Mark III C516 tweaking...

[effitall]

So I've been playing with my green stripe MkIII. I did the C27 and C30 mods...Already have the Reverb mod...But I was still not happy with the overall aggressiveness in the highs of the amp. The presence control was kinda unusable and spent all of it's time pretty much off. The amp seemed kinda dull/dead without any presence, but pretty much any presence hurt the ears.

Talking frequencies....The presence control seems to dip too far down into the spectrum. I want to bring up the "air" "sparkle" or "presence" of the amp...Not the "treble." So am I correct in tweaking C516 lower in value to shift the response of the presence control up in frequency?

 

[Boogiebabies]

What speaker and what power tubes ?

On any MK series I have every owned the presence has never been over 2 using V-30's or 12L's. On occasion with vintage greenbacks I would up it to 4. It's a very powerful tone control.

Not to nitpick, but did you use ceramic disc caps on C27 and C30 ?
The more I tweak, the more I find silver mica or even Wima poly caps to be
smoother.

Is C516 a .01uf Orange Drop ?

 

[effitall]

I used a SM on C27...I used a PS series Orange Drop for C30.

Speakers are Scumback H and M75's. Power tubes are Boogie STR440 and 447 6L6/EL34 respectively.

At first I was a little bothered by the aggression...The C30 mod was great, but I'm still missing the "air." The 2k and 6.6k sliders are a little too low for what I'm wanting. The "presence" control in my mind should "fix" this...But I hear it grabbing too far down (seemingly down to if not below 2khz).

C516 is a 0.005mf OD 715P.

 

[Boogiebabies]

Essentially the 5000pf and the 56K is the mixer for the presence. If you leave the 56K in, the best idea I can offer is to lift one leg of C516 and try adding a 1000pf in series until you get closer to your ideal sound. Or remove C516 and start out with a .01uf cap and work down.

The .005 is the value on the IIC+, but Mesa also stated that on the MK III is should be .01. Go figure.

 

[effitall]

Okay....So...With C516...I went from .005 to .001 and that was kinda alright...For giggles I popped in a 120pf. I don't think I even want to try anything else. Presence stays pretty much on 10 and just ROCKS!

Another thing...I got all new electrolytics from Boogie and installed them yesterday. I didn't do any specific before/after sound files...But the amp seems to have more "punch" on the grittier stuff. Before it seemed a little too spongy in Class A for "heavier" stuff and anything fast and articulate needed to be in Simul-Class. Now it seems that Class A is fairly "tight" and Simul-Class is just brutal.

I'm also considering the R2 volume mod and saw some talk about replacement LDRs but need to look into those a little more.

If there's any one real gripe I have about the amp is that I wish I could have a preset V1 level for R2/Lead and a different level for R1. I might ponder that a bit. I think that tweak would make more sense than the R2 mod...But I might be mistaken. Like I said...I need to read up on those a little more.

 

[Boogiebabies]

Pretty soon it will be a MK IV...... 24 LDR's, wine and cheese.

I don't exactly know what the mixer value of 56K/120pf is but if you like it, good for you.
It's most likely seriously shifted the presence down closer to an additional or second treble. Is it even audibly different from 1-10 ? Do dog's in the neighborhood go howling?

 

[effitall]

Ha ha! Well...The best I can say is that it just adds life to the amp. With the presence knob set low, the amp gets more rigid and stale....When you crank it up...There's more life. I should stick a scope on it and see if there's any nasties....But the amp appears to be stable and sounds badass. Higher levels of presence increase the volume of the amp...And I tried to "level-match" full presence verse no presence and increased master volume...There's no comparison...Full-tilt on the presence just smokes.

 

[Boogiebabies]

Well, as long as you like it that is all that counts. How it would sit in a band mix is a different story. If you could make the 120pf/5000pf switchable you would be covered in case it can't cut.