Buffers & the Mark II FX Loop

Pre Recto days. Boogie modified Fenders, Mark I-IV, Dual Calibers, etc

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Mark III
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Buffers & the Mark II FX Loop

Post by zebpedersen » Sun Jan 20, 2019 5:44 am

Wanted to gather some thoughts / experiences on the use of buffers and the FX loop of the IIC+

According to this article https://mesaboogie.zendesk.com/hc/en-us ... ects-loop- published by Mesa, all amps since the IIC+ have had a buffered FX loop, and therefore would *in theory* not suffer from any tone suck when running pedals in the loop.

My first question—does this apply to IIC+ upgrades? (My amp is an '83 IIC upgraded to a + at a later stage)

Secondly, I played a Mark IV for years and there was definite tone-suck in the loop (even though according to the Mesa article above the loop would have been buffered). Does anyone have any experience running a dedicated buffer (like a Stowaway) in the loop? Would this interfere with any in-built buffer circuitry the amp might have?
Mark I HRGX 15"

Mark III
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Re: Buffers & the Mark II FX Loop

Post by jrb32 » Wed Mar 13, 2019 6:20 am

My first question—does this apply to IIC+ upgrades? (My amp is an '83 IIC upgraded to a + at a later stage)
All C+ upgrades end up the same as all other C+s in the end from a circuit point of view and an FX loop point of view. Exactly the same. Anyone who says otherwise is misinformed.

The preamp circuit board may be different though. The RP10As were the original IICs. The RP11As were the late 83 redesigned IICs. The RP11A is the same board as the factory C+s and all factory C+s started off life as an RP11A (or SP11A for non reverb) IIC. It just happened that the + upgrade was done on the factory production line before the amps shipped out.

Regarding the tone suck on the IV I can't comment as I don't own a IV (yet)! Schematic wise the FX loop is identical in 'Normal' FX loop mode though in the IV and the IIC+ though. Hopefully that answers your question a little bit - I'm not an electronics designer or anything. Someone on here will be able to answer in more technical detail hopefully though.


Last edited by jrb32 on Thu Mar 14, 2019 4:22 am, edited 1 time in total.

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Re: Buffers & the Mark II FX Loop

Post by Thaymz » Wed Mar 13, 2019 11:55 pm

I never thought there was much of a difference.

Recently I started using the JP2C without FX loop and it definitely has a bit more bite and growl. Subtle enough that it’s probably not worth worrying about but it is there.

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