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Studio Premp w/ MKIIc+ mod
http://forum.grailtone.com/viewtopic.php?f=5&t=56806
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Author:  coupie666 [ Sat Dec 24, 2011 3:54 am ]
Post subject:  Re: Studio Premp w/ MKIIc+ mod

Hey sorry to interrupt, but I am very iterested in doing the IIc mod to my
Studio preamp!

MBoogman, Any pictures you could share with me would be greatly appreciated! Thanks in advance and have a Merry Christmas!

Author:  Shane C [ Fri Dec 30, 2011 6:35 am ]
Post subject:  Re: Studio Premp w/ MKIIc+ mod

Howdy guys,

I hope you all had a great Xmas and all that jazz. Ive been doing a little research and I'd like to share.

I think the 170k resistor shown on the C+ modded Studio schematic is incorrect, the original MKIIC+ schematic is nearly unreadable and another version shows the resistor as being 1k. Also 170k is a non standard value which means its highly unlikely that it would be used. Here are the MKIIC+ schem's:

http://tubefreak.com/mk2c2.gif
http://tubefreak.com/mk2c.gif


The schematic's of the Studio, Quad, Mk3, Mk4 and MKV (IIC+ Mode) all show a 270k value for that resistor, also the MK4's lead circuit schem is IDENTICAL to the C+ modded Studio schem with exception to the 170k resistor in question.

I have read that the MK4's lead circuit is meant to be the same as the MKIIC+ and based on the component values shown, this appears to be 100% true. This leads me to believe that the stock 270k resistor is the correct value and does not need to be changed. Compare the C+ modded Studio schem to the MK4 lead circuit:

http://genitalhercules.com/~mcrowe/img/lead_C+mod.jpg
http://tubefreak.com/mk4-2.gif


Here is a link to the same Studio C+ Mod drawing that someone edited with some instructions, it might be helpful to anyone interested in doing the mod, but just ignore the 170k and keep the stock 270k:

http://voices.yahoo.com/converting-mesa-boogie-mark-iic-studio-preamp-3858698.html?cat=33#comments




mboogman wrote:
I'd be glad to help any I can. I haven't seen the insides of a quad before though. I can send you some pics of the inside of my Pre after the mods if you like.


Pics would be great thanks, maybe some close ups of the changed components? I have located all the parts to be changed on my Quad but just wanna make sure.


Cheers!

Shane

Author:  Caligulus Boogie [ Sun Jan 22, 2012 2:23 am ]
Post subject:  Re: Studio Premp w/ MKIIc+ mod

Forgive my ignorance, but does the deep mod and bass shift require a push/pull pot to be installed or is it a permanent "shift"?

Author:  mboogman [ Sun Jan 22, 2012 9:27 am ]
Post subject:  Re: Studio Premp w/ MKIIc+ mod

The 170k is indeed incorrect. I forgot to mention that. I'm trying to remember what I used, but i think it was a 470k. I'll have to give the 270k a try to see if it works better.

Author:  Shane C [ Sun Jan 22, 2012 8:18 pm ]
Post subject:  Re: Studio Premp w/ MKIIc+ mod

Caligulus Boogie wrote:
Forgive my ignorance, but does the deep mod and bass shift require a push/pull pot to be installed or is it a permanent "shift"?


Hey Caligulus, yea the idea is to make the studio have switchable options so its more like a standard Mark Head.



mboogman wrote:
The 170k is indeed incorrect. I forgot to mention that. I'm trying to remember what I used, but i think it was a 470k. I'll have to give the 270k a try to see if it works better.


Hey mboogman,

Didn't you have the 270k in there as stock? Bigger resistor = less gain and this will affect the tone slighty as well. Also you might want to try 1000pf instead of the 500pf off the top of V3b. That cap is basically interchangeable and Mesa played with it a lot!! Here are the most common values used by Mesa Boogie throughout the mark series amps (that I know of) for that particular ceramic cap:

No Cap (Blue & Green Stripe MK3, Quad Preamp - Lead 1, Studio Preamp)
500pf (MK4)
500pf (Red Stripe MK3)
1200pf (Quad Preamp Lead 2)
2000pf (MK3 Black Dot)



Shane

Author:  Caligulus Boogie [ Mon Jan 23, 2012 2:32 am ]
Post subject:  Re: Studio Premp w/ MKIIc+ mod

Any particular pots u recommend for this mod? Or any to just plain stay away from?

Author:  dtrax [ Wed Dec 06, 2017 12:10 am ]
Post subject:  Re: Studio Premp w/ MKIIc+ mod

Rather than start a new thread I figured I'd bump this one.

I just did a non-switchable "Bass Shift" mod - simply swapped C232 (V1a cathode bypass cap) from 15uf to .47uf. For anyone playing high gain metal this is a MUST HAVE mod. Stock, the SP can be dialed fairly tight, but that meant the Bass at 0 and mids below 3, give or take. Now you get a bit more mileage out of the Bass/Mid knobs, just the Mark amps. I'm actually surprised Mesa didn't include the Bass Shift option to begin with way back when.

Hardwiring it in is a sacrifice, however. The clean channel is a bit less bouncy, but still sounds fantastic. No sweat for me though, I bought it for high gain. Having a nice clean channel is just a bonus.

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