Mesa Mkll b combo - Loop mod? Or?…

[ConcreteVampire]

Hello gentlemen,

Looking into having this done. I understand it’s basically updating the loop and installing another master in the slave pot space.

I understand it tightens it up, and adds significant gain. (Not Mk 2c+ Levels, but I’m not looking for that much. More call six rock/hard rock than metal)

I have also heard care needs to be taken with values as is it may have a negative effect on the clean channel, which is really awesome. (Less warm, etc…)

Thoughts?
Experiences?
Schematics?
Or suggested mod choices or values?

I can also escalate the mod to + plus levels, I do know it’s a different board which will keep it from being “Correct”.

It’s just a combo unit in a Mklll combo box. So I’m not ruining a 5k amp, ; )

But it is a pristine refurbished 83 head unit.

Likely going to pull the Shadow for a Creamback.

Thanks for any input!

 

[GJgo]

Do you need shimmering cleans?

Do you need the loop to actually be good?

Are you doing it yourself or sending it in?

 

[ConcreteVampire]

Do you need shimmering cleans?

I want the clean cc the same as they are now
Do you need the loop to actually be good?

I want to loop to be as good as it is now. I understand is a rudimentary loop as it stands. I will be using some kind of switching to have the loop be a pedal base channel access.

Are you doing it yourself or sending it in?

I’m having it sent into one of the best amp builders in the business.
Thank you

 

[JimAnsell]

this may be of interest


totally get the mod. it adds another gain stage, and makes the lead channel sound amazing.

 

[GJgo]

I want the clean cc the same as they are now
Do you need the loop to actually be good?

I want to loop to be as good as it is now. I understand is a rudimentary loop as it stands. I will be using some kind of switching to have the loop be a pedal base channel access.


I’m having it sent into one of the best amp builders in the business.
Thank you

Then I'd recommend not loop modding it. Just have it serviced.

I have a IIB+ & Mike B. modded it for me so I know the before & after. It did get dirtier, and in my case the gain is now between my C+ & C++.

 

[IIBornotIIB]

Then I'd recommend not loop modding it. Just have it serviced.

I have a IIB+ & Mike B. modded it for me so I know the before & after. It did get dirtier, and in my case the gain is now between my C+ & C++.

Same experience with loop modding two IIB HRG’s… detracted from “clean” cleans, and added more gain.

 

[Racerxrated]

Yep I’d even go so far as to say, the loop modded B Coli I had was gainier than any C+ or the one ++ I owned. TONS of gain.

 

[danielraible]

I own a loop-modded Mark IIB, and do really enjoy the clean tones. Certainly different than fender, and even Mesa Heartbreaker or Mark IV cleans, but very usable at gig volume for a great warm jazz sound.

BUT, I treat the IIB like a single channel amp. Run the dials and set up a great clean sound, jam. I like to think Jerry Garcia would dig the tone. Now rerun the dials and set up a great vintage saturated fusion lead sound kinda like Santana, jam again. Tweak a little further from there to get into high gain rhythm territory maybe with a boost to tighten up the lows...chug away...

If you want the amp to deliver a bunch of clean headroom while instantly being able to switch to an optimized lead channel, than the loop mod might not be for you. The shared controls and enormous range of gain on tap is a challenge. At least I've never been able to find that balance given guitar, pickup, speaker swaps, etc. For me the IIB(+?) works best with an amp switcher and dedicated to a single sound.

Mine doesn't exactly resemble the schematics, nor the Guitarologist's video (which is great BTW), so someday when I have some spare time I'd like to document the circuits in mine and post a video of the full schematic, both to keep this one going but also for other owners (and techs) who are going to need servicing over the next few decades. Of all the Mesas I've owned, I have yet to see one really match the schematic.

 

[ConcreteVampire]

this may be of interest


totally get the mod. it adds another gain stage, and makes the lead channel sound amazing.

This video was the inspiration for the thought thanks!

 

[ConcreteVampire]

Then I'd recommend not loop modding it. Just have it serviced.

I have a IIB+ & Mike B. modded it for me so I know the before & after. It did get dirtier, and in my case the gain is now between my C+ & C++.

I am leaning towards the mod, 90% of my live work will be with the dirty channel. I am looking into a switcher for the FX return to get pristine cleans.

 

[ConcreteVampire]

I own a loop-modded Mark IIB, and do really enjoy the clean tones. Certainly different than fender, and even Mesa Heartbreaker or Mark IV cleans, but very usable at gig volume for a great warm jazz sound.

