Mark IIb Post FX LVL

[JAMz]

Does any one knows the details of what this mod is all about? Also can anyone name the brand that mesa was using or is still using as for filter caps particulary in the pre-amp section and good replacement optios?

Thanks,

 

[Boogiebabies]

What mod?

The 30uf / 500V filter caps were Sprage Atoms made for Mesa.
If your talking about the cathode caps, some older ones had 15V electrolytics and around the MK II they used tantalum and hermetically sealed tantalums which were all probably made by Kemet and are still available from Mouser.

 

[Dutchman]

I don't know all of the details of the mod, I do know it is $250.00 cashiers check to Mike B. When completed the effects loop is supposed to be more friendly with different foot pedals and other effects as far as the signal strength. The tone is also to show some improvement and the Reverb is also improved. Nothing wrong with Mike B. checking your entire amp over either.

You have to contact Mesa for a R.A.

My Mark IIB does not demonstrate any of the issues that the mod would fix. However it does not have the effects control knob either. Just the presence and Reverb controls. Mesa was unable to check back far enough to see if they had worked on it.

Mesa does have records going back aways, so you might be able to find out if they have done yours already. They started doing the mods shortly after the IIB amps came out but didn't keep records till later.


This copy and pasted from

http://homepage.mac.com/mesaboogie/IICPlus.html

With the Mark IIB, unlike the Mark IIA, it had the junction to the Pre-Amp/Pwr Amp only on the underside of the amp. The rear panel now had a true effects send and return. next to the Slave Out jack. The IIB however had well known "issues" with this effects loop. It tended to overdrive effects when switching into lead mode, and the reverb level in lead mode was markedly decreased. Mike B. and Randy came up with a fix which lead to the effects loop mod for the IIB. It added a fourth master that allowed the effects and reverb levels to be properly balanced. However, it does change the lead sound. The mod gave the IIB a more IIC+ lead tone which is great, but very different from the IIB sound which had a compressed, less gain sound as a result of the "bottle neck" between the pre-amp and the power amp section.




Others with the IIB have been very happy with the results of this mod.
Mine sounds awesome!!!!!

 

[JAMz]

Thanks for the replies. My IIb has the "POST FX LVL" mod. I was wondering how this mod affects a stock IIb, I could not tell the diffrence since I got mine already modded. Thanks for the input!

Regarding the filter caps....My amp was service by a local tech back in '92. I guess it was him who replaced the filter cap that is located in the first pre-amp stage with a goofy "sky" cap. I found the replacement alreday in thetubestore.com "Sprage Atom". I also noticed that the amp has three other 30uf 500v caps in the power section with "mesa" printed on them. I guess I shall call boogie monday and find out if they have this replacement cap. Thanks for the help,

JAMz

 

[JOEY B.]

I have a 1978 Mark I that Mike put a true effects loop into. The send and return jacks replace the slave out and power amp in jacks on the rear panel. It has the Post FX Level knob where the slave knob used to be. He explained that this knob controls the amount of preamp signal that is fed to the power section. My amp now acts like a Mark IV, with the front panel master vol. acting like an effects send and the rear panel knob acting like the effects return pot or Output level controller the Mark IV. It does this with or without anything plugged into the loop. It might change the sound some but I have always been happy with it.

 

[Boogiebabies]

Thanks for the replies. My IIb has the "POST FX LVL" mod. I was wondering how this mod affects a stock IIb, I could not tell the diffrence since I got mine already modded. Thanks for the input!

Regarding the filter caps....My amp was service by a local tech back in '92. I guess it was him who replaced the filter cap that is located in the first pre-amp stage with a goofy "sky" cap. I found the replacement alreday in thetubestore.com "Sprage Atom". I also noticed that the amp has three other 30uf 500v caps in the power section with "mesa" printed on them. I guess I shall call boogie monday and find out if they have this replacement cap. Thanks for the help,

JAMz

Mesa still uses these caps in their production amp. They are not Sprague anymore. They are stamped Mesa 30uf / 500V, but they are made by United Chemi-Con. The same applies for the 220uf / 285V caps.

 

[JAMz]

In your opinion, is there a difference between the sound of the United Chemi-Co and the Sprague Atom?

 

[Dirt123]

I have a 1978 Mark I that Mike put a true effects loop into. The send and return jacks replace the slave out and power amp in jacks on the rear panel. It has the Post FX Level knob where the slave knob used to be. He explained that this knob controls the amount of preamp signal that is fed to the power section. My amp now acts like a Mark IV, with the front panel master vol. acting like an effects send and the rear panel knob acting like the effects return pot or Output level controller the Mark IV. It does this with or without anything plugged into the loop. It might change the sound some but I have always been happy with it.

Does Mike have to add any tubes or other circuitry to the amp, or is he just adding another pot?

 

[RR]

Others with the IIB have been very happy with the results of this mod.
Mine sounds awesome!!!!!

Yup, I got the same or similiar mod. Actually I was having my Mark IIB serviced and Mike B. asked me if I wanted this modification. I said 'Yes'. I was very pleased with it. I don't use stomp boxes but I do use a digital delay unit and it works great.