IIc+ (RP10/SP10) vs. IIb (RP9C/SP9C)

[erickompositör72]

I'm curious to get more information on these two preamp circuits: how they are similar, and where they differ. I'm moving this from another thread I started:

I re-aquired the Mark IIb DRGX that I sold last summer. It has the RP9C preamp board.

n.b. - I stopped playing guitar for 17-ish years, and started back up again around last March (2020), so my assessments made last summer were made when I was very rusty and did not have great guitars to play through the amp.

Here's what I found, now having the IIb DRGX back in my possession-

The stock Mark IIb with the RP9C and export transformer sounds WAAYYY closer to my IIC+ DRX than I was expecting:

1. The saturation/gain is very, very similar. The liquid quality to the leads is very, very similar. I don't need any type of pedal/boost to get that liquidy note connection

2. The bass is not quite as tight, but it can still do metal rhythm with a scooped V EQ (I don't play metal anymore, but sometimes chug a few riffs for fun)

3. The voicing is MUCH closer to the C+ than a IIb S with the SP9A that I had (which I also had loop-mod'd). The RP9C still has a tiny bit of this nasal-mid frequency compression that comes through on certain notes, with certain pickup configurations. This frequency compression was not there in either IIC+'s I owned (one RP10, one RP11). The RP9C, though, was much nicer sounding (to me) in this regard than the IIb with the SP9A. The SP9A had heaps of that *****-mids compression, and I had to struggle to both dial it out, and alter my playing technique to attempt to mask it.

n.b. - After reading more from others, it seems that many do like the 9A voicing for its clean sounds, and its sound when pushing the clean channel into breakup. That's not what I use the amp for, so this doesn't really do anything for me

4. The stock IIb DRGX RP9C does not have quite as pleasing a vocal, crying note bloom as the IIC+'s (but still quite nice, and this is very guitar-dependent). For me, my IIC+ DR with the RP10 had the most incredible bloom and vocal/crying quality. The IIC+ DRX with the RP11 (that I still have) also has an incredible vocal/crying quality to single lead notes. After I had my IIb S with the SP9A board loop-mod'd, it then actually had that IIc+ vocal/crying quality, presumably as part of what Mike B did along with the loop-mod.


I am hoping that (assuming he does mods again) I can get this IIb DRGX loop-mod'd, and it will then acquire that vocal/crying quality for sustained single notes. If I can get that, I'd say I'm 95% there as far as the things I love about the C+

I wonder if he can do some voicing of it to remove that mid frequency compression thing? If that's possible, this amp's lead tone would be indistinguishable from my IIC+'s. Fingers crossed!!!

 

[GJgo]

IME the nasally quality is just an amp to amp thing. Most have it, some don't. I've had 2 or 3 that don't and they are amazing. You have to play with the GEQ off to really tell for any given amp. The four best Marks I've had (a B+ and three C+ (out of the 6 I've had)) could play no EQ and it was never missed.

The loop modded RP9C IIB IME has fantastic grind and bloom, but it still doesn't have the C+ liquid lead. It's great, jut not C+ great. Still a better lead tone than any other Mark I've had. The III black w/ the 105 is in the same camp. Honestly the only other Mesa that's done that liquid lead thing for me was the Badlander.

It really should be no surprise to anyone that the RP9C IIB (the last amp before the C) and the black stripe III (The first amp after the C+) are the closest in feel & tone to a C+. That's how incremental changes over time work.

 

[erickompositör72]

IME the nasally quality is just an amp to amp thing. Most have it, some don't. I've had 2 or 3 that don't and they are amazing. You have to play with the GEQ off to really tell for any given amp. The four best Marks I've had (a B+ and three C+ (out of the 6 I've had)) could play no EQ and it was never missed.

The loop modded RP9C IIB IME has fantastic grind and bloom, but it still doesn't have the C+ liquid lead. It's great, jut not C+ great. Still a better lead tone than any other Mark I've had. The III black w/ the 105 is in the same camp. Honestly the only other Mesa that's done that liquid lead thing for me was the Badlander.

It really should be no surprise to anyone that the RP9C IIB (the last amp before the C) and the black stripe III (The first amp after the C+) are the closest in feel & tone to a C+. That's how incremental changes over time work.

It's fascinating. IME, the only consistency (and that's only based on 2 examples: a IIb DRGX and a IIC+ DRX) I've found is that the export simul's seem to have tons of gain.

I'm counting my lucky stars, because my IIb DRGX (with the RP-9C) actually has as much or more liquidy-ness than both of the IIC+'s (DR & DRX)

Like you, I'm leaning towards just holding on to the IIb.

FWIW, the IIb I had that was a honk-fest was slightly better after the loop mod. The Mark III Red Stripe DRG that I had had this annoying upper-mid compression. Not quite "honk," but something that just kept it from sounding as "smooth" as I wanted.

 

[GJgo]

I'd suggest focusing on an amp as the sum of the parts. For example, of all the C+ I've had the HRG with the X101 was my least favorite. It had the weakest gain. Don't get hung up on the soup, focus on the amp as a whole. Some are just better than others.

I've had 6 III as well, and except for the III black 105PT they were all varying degrees of upper end harsh. IMO the IIB > III.

 

[Joey1970]

From my experiences, I have liked the Mark IIB loop-mod amp better than any Mark III, except for one 75 watt red stripe, and it was a freak.

 

[woodbutcher65]

I just acquired a hardwood Mark IIB combo, a straight 60, serial number 10031. I haven't opened it up yet, but it works absolutely flawlessly and was clearly treated like a family heirloom at all times. I look forward to seeing what board is in it and given its age, if it's never been recapped, of course I'm going to do that. And install reverb if I can.

I need to spend more time with it before I can give a tone report.

 

[GJgo]

The 60s are super pissed off, possibly my favorite tone of all the power sections.

A loop modded RP9C is a fantastic thing, for rhythm there are things I like about it more than the IIC+.

 

[woodbutcher65]

Any chances you can reveal what was done in the loop mods?
This IIB could use some tweaking. More lead gain to get closer to the liquid smoothness of a C, and tighten up the slightly flabby bass, for starters.

 

[GJgo]

Here's what I did. a) but the chassis in a box. b) Send it to Mike B. c) Pay the man for his expert work.

Keep in mind that even with the RP9C, the non-Coliseum IIBs aren't quite as tight in the ***. The IIB Colis are the most beastly amps Mesa ever created, I believe due to having no negative feedback.

 

[user 41014]

Jeremy, remember the S loop mod you played? It's not the coli but it's pretty solid iirc. It's been a while since I cranked that one.

I thought someone here had the loop mod. I thought I had it in my notes somewhere and might. Mike is not too subtle about wanting out. Your steps b and c will no longer be an option shortly.

I think you sent me the parts list when you had the loop mod idr. I have the S loop mod and with 7 B's atm I'm sure I could play the which one doesn't look like the other game. Looking at the C+ might help too since that seems to have "cured" the loop. And the C may play a missing link role.

Working on the B coli has me wondering if much of the "loop mod" is really just pulling it from a different spot in the circuit. Looking at the SP9A I'm working on and the SP-8B handy the loop is pulled from V2B and returned there as well.

I'm no expert for sure but that looks to be right after the tone stack. Maybe some kind of buffering is being used or they found a cleaner place to insert the loop. That along with the normal evolving component tweaks is likely the majority of the mod. But I wish I knew for sure!

Looks like i may need to pull some more chassis.