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Mark IIC+ Schematic (correct!)

Posted: Tue Feb 20, 2018 8:41 am
by jrb32
Hi Guys,

I was so annoyed with all the misinformation out there that I've drawn up an accurate IIC+ schematic of the main sections. This includes information I can find regarding the ++ mods. This is taken from info I can find on here from chipaudette who had an RP10A IIC converted to a IIC+ by Mike B and all the great IIC+ info from Boogiebabies that's on here. Thanks so much for this info! I also bought an RP10A IIC later which was then upgraded to a IIC+ and can confirm everything is accurate as possible and traced for the RP10A. I've also seen enough photos of other IIC+s (RP11A, SP11A) to know that they all end up the same circuit wise.

Anyway the schematic is here. Hope it's of use to someone!

IIC+ Schematic: https://drive.google.com/open?id=1ieTnM ... RIDwbLAcUQ

Enjoy!

Re: Mark IIC+ Schematic (correct!)

Posted: Tue Feb 20, 2018 12:51 pm
by jediguitarist
Wow. Great work! I wish I even remotely knew what any of that means. Hahha.

Would be awesome to be able to troubleshoot my amps instead of just changing tubes and hoping that fixes the problem. :lol:

Re: Mark IIC+ Schematic (correct!)

Posted: Thu Feb 22, 2018 9:59 am
by tony777
Awesome!!!!

Re: Mark IIC+ Schematic (correct!)

Posted: Fri Feb 23, 2018 12:03 am
by lions
This was really useful for me for comparing my Mark III for the + mod!

The 100k resistor after the volume you've labelled as optional, is that for the ++ mod? It's not on the other schematics I've seen or anything for the Mark IIIs.

Re: Mark IIC+ Schematic (correct!)

Posted: Fri Feb 23, 2018 7:54 am
by jrb32
The 100k resistor after the volume you've labelled as optional, is that for the ++ mod? It's not on the other schematics I've seen or anything for the Mark IIIs.
It's a remnant of upgrading a IIC to a IIC+ that Mike B leaves in when upgrading a non factory IIC to a IIC+. Info I got was from here: http://forum.grailtone.com/viewtopic.ph ... 49&start=0

This 'fire breathing dragon' thing is not a ++ mod or something offered by the factory. However, it adds in even more gain when combined with a ++ mod. A simple switchable gain boost is to add the 100k resistor between the pots and then make the 15uF off V2B switchable via a push/pull middle pot and/or via a simple footswitch. Anything more than that and you've got to add in a relay.

Re: Mark IIC+ Schematic (correct!)

Posted: Thu Apr 12, 2018 7:34 am
by jrb32
Link updated to include info on the ++ Mod. There seem to be two versions so have included both. One involves a component addition and the other includes adding a relay to switch similar to the Mark III.

https://drive.google.com/open?id=1ieTnM ... RIDwbLAcUQ (same as link above - updated that as well)

Re: Mark IIC+ Schematic (correct!)

Posted: Wed Dec 12, 2018 12:09 pm
by jrb32
100% confirmed with an RP10 IIC that was upgraded to a IIC+. Links updated to correct version.

Enjoy!

Re: Mark IIC+ Schematic (correct!)

Posted: Thu Jan 24, 2019 6:11 pm
by woodbutcher65
Cool stuff, thanks for doing it.

Now...as I understand it, a IIC+ can have either the RP10 or RP11 preamp board in it.

Are the differences between these two preamp board understood? And how will the difference affect tone?

Re: Mark IIC+ Schematic (correct!)

Posted: Fri Jan 25, 2019 6:40 am
by jrb32
Now...as I understand it, a IIC+ can have either the RP10 or RP11 preamp board in it.
Or the SP10A or SP11A for Non Reverb (RP boards - the R stands for Reverb). Read the IIC+ guide for dummies on here...

I haven't done a layout for the RP11A board or the SP10A or SP11A board. Since no two IIC+s sound the same you'll be hard pushed to understand the differences tone wise. From a circuit point of view the only difference I can tell is that C9 and R105 are swapped over in the RP11A and SP11A board so that C9 comes first off V2B. Apart from that, identical circuit wise. Layout slightly different.

The RP11A and SP11A boards were designed for the later IIC. This IIC appears to have a few features from the IIC+ (e.g. quick glance a 10M resistor for the treble shift). It was designed in mind to make it an easier upgrade to a C+.

From the guide for dummies:
The RP-10A is based in the style of the IIB with LDR's for switching instead of the one relay. The RP-11A is the circuit board that was
redesigned for the IIC with a much different layout. It was also later the board used in the IIC+ with many component changes and
a different circuit layout. From what I could find out about the RP-10A, it was the early production IIC PCB. It was changed somewhere in the mid range
to the RP-11 in mid to late 1983. Hence, both boards have 1983 copyrights.
I should probably have a look at the IIB schematic - trace that out and go from there to check differences/similarities with the IIC RP10A when I get some time. I think they're completely different circuit designs though but could be wrong.

Perhaps the RP10A board features in some of the late IIBs? The LDRs were designed to stop popping when switching between channels. Either way once the + mod is done to them on all the boards, they end up the same circuit wise. It's just a lot harder to do on the RP10 and SP10 I would think.

For differences between the two... two identical IIC+s with the same board and the same month of production will sound completely different so good luck!

Re: Mark IIC+ Schematic (correct!)

Posted: Wed Feb 13, 2019 10:54 am
by discostu29
I have recently bought a IIC++ modded in 2016 by Mike B just wondering if you would be interested in photos etc to figure out the mods done from + to ++?

Mike B may retire anytime now and will take the mod with him, i think there will be interest in this mod.