Factory Mark IIC++ Models

[DaveP]

Can someone tell me about the Mark IIC++ Factory models. I recently heard of some of these units that left the Mesa
as factory C+'s but they were C++ meaning when the middle control pushed in it the normal C+ but it also pulled to give a slight
variation. Has anyone seen one of these or played one? any info would be greatly appreciated.

 

[DaveP]

LOL, yes I did. I just spoke with Mike B today and my initial work order i told him to make it factory original. He assumed I noticed
this difference and stated it is factory original. He told me a handful of these where produced
I said then leave it be. He will be replacing some caps and other general maintenance.
I didn't even notice the mid pot was a pull pot. Doh!!

 

[chipaudette]

Dang!

I thought that I was the only one who thought to put a pull pot for the mid on my IIC(+). Dang! I guess there's nothing new under the sun.

I've got my mid pull pot bringing in a 2.2u cathode cap on V2A (well, what would be V2A for most people). It sure does add a lot of saturation, but I actually find that I don't use if very much at all. I don't really like the quality of the saturation.

Maybe it's that I'm using an electrolytic cap. It doesn't really appear that there are any other electrolytic cathode bypass caps in my IIC(+). Maybe there's a reason for that. Maybe I should try another type. Or another value.

What does the pull pot do in your amp? Anyone else got a pull pot in place of their mid pot on their IIC/IIC+?

Chip

 

[DaveP]

From what I found this is referred to aa a Metalica mod or Petrucci mod. Some Mark IIC+'s left the factory this way others
were modded to the same specifications. According to Mike my amp left the factory as a C++.
Basically from the information I found you can have a normal C+ mode and the C++ which adds a ton of extra gain on tap.
I will see in couple of weeks when I get it back.

 

[chipaudette]

Yeah, I'm familiar with a lot of the conjecture over the "C++", the "Hetfield (Metallica) Mod", and the "Pretrucci Mod". I'm also familiar with the numerous ways that gain in a C+ can be increased (boogiebabies has had lots of good comments in this area on other threads). The addition of the cathode bypass cap on V2A is one such example.

What was surprising to me is that I didn't know that anyone (like Mesa itself) had these mods switchable via a pull pot on the mid control. That is something that I hadn't heard before. I thought (stupidly) that I might have done something that was a smidgen unique.

For example, in other threads on the C++ or Hetfield mods, people talked about how the mod destroys the sound of the clean channel. They talked about how you could never really get a good clean sound anymore. Clearly, they didn't make it switchable. If they had made it switchable, it wouldn't have destroyed the clean channel. My switchable cathode bypass cap, for example, leaves the amp to be stock when the pot is pushed in (well, it does have a little bit of extra wire, but that's it). I was always surprised that no one ever talked about making it switchable. Seemed obvious to me. Sounds like it was obvious to Mesa as well.

I'm still very curious to get confirmation on what exactly was being switched on the factory-made C++. Was it a cathode bypass cap on V2A? Or was it some other component (or combination of components) being switched in/out?

Cool.

Chip

 

[DaveP]

I will try and get clarification on this Chip. Now that I did a little homework on this I have the right questions to ask now.

 

[chipaudette]

If it is the cathode bypass cap, I'm also curious what value they chose...

1) They could have gone with something big...like 10-20 uF, which would have given a full-frequency boost. This might make things a little tubby, but the lead sound might be really liquid.

2) They could have gone with something medium...like 2.2uF, which they used on the Mark IV as the "harmonics"/"Mid Gain" switch when in the "Mid Gain" position. I use 2.2uF. It's decent...but mine is kinda fizzy sounding.

3) They could have gone with something small...like 0.68 uF, which might just compress the highest highs.

I'm curious to hear what is in a factory-made C++. So so so curious.

Chip

 

[DaveP]

I just verified some information,
They use a .47uf cathode bypass cap. This is engaged when the middle pot is pulled. It is then routed through a network of resisters to keep the upper mids intact. It does loose a little bottom when this is engaged but that can be added with the EQ. There is also a 1/4 jack located on the bottom of the amp that toggles this function as well.
Only about 12 of these were produced from the factory. (give or take a few)

Interesting info.

 

[chipaudette]

So if it is foot-switchable as well as switchable from the mid pull-pot, it must be actuating an LDR or relay (like with channel switching via its footswitch or pull-pot). If some LDR/Relays are involved, lots of changes could be happening in the amp. That makes it harder to guess about what is going on.

Your added info about the 0.47u cap and the resistor network is very intriguing...but, unfortunately, it doesn't make 100% sense to me. The 0.47u cap is fine...though that's pretty small. Do you know if the cap is on V2A or somewhere else?

Also, what is more confusing to me is your comment about the resistor network. A resistor network makes no sense on the cathode of V2A or of any other cathode, so it must be brought into the circuit somewhere else. The info about the availability of a foot-switch (ie, it being evidence that there are relays/LDRs involved) allows this resistor network to be located practically anywhere. Was there any mention of where it was?

My wild guess is that it is a resistor in parallel to the 680K resistor (to ground) just prior to grid input of V2A. If the 0.47u cap is really on V2A, it's input headroom to mid and upper mids and high frequencies is now really reduced (ie, its output gain is tremendously increased). If you keep the circuit as-is, the full signal strength will really make V2A over-saturate and it'll sound not quite like how most people would prefer. Putting a resistor-to-ground in parallel with the 680K will cut down the signal a little before it reaches V2A. That'll keep the tube from over-saturating (ie, turning to complete mush).

Because of the in-line caps in the main signal path, one could describe the resulting change as reducing some bass while keeping the upper mids intact while keeping V2A from getting too saturated. That kinda sounds like what you described. The trouble with my theory is that it only adds one resistor and not a "resistor network". So, my conjecture could be completely wrong.

All the info you've gotten so far is so juicy. This is so fun. I really appreciate what you've shared. Of course, I'd love even more info or, dare I dream, a schematic of the mods. Man, that'd be sweet.

Thanks for the fun!

Chip

 

[JOEY B.]

Very interesting info about the 12 or so "factory modded" amps. I'll keep my C+ amps stock and goose them with the RC Booster when I feel the need. 8)