Mesa Boogie SOB Limiter Mod?

[edge59]

Not having a SOB at this time, I only played one back in the mid 90's a few years after a real mid 70'd Mark I that had Pull boost and pull brite, what an amp! My Mark III sucked mud next to that amp. Later when I played the SOB, I was amazed of the sound! I am leaning to think modding a SOB to Mark I specs may give the amp more bass response and or more gain in the bass department, making high gain settings somewhat muddy, but will sound like a Mark I. I did own a Mark I Reissue in the late 90's with Koa cab etc, heavy beast, did not sound as good as the 70's Mark I or the SOB. It has some things different about it, it had metal film resistors for one, the circuit was somewhat revised and like whats in the Mark V to a degree, I modded it with some of Gil Ayans mods, some I liked some were so-so for that amp, I did add a Gain boost and pull bright like the mid 70's model had and a treble shift to thicken up the upper mids, plus a bias pot and ended up selling it The buyer was estatic with the tones, and primarily used it in his studio. Now the Lonestar is very similar for a 2 channel amp, looking at the schematics show the second or Lead channel to be very much the same as the old Mark I preamp -wise. But... with all the switching components and different transformers, tubes and all, they sound a bit different. A bias pot will help these amps dial in a sweeter tone, but someone will need to remove the smog control devices in those amps to let the tone open up more.....

[methodofcontrol]

well... for now, my ambition has waned a bit. aside from the reverb circuit and extra tube, i would need another transformer and tank and about 10 free hours on the bench when i don't need my amp.i have an old boss RV-2 i've been using for reverb and my bench is full of friend's amps needing repair.
when i opened the SOB up a few days back, i forgot how little there is inside there. it looks like a fender except it breaks up like a rock amp when pushed. i also never realized there was a choke in that amp, it hides quite well behind the PT.
so...for now, this project is back burner stuff for for me.

again i ask, no one knows what H.O.B. stands for? i've seen SOB's referred to as HOB's, and HOB is even written on the side of my chassis.

[J M Fahey]

Don't really know, but the chassis being the same in both versions, SOB is the combo (no doubt about that) and (H)OB *might* be the standalone (H)ead version, electrically the same.

[methodofcontrol]

edge59, thanks for the GIF! didn't study it until just now. i don't understand the 102 cap near the master volume, what's that about? oh wait.... i see, it's a 102 cap in series before a 1m pot for presence control? wouldn't the presence control be attached to an OT tap, that doesn't seem to be drawn in? my amp already has presence control wired to 8 ohm tap, if i moved it to the 4 ohm tap, would that make the whole amp bassier? or just the presence control?

oh... and just called MESA/BOOGIE about some of this stuff. for those who are curious the "H" in HOB just stands for "Hundred". as in, "this SOB will be a 100w'er".

[edge59]

Yes the presence in that Schematic is based on the reissue Presence. If you have the stock presence, it should give you more bite and sizzle. The PPIMV has been done by someone here I think, and it may a bit overkill for some, but effective.