the published schematic. The major differences in the stripes concern the R2 circuit. The R2 circuit in the black dot is just like the schematic. and C30 was 500pf in the lead circuit.

The "Purple stipe" Saw a redesigned PCB, the CP-31 (I think) Here were the major changes to the R2 circuit: There was another LDR added which switched in a .47uf cap on the cathode of V2a giving it more gain. The tone stack was lifted, via the relay, (this is unique only to the purple stripe and reminesent of the original MkI "pull boost") this also adds a little more gain hitting V1b but gives the R2 of the purple stripe more of a blurry feel. C30 was also 500pf in the purple.

The "Red Stripe" saw C30 return to the 1000pf cap like the C+. The R2 was restructured basically by using the relay leg to kick in the 750uf cap on top of the tone stack instead of "lifting" the stack by un-grounding the mid control. This is like the "pull shift" of the lead circuit kick in automatically for the R2 giving it a much more focused mid feel.

The "Blue Stripe" remove the C30 cap altogether, giving it the most raw and aggressive lead. IIRC the 120pf was put across the grid and cathode of V2b (ala C+) to tame some of this. The power supply voltages to the preamp stages were manipulated on some by changing the resistors between nodes A, B and C.

The "Green Stripe" of course is "basically" a Blue with Pentode wiring on the simul output pair. A few very subtle changes in cathode caps and tone bleed caps which are becoming esoteric at this point. Mostly to compensate for the also subtle variation in production tubes available at given times.

Hope this is of some help, again this is all from memory and subject to error.


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PostPosted: Thu Apr 26, 2018 6:52 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 101
Quote:
The "no stripe" black dot black plus: This is the one with the original CP-30 PCB ( this is by memory remember so I may get some of the numbers a little wrong) which is pretty much like the published schematic. The major differences in the stripes concern the R2 circuit. The R2 circuit in the black dot is just like the schematic. and C30 was 500pf in the lead circuit.


My Black Stripe 100W is from Jan 1986 so not one of the very very first ones but still fairly early and has a 163XX serial number with the board CP1E Copyright 1984. The R2 circuit engages R130 at 6.8K with one LDR and C214 a .47uF cap on the cathode of V2A with a second LDR. C30 is 2000pF not 500pF. It is possible the first Black Stripes has only the R130 added like in the original schematic but I'm not sure what effect that would have, plus I think the .47uF cap or at least some cap on the cathode of V2A is key to the gain on the R2 channel with it being similar to the switchable factory +/++ models? I also found another person on here who wrote about their 166XX Black Stripe having the CP1E board with the two LDRs for R2 and .47uF cap. It would be very odd for the PCB board to change within the first 9 months of production, plus having a 1984 copyright date so I'm not convinced by this.

Quote:
The "Purple stipe" Saw a redesigned PCB, the CP-31 (I think) Here were the major changes to the R2 circuit: There was another LDR added which switched in a .47uf cap on the cathode of V2a giving it more gain. The tone stack was lifted, via the relay, (this is unique only to the purple stripe and reminesent of the original MkI "pull boost") this also adds a little more gain hitting V1b but gives the R2 of the purple stripe more of a blurry feel. C30 was also 500pf in the purple.


Again the PCB I think is the same at the Black Stripe. The difference between the Black and Purple stripes is due to some component value changes such as in the lead circuit I thought? C30 is also 2000pF not 500pF in the purple stripe. I think the tone stack being lifted is what the R126 resistor is for when R2 is engaged (the 'gain boost' does this feature in the Mark II). But again I have this in my Black Stripe so unless they did a very early production run before changing the board layout I'm pretty confident the black and purple stripes have the same board and same R2 channel.

Quote:
The "Red Stripe" saw C30 return to the 1000pf cap like the C+. The R2 was restructured basically by using the relay leg to kick in the 750uf cap on top of the tone stack instead of "lifting" the stack by un-grounding the mid control. This is like the "pull shift" of the lead circuit kick in automatically for the R2 giving it a much more focused mid feel.


Again incorrect as C30 is 500pF in the Red Stripe. Cool so If the un-grounding thing is the case then R126 should NOT be present on the Red, Blue or Green stripes? Can you confirm this?

