Please help me understand the Mark IVa fx loops

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

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Bottle Rocket
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Joined: Mon May 01, 2017 8:03 pm

Please help me understand the Mark IVa fx loops

Post by elegost » Sat Nov 11, 2017 6:55 pm

Ok, please help me understand the weirdo setup on the Mark IVa.

There are two sets of fx loop jacks, one set called "normal" and the other called "switchable".

There is a rocker switch that lets you select Normal or Switchable.

Testing shows that the normal and switchable jacks cannot be active at the same time.

Am i correct about how this is supposed to work? If that's the case why did they even bother putting two sets of jacks in the thing?

I guess what i find really confusing is that the manual says "Effects Loop Selection of the Mark IV is quite sophisticated, offering two loops, and a selector switch. The loop labeled "Normal" stays on all the time. The other loop is switched In or Out of the circuit by either the FootSwitch, the programming rocker switches, or the External Jacks (when the Mark IV is being controlled by a MIDI switcher)."

To me, "two loops" with one that "stays on all the time" implies that there are TWO LOOPS, i.e., you could put a reverb in the normal loop and it would stay on all the time, while you switched a delay in and out of the other. But from testing with the amp it looks like there are basically two sets of jacks for one loop. If you plug into the the normal set it ignores the footswitch. Plug into the other set and get the option to switch on and off.

Do i have it right?

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Mark III
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Re: Please help me understand the Mark IVa fx loops

Post by swbo101 » Mon Nov 13, 2017 1:49 pm

I never tried to plug into both at the same time, but I've noticed that depending on how the rocker switch it set, that makes the appropriate jacks active.

Yeah, a bit misleading.
1991 Mark IV A

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