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PostPosted: Sat Dec 24, 2011 3:54 am 
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Mark I

Joined: Wed Jun 15, 2011 1:36 pm
Posts: 50
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!

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Road King Series 1 combo
Stiletto Ace combo
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Zilla custom fatboy 212
Egnater Rebel 20
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PostPosted: Fri Dec 30, 2011 6:35 am 
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Mark II

Joined: Sun May 28, 2006 12:09 am
Posts: 58
Location: New Zealand
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

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Current Gear:
Quad+ Preamp
MK IVB+ Combo (sold)
Egnater IE4
VHT 2502
TC G-Major 2
ART EQ351
Korg DTR-2000
RMC3 Wah
Voodoo Labs Ground Control and GCX Switcher
Marshall 1966b 2x12 with G12-65's
Ibanez RG1550 with Bill Lawrence pups


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PostPosted: Sun Jan 22, 2012 2:23 am 
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Bottle Rocket

Joined: Sun Jan 22, 2012 2:18 am
Posts: 2
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"?


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PostPosted: Sun Jan 22, 2012 9:27 am 
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Mark I

Joined: Thu Nov 03, 2011 9:09 am
Posts: 33
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.

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Mesa Boogie Studio Preamp w/MKIIc+ mod
Egnater M4 w/ Xman, EG5, VX, EG3 mods
VHT 2:90:2 power
Lexicon MPX-G2
TC Electronic GMajor
Digitech IPS33b
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PostPosted: Sun Jan 22, 2012 8:18 pm 
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Mark II

Joined: Sun May 28, 2006 12:09 am
Posts: 58
Location: New Zealand
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

_________________
Current Gear:
Quad+ Preamp
MK IVB+ Combo (sold)
Egnater IE4
VHT 2502
TC G-Major 2
ART EQ351
Korg DTR-2000
RMC3 Wah
Voodoo Labs Ground Control and GCX Switcher
Marshall 1966b 2x12 with G12-65's
Ibanez RG1550 with Bill Lawrence pups


Last edited by Shane C on Thu Aug 07, 2014 3:00 pm, edited 2 times in total.

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PostPosted: Mon Jan 23, 2012 2:32 am 
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Bottle Rocket

Joined: Sun Jan 22, 2012 2:18 am
Posts: 2
Any particular pots u recommend for this mod? Or any to just plain stay away from?


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PostPosted: Wed Dec 06, 2017 12:10 am 
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Mark II
User avatar

Joined: Tue Feb 26, 2008 2:23 am
Posts: 56
Location: West Chester, PA
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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Guitars:
Ibanez '98 RG7620 (EMG 81-7H, 60-7H)
Amps:
Triple Recto 3CH, Studio Preamp, 2x12 Recto Vertical cab
Past:
Mark V head, Rectoverb series 2 combo, F-30 combo, V-Twin rack pre


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