Recto Recording Preamp Series Loop Mod

Triaxis, Quad Preamp, Stereo Power series, Recto Preamp

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Steve Hunter
Bottle Rocket
Posts: 1
Joined: Sun Dec 23, 2018 11:30 pm

Recto Recording Preamp Series Loop Mod

Post by Steve Hunter » Mon Dec 24, 2018 12:26 am

I took the plunge today and did the mod to change the parallel fx loop to series on my recto recording preamp. It was pretty different from the dual rec mod to do the same thing which I've seen pictures of, but fortunately those gave me enough of an idea that I was able to figure it out, thanks also to Mesa for labeling their breadboards really well. So here are some pics.

My reason for doing the mod was that having just purchased a Boss ES-8 loop switcher/midi controller/amp controller everything was going along fine until i tried using certain combinations of pedals and found I got the low frequency hum people talk about which is apparently caused by the phase shift between the dry signal being mixed with the wet signal, and others have reliably solved the same problem on Dual Rectifiers by converting the FX loop to series instead of parallel - a shockingly easy, reversible mod. This was a little tricky for me to figure out because the layout is different, so I couldn't just copy what the others did, and there are stereo returns instead of just a single one. Beginner's luck i guess, cause it worked first try and went off without a hitch.

Step 1: Clip off that potentiometer, from the "mix" knob that goes from 10% - 90%.
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Step 2: Clip off those 4 pink wires that went to the mix pot. Here you can see my testing phase, pre-solder. The Yellow and Brown wires are carrying the hot signal from the returns Left and Right back to the rest of the circuit (the next picture shows the other end of those, where you can see them labeled L and R).
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Step 3: De-solder the loose ends of the pink ones, and solder the Yellow and Brown wires into the proper places (Y=Left, B=Right), which are the two spots closest to the removed knob/pot.
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Having done this,I put my rig through its paces with the pedals that were causing problems before all on in various combinations and orders in the FX loop, and couldn't make the problem I was having before happen again, so I call that success!

Hope this helps anyone else considering this mod. I have about 5 hours of soldering experience in my life, a middle school elective course on electronics 23 years ago, and a general understanding of how to wire up a stereo. This mod really was that easy.

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