IIC or not to see? - loop mod

[electric mayhem]

Maybe some of the senior people on here, not a crack at your age mind you, can help me with something I was wondering.

We all know Mike has a loop mod which he obviously masters across several variants of pre-amp boards for the Mark IIB.

Since "everyone" wants a IIC+ these days, questions usually encircle how do I make my Mesa Boogie __fill_in_the_blank__ sound like a plus? Which OT I think is pointless for anything that is not a IIC+.

Maybe it's out there but I can't recall anyone talking about a loop mod Mark IIC. So would a "loop mod" IIC be a IIC+ or would it be an animal all on its own?

And does anyone have the mod to turn a peavey bandit into a IIC+? What about the Nomad IIC+ mod?
just kidding

 

[rarebitusa]

Maybe some of the senior people on here, not a crack at your age mind you, can help me with something I was wondering.

We all know Mike has a loop mod which he obviously masters across several variants of pre-amp boards for the Mark IIB.

Since "everyone" wants a IIC+ these days, questions usually encircle how do I make my Mesa Boogie __fill_in_the_blank__ sound like a plus? Which OT I think is pointless for anything that is not a IIC+.

Maybe it's out there but I can't recall anyone talking about a loop mod Mark IIC. So would a "loop mod" IIC be a IIC+ or would it be an animal all on its own?

And does anyone have the mod to turn a peavey bandit into a IIC+? What about the Nomad IIC+ mod?
just kidding

So I had my IIC upgraded to a +, not only did that change the lead chan gain structure (for the better) but it also, and almost as important IMHO, made the fx loop usable. As I understand it the rearrangement of the design relocated the fx loop after the lead stage where before on the IIC had been before it. They kinda both went hand in hand with the + upgrade. Not sure if that makes sense.

 

[electric mayhem]

So I had my IIC upgraded to a +, not only did that change the lead chan gain structure (for the better) but it also, and almost as important IMHO, made the fx loop usable. As I understand it the rearrangement of the design relocated the fx loop after the lead stage where before on the IIC had been before it. They kinda both went hand in hand with the + upgrade. Not sure if that makes sense.

Clear as mud lol.

I've got a IIB loop mod but I bought it that way so I have no before/after experience but a nick name of the loop mod is B+ which makes me wonder if it is specifically the settled on loop that really defines the IIC+.

The power sections are different from what I understand so a IIB is not a IIC+ or vice versa for good or worse depending on how one views that.

All the reports of IIB loop mod before/after indicate the gain structure or attitude is different and the reason why if you have a great IIB for what you do don't loop mod it because it won't be the same amp.

That suggests inherent gain structure change with the positional change in the circuit and I'm not smart enough yet to know if that involves a new stage on an unused triode, conversion of a cathode follower to a gain stage, exiting/re-entry where changed impedance puts the gain in a new ballpark, etc.

Yet it's called a loop mod, not a gain mod so I assume, maybe wrongly, that the prior gain stages are being left alone.

With a IIC+ conversion are prior gain stages changing? Tone stack changes? Plate resistors on the loop triodes changing that wouldn't change with just a loop mod?

Or is the final loop to rule them all essentially the IIC+ over the IIC with different layouts for the different boards?

I guess the same rule applies- if your IIC sounds great resist the urge to mod or convert it because it is going to change. But could I loop mod a IIC and not convert it?

Edit: If the loop test confirms a IIC+ maybe the answer is as simple as that?

 

[electric mayhem]

Maybe based on what you are saying the gain structure changes for the lead channel only though.

 

[rarebitusa]

Well I haven't looked deep into the IIB loop mod so I am at a disadvantage as to the details. However below is the tube functionality WRT to the +. The IIC and IIC+ schems were drawn up and provided by one of the forum folks here. I think it is ok to post them, if not I'll remove them. More mud for you.

