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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 HOPEFULLY drawn up an accurate IIC+ schematic of the main sections. I say hopefully because I do not own a IIC+ and cannot verify this info. This is taken from info I can find on here from chipaudette who had a 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!

It's also taken from my experience of verifying my Early III Black Stripe, the mainly accurate schematic from the sloclones forum and chipaudette who drew up a IIC schematic here and took some gut shots: https://get.google.com/albumarchive/109 ... source=pwa

Please let me know if there are any errors. But please only from someone who has a genuine IIC+ to verify with!

Anyway the schematic is here. Hope it's of use to someone! Main things to note that differ compare to the official schematic are the various values used for certain components, and the power section.

EDIT Updated to 100% correct from tracing a IIC I bought and from pictures from a IIC that had been upgraded to a +

IIC schematic: https://drive.google.com/open?id=1mpJFs ... 81rlggkt6M
IIC+ schematic: https://drive.google.com/open?id=1ieTnM ... RIDwbLAcUQ

Enjoy!

Jon

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. Info I got was from here: http://forum.grailtone.com/viewtopic.ph ... 49&start=0

I don't think it has anything to do with the ++ mod but certainly wouldn't harm anything and would definitely add some gain when combined with a 10pF on V2! Try it and see :)

Re: Mark IIC+ Schematic (correct!)

Posted: Thu Apr 12, 2018 7:34 am
by jrb32
Link updated to include correct EQ and Power Section, along with a few corrections from info out there. This includes, hopefully, the mystery EQ cap.

It also gives 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.

I have no concrete info on the Reverb or the High Voltage Supply for a IIC+ so cannot compare these at the moment. Apart from that is pretty much as accurate as you'll get until someone traces theirs or offers me one to trace 8)

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

Thanks,

Jon

Re: Mark IIC+ Schematic (correct!)

Posted: Wed Dec 12, 2018 12:09 pm
by jrb32
Link updated to include 100% correct info. As in I bought a IIC, traced that, then compared it to a C+ from pictures from an upgraded C+ that was originally the same as mine. Then added info I can find on here and other pictures I've seen of factory IIC+s.

IIC schematic: https://drive.google.com/open?id=1mpJFs ... 81rlggkt6M
IIC+ schematic: https://drive.google.com/open?id=1ieTnM ... RIDwbLAcUQ (same as link above - updated that as well)

Enjoy!

Jon

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 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 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 board so that C9 comes first off V2B. Apart from that, identical circuit wise. Layout slightly different.

The RP11A board was 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 probably designed in mind to make it an easier upgrade to a C+ or could be based on the SP11A? I would imagine these stock are different circuit wise to a stock IIC RP10A. I have one picture of a non EQ non Reverb IIC with an RP11A so not much to go on really. Same with a IIC SP11A I don't have much info.

The SP11A board was used in production on all the non Reverb IICs and the IIC+s without any revision change as far as I am aware.

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 apart from C9 and R105 swapped over which shouldn't make any difference? I'm not an amp designer though so I'll leave that to someone who knows what they're talking about!

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.