Older MKIV = MKIIC+ ?

[jm1681]

The MKIV I'm referring to in this thread http://forum.grailtone.com/viewtopic.php?t=9544 is a bit old and it got me thinking...

Wasn't the lead circuit in older MKIVs identical, or close to the MKIIC+? Not sure what distinguishing features I could relay, but the one thing that sticks out in my mind is that it had a "Boogie" name plate, not a "Mesa/Boogie" name plate.

 

[Boogiebabies]

The IVA circuit is based on a 60/100 schematic of the IIC+. It is not based on the Simul which has no bright reduction cap. On the IV A this is the V3B - C23/R276. the original IIC+ 60/100 used a .001 cap instead of a 500pf, but they both cut highs. The other cap change is the C2/R102. The original IIC+ used a 10pf for a brighter clean channel and it has an effect on the lead channel as well. Mesa used a 20pf here. Both these changes are consistent with the mods done to IIC+'s to remove gain and brightness. The MK IVB has the 20pf, but not the 500pf on R276. It also has a minor change to the bypass cap on R332 in the lead circuit. It was brightened with the use of a 750pf cap instead of the IIC+ and IVA .001, or 1000pf.

I prefer the MK IVB and stock IIC+ Simul-Class amps. For me, the .001 or 500pf bypass cap just dulls the shred they have stock.

Good Luck.

 

[jm1681]

So it is based on a modified version of the IIC+?

Sorry, while your response is very precise, it is a bit confusing

 

[Boogiebabies]

Yes, you got it, don't feel confused. You did great deciphering all that babble.

 

[Boogiebabies]

That's a good question. The only schematic floating around on the MK III is that on from 1985. It would be interesting to try and follow the strip evolution, but whio has the time. I personally would be interested in the Green Stripe as I have one too and it rips major ***. Just from my use of it, I would say it is more like a MK IV B with a smoother lead tone. When compared to a stock Simul-EQ-Reverb IIC+, the + is smooth, but has an bit more natural brightness and shred to it. It also has almost unlimited headroom. Out of all the Stripes, I think the Green has the most headroom in comparison to the C+, but then again the outer sockets are wired in pentode so it seems to be able to emulate the C+, but not exactly.

I will see if I can dig up a III Greenstripe schematic.

 

[Boogiebabies]

Mine is in the 26300 range from 1990, Ian at The Boogie Files has a few 1998 models and they are in the 28,000 range. I don't think they made too many after the MK IV came out. IMO, it's a rather rare find.

 

[danyeo1]

I can tell you that i owned a IIC+ 60 watt non-simul head and i now have a IVA. The IV has more gain than my IIC+. But i still kinda liked the IIC+ because it was soo easy for me to just plug in and get THAT sound. With the IV I'm always messing with the knobs.

On the IV the middle slider seems to scoop the mids quicker than the IIC+. If i dip the slider it turns into scoop metal real quick.

But consider the cost, i wouldn't buy a IIC+ for the mega bucks they sell for since the IV is close enough for me. I sold my IIC+ for $3000 and bought the IV for $1100.

 

[Dersu Uzala]

...but then again the outer sockets are wired in pentode...

Peace of cake to rewire to triode mode, assuming EL34 are plugged in.

--Yours friendly (former) audio tube amp designer--

 

[Boogiebabies]

I can tell you that i owned a IIC+ 60 watt non-simul head and i now have a IVA. The IV has more gain than my IIC+. But i still kinda liked the IIC+ because it was soo easy for me to just plug in and get THAT sound. With the IV I'm always messing with the knobs.

On the IV the middle slider seems to scoop the mids quicker than the IIC+. If i dip the slider it turns into scoop metal real quick.

But consider the cost, i wouldn't buy a IIC+ for the mega bucks they sell for since the IV is close enough for me. I sold my IIC+ for $3000 and bought the IV for $1100.

You know, that is a very interesting point. If you look at the Mesa Graphic EQ as it progressed from the IIC+ to the MK IV you will see that the EQ circuit was run at lower voltages. In essence, I believe that the lowered voltage adds to a more natural interaction with the output circuit, kind of more of the amps natural tone and a less over powering effect of the graphic. All of the components and inductor values are the same, but they do behave differently. Not to get too techy, but I believe this is a by-product of Mesa incorporating the EQ amplifier on the main circuit board of the III and IV and they did not need higher( Negative) voltages to power it. The IIC+ has the EQ amplifier and the EQ controls on opposite sides of the amp and they are run through a mile of wire over the top of the preamp. The MK III and IV only have a few inches of wire and they are on the board. Small things can sometimes make a big difference.
But then maybe it was lowered for a purpose that made a better sounding EQ. Who knows !!!

 

[Antoine]

Boogibabies, your knowledge seems endless, thanks again for all these technicals description of our so lovely amps :wink:

 

[Boogiebabies]

Just a thought...