MKIIC+​	OLD MKIIC​
V1a = Input Amplifier​	V1a = Input Amplifier​
V1b = Post Tone Control Amp​	V1b = Tone Control Amp​
​	​
V2a = Mixer Amp​	V2a = Effects Send Cathode Follower use 12AT7 for cleaner tone​
V2b = Effects Return Amplifier​	V2b = Output Amplifier​
​	​
V3a = Reverb Return amp​	V3a = reverb return amp​
V3b = PreGain Amp Lead Drive​	V3b = ½ Lead Drive Amp (MKIV 1st lead gain stage (3rd lead stage = 1st lead GAIN stage))​
​	​
V4a = PostGain Amp Lead Drive​	V4a = ½ Lead Drive Amp cascoded (MkIV 2nd lead gain stage (4th lead stage = 2nd lead GAIN stage) )​
V4b = Reverb driver (send)​	V4b = reverb driver (send)​
​	​
V5a = phase inverter / output driver 1​	V5 = phase inverter / output driver​
V5b = phase inverter / output driver 2​	​

 

[FedWar]

You should search this forum, there should be circuit changes in both schematics and layout formats that show you the required changes based on the pcb revision board.
A IIC pcb reworked becomes de facto a iic+: loop improved, pre and power amp are set to iic+ specs.

Then there is the iib loop mod.
Which basically fixes the iiB loop, adds a post fx loop volume knob in the back and adds more gain and to the preamp section since the stages are set like they were supposed to.
I have a RP9A loopmodded by MB in the 90s.
Does is sound like my other iic+ I have? yes and no.
It is more bassy and it sounds more vintage.
It can with the correct geq settings but I don't want it to.
I prefer to run it with treble shift OFF and geq OFF.
It seems to have been calibrated to run great without geq.
So I like to use it for angry vintage hot rodded tone or for edge of breakup as well.
I love the way it is and I will never sell it for sure.
I do recommend to do the loop mod if you can but the fi al result will vary based on the pcb revision (rp 9a rp 9b or rp 9c which is the closest to a iic)

 

[electric mayhem]

Thank you to rarebitusa and FedWar!

That chart you posted shows some changes throughout the early stages and a maybe the changing of a cathode follower to a gain stage on V2.

So to sum up one wouldn't be able to do a loop mod on a IIC without it becoming a a IIC+.

My bare bones S IIC with SP 10 to me is a gem and I wouldn't change a thing on it. I'm hoping to get another non-converted IIC with 4 power tubes to see if I like it as much.

 

[electric mayhem]

The IIB is my weakness. I'm confident I'll have every pcb revision despite my current over-weighting of the SP 9A. I do have the SP 8B and RP 8C but never played a 9C. My preference is a coli of every version.

My 1st SP 9A is a 60W loop modded and is amazing. I don't feel the handful of non-loop modded are deficient.

I'll be adding to my IIB's in the coming year and maybe selling a pair of SP 9A coli's since I have 3. I already fully serviced one but am wanting Mike to loop mod a 2nd IIB for me before he retires his solder station in favor of a fishing pole.

 

[rarebitusa]

Thank you to rarebitusa and FedWar!

That chart you posted shows some changes throughout the early stages and a maybe the changing of a cathode follower to a gain stage on V2.

So to sum up one wouldn't be able to do a loop mod on a IIC without it becoming a a IIC+.

My bare bones S IIC with SP 10 to me is a gem and I wouldn't change a thing on it. I'm hoping to get another non-converted IIC with 4 power tubes to see if I like it as much.

It may be worth a call to MikeB to see if he could do a IIC loop mod.

FWIW my IIC, which I bought new in 83, stayed a IIC until 2017. The main driving force to upgrade was actually to fix the loop to facilitate 4CM. The + significantly changed the lead chan voicing no doubt. I'm used to it now, but it's a much different animal.

 

[electric mayhem]

It may be worth a call to MikeB to see if he could do a IIC loop mod.

FWIW my IIC, which I bought new in 83, stayed a IIC until 2017. The main driving force to upgrade was actually to fix the loop to facilitate 4CM. The + significantly changed the lead chan voicing no doubt. I'm used to it now, but it's a much different animal.

I was going to see about him doing some work so I'll ask if a loop mod IIC is a thing.