BUT, I treat the IIB like a single channel amp. Run the dials and set up a great clean sound, jam. I like to think Jerry Garcia would dig the tone. Now rerun the dials and set up a great vintage saturated fusion lead sound kinda like Santana, jam again. Tweak a little further from there to get into high gain rhythm territory maybe with a boost to tighten up the lows...chug away...

If you want the amp to deliver a bunch of clean headroom while instantly being able to switch to an optimized lead channel, than the loop mod might not be for you. The shared controls and enormous range of gain on tap is a challenge. At least I've never been able to find that balance given guitar, pickup, speaker swaps, etc. For me the IIB(+?) works best with an amp switcher and dedicated to a single sound.

Mine doesn't exactly resemble the schematics, nor the Guitarologist's video (which is great BTW), so someday when I have some spare time I'd like to document the circuits in mine and post a video of the full schematic, both to keep this one going but also for other owners (and techs) who are going to need servicing over the next few decades. Of all the Mesas I've owned, I have yet to see one really match the schematic.

Thanks for the input!

Is there any schematic for this out there? I trust the guy I’m sending it to will execute an excellent loop, and well voiced additional master.
Any additional intel I can provide would be nice

 

[ConcreteVampire]

Then I'd recommend not loop modding it. Just have it serviced.

I have a IIB+ & Mike B. modded it for me so I know the before & after. It did get dirtier, and in my case the gain is now between my C+ & C++.

I purchased it with the full service, new caps tubes etc.

 

[WarHed]

The problem with IIb's is the circuit was changing every few months. There's no consistency between amps or circuit diagrams for this reason.
I have a loop modded, or whatever, IIB and it has about as much gain as my more modern marks, but it pretty wooly and vintage sounding. It's not very good for metal tone imo, at least compared to later revs anyway

 

[IIBornotIIB]

The problem with IIb's is the circuit was changing every few months. There's no consistency between amps or circuit diagrams for this reason.
I have a loop modded, or whatever, IIB and it has about as much gain as my more modern marks, but it pretty wooly and vintage sounding. It's not very good for metal tone imo, at least compared to later revs anyway

There were 3 preamp versions in the IIB lineage between 1980-1982/3. .They got increasingly gainier and somewhat tighter through the evolution. The culmination was in the C+ where they got it “just right” between clarity, harmonics, feel and a functional loop. I will say that my first series (RP9A circuit) IIB w/ loop mod is an exceptional version- it slays. May be amp-to-amp variation (sum of the parts), if yours feels ”wooly”,… mine is tight as a gnat’s @ss.

 

[JimAnsell]

There were 3 preamp versions in the IIB lineage between 1980-1982/3. .They got increasingly gainier and somewhat tighter through the evolution. The culmination was in the C+ where they got it “just right” between clarity, harmonics, feel and a functional loop. I will say that my first series (RP9A circuit) IIB w/ loop mod is an exceptional version- it slays. May be amp-to-amp variation (sum of the parts), if yours feels ”wooly”,… mine is tight as a gnat’s @ss.

i didn't know this before. got me looking back at some old pics. check out this spotlessly clean IIb chassis i had like 15 years ago. it looks way different than the one in the video. that "trace to nowhere" in the video, looks populated with a .47 sprague orange drop in this pic.

 

[danielraible]

And it appears you have an RP-9 preamp board, maybe an RP-9A if you move the green wires over. 7C power board.

I need to pop mine out and check.

 

[ConcreteVampire]

The problem with IIb's is the circuit was changing every few months. There's no consistency between amps or circuit diagrams for this reason.
I have a loop modded, or whatever, IIB and it has about as much gain as my more modern marks, but it pretty wooly and vintage sounding. It's not very good for metal tone imo, at least compared to later revs anyway

That’s the bottom. Obviously, I’ll pull it and take a snap tonight…

 

[IIBornotIIB]

That’s the bottom. Obviously, I’ll pull it and take a snap tonight…

Most likely RP9A, based on ‘81 production.

 

[ConcreteVampire]

finally some pics sorry bout the delay. What could the SG written on both chassis ends mean?

Please clue me in on the insert points of both the inputs on the bottom of the chassis.

Tnx!

 

[IIBornotIIB]

S= Sixty W G= GEQ. If it had reverb, it would be designated SRG.

The jacks on the chassis: One is for pre-amp out / power amp in to run with another Boogie, the other jack should be a stereo jack which you can plug one of Mesa’s two-switch foot switches which would enable foot switching of GEQ and Gain Boost. (On amps with reverb it normally controls reverb and GEQ).