Also if we assume the LDRs are like a switch, then LDR6 in the Red Stripe (according to the loylo schematic) basically engages treble shift automatically on the R2 channel. That makes sense with the information available and why there was a design change in adding the additional LDR around the tone stack LDR on the Red Stripes onward. This should be able to be removed if needed I would think.

I'm also sure this is where the PCB redesign came in, adding an LDR, D212 and a 360Ohm Resistor on top/next to the Treble Shift LDR1

Quote:
The "Blue Stripe" remove the C30 cap altogether, giving it the most raw and aggressive lead. IIRC the 120pf was put across the grid and cathode of V2b (ala C+) to tame some of this. The power supply voltages to the preamp stages were manipulated on some by changing the resistors between nodes A, B and C.


Incorrect as C30 is 1000pF in a 60W non reverb. Could you confirm there's a 120pF cap across V2B on your blue stripe?

Quote:
The "Green Stripe" of course is "basically" a Blue with Pentode wiring on the simul output pair. A few very subtle changes in cathode caps and tone bleed caps which are becoming esoteric at this point. Mostly to compensate for the also subtle variation in production tubes available at given times.


I think the Green Stripe has some component differences still between a blue as it's not as aggressive but could be wrong. For example I thought it had a 3.3M resistor on R106 instead of the 2.2M like in the Blue? I know Green does have pentode wiring though on the output valves from all the info I've read though.

That helps solve the mystery around the R2 channel redesign though. I would need to confirm but makes the most sense. Thanks :)


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PostPosted: Thu Apr 26, 2018 5:16 pm 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 63
I thought the C30 values there were way off yeah. The rest seems to make sense. I think the GS are the same as the BS apart from pentode wiring and a few cap differences later in the preamp/poweramp to compensate for the difference in tone that causes.

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.

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. 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?

I wonder if anyone knows how much the poweramp section affects the slave out as opposed to the preamp out? Anyone able to confirm the 20pf as letting more highs through than 10pf? 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.


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PostPosted: Fri Apr 27, 2018 6:57 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 101
Quote:
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.

Quote:
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!

Quote:
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...

Quote:
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.

Quote:
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.


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PostPosted: Fri Apr 27, 2018 1:39 pm 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 63
Quote:
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!


I was thinking more the extra 360r resistor as well as R126. I have no use for the R2 channel at all, so having it as a switchable ++ mod would be the only use I'd ever get out of it!

Quote:
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'.


As far as I can tell the reason treble shift unpulled is getting me closer to the sound I'm after is having it pulled lets more low end through the preamp which makes the transients less tight. Allowing more high end through at various stages here would have the reverse effect, especially before the lead stage, as this would affect the response of the amp as much as it would the overall tone.

The studio pre and simulclass preamps are set up without the C30 and 20pf as are the blue stripe, green stripe and to a lesser extent red stripe with the 500pf C30.

There may well be something weird going on with the treble pull shift due to the relay switching and 360r/R126. It may be the result of the extra 3M3r/250pf capacitor in the III. It also may be due to C27 and C30 values. I think it 's a combination of all of them, hopefully not LDR6 though.

Quote:
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.


I'm referring to R133 and C28.

Quote:
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:


I don't think a ballpark tone is unobtainable at all, it's easily achieved with a C+ and you can get close with a III, but every III I've heard has a slightly different vibe going on. I'm not trying to recreate a C+ for the sake of it, or the Metallica sound (which would be pointless as they used different gear on every album) but I'm trying to get a particular sound out of mine that has something in common with both though and seems to be a mostly preamp-governed difference. A red and blue stripe, both with lower or deleted C30 gets you close but they both, the Blue especially, have a different tonal character due to all the other component changes. So for me with the III+ mod, I know the IIC+ gets the sound, so I'm shooting for that first, and then working from there.

Mike B's opinion when I spoke to him was that Mark IIIs were deliberately voiced differently and that they can be modified to be identical on a scope but not in feel (transformers etc). It's also likely given what we've found that the first version of the IIC++ mod is already wired into IIIs with R133 and C28. This mod on the IIC+ is by all accounts a voicing change as much as it is a gain structure change, adding low mids/upper lows, which is completely consistent with how my III feels.

Quote:
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.


I'm asking how the poweramp affects the slave/direct out specifically. Is it more like an extra speaker out, or is it more like an fx loop out but after the 5 band?


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