F-50 Parallel to Series Loop mod (revisited)

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knightage

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Hi All,
I'm using a Line6 M13 into my F-50, using the 4 cable method. Basically with Filters, and Distortion models straight into the amp, and Mod/Delay effects in the loop. But, there are 2 things that are happening. With the FX mix knob @ 50%, it sounds like I'm getting some comb filtering. It seems to go away when I'm at minimum, obviously, and at max. But there's also a hum that's coming through. When I run straight from the M13 into the F-50, no loop, no hum. I read through some forums, and it seems that the comb filtering has to do with the A/D/A creating a phase issue, and a loss of volume and tone.

I found a post from a while ago (2005) about modding the F-50 FX loop from parallel to serial. The poster is referring to Mesa Support:

I called their customer support and they quickly sent me a diagram on the change to the mix pot wiring, to make the loop serial.

Basically there are three wires that go to the three lugs on the mix pot. For the mod, you

-disconnect the 1st wire on the left (looking down onto the pot with the knob pointing down and the lugs up) and connect it to the middle lug (along with the middle wire that is already connected there)

-disconnect the 3rd wire which is on the right


There were some other mods for nomads that were basically the same, but instead of soldering back to the pots, they just disconnected the wires entirely from the pots, jumped wires 1 and 2, and insulated them?

My questions are:

Has anyone done this? Results?
Is this my solution for my current set-up? Solving the phase/combing issue?
Does the pot retain some function, i.e. send level, if you don't disconnect the wires altogether?
Could this resolve the hum issue as well?

Thanks!

Eric.
 
knightage said:
My questions are:

Has anyone done this? Results?
Is this my solution for my current set-up? Solving the phase/combing issue?
Does the pot retain some function, i.e. send level, if you don't disconnect the wires altogether?
Could this resolve the hum issue as well?

Hi All,
I've actually done the mod to my amp. It was actually very easy. I'm happy with the results, and because it's such an easy mod, if I went with an effects unit better suited to a parallel loop, It's easy to switch it back. I'm actually looking for a schematic to make it switchable. I'll answer my own questions for anyone who is interested.

The mod was easy. The results so far are really good. I don't notice a huge difference in tone. I had some recordings from before the mod, and after. I noticed a "slight" drop in the high end. But since I was always trying to tame the high end a bit, this wasn't a big deal for me.

It was definitely the solution no more phasing/combing issue.

The mix pot has no function now. There would have been no difference with disconnecting the pot altogether. I'm trying to find a way to replace the pot with a push/pull that will make it switchable between a series and parallel loop. Still trying to work that out.

I actually isolated the hum issue. It didn't have to do with loop, but the recording out which I was using to feed the PA for rehearsal. Fixed :)
 
knightage said:
I actually isolated the hum issue. It didn't have to do with loop, but the recording out which I was using to feed the PA for rehearsal. Fixed :)

Ground loop hum? DI box with ground lift fix the issue?
 
MusicManJP6 said:
Ground loop hum? DI box with ground lift fix the issue?

It must have been a weird ground loop. It actually modulated, no effects on, if that makes sense. I just plugged my amp and fx unit into the same panel as the mixer, and it went away.
 
knightage said:
MusicManJP6 said:
Ground loop hum? DI box with ground lift fix the issue?

It must have been a weird ground loop. It actually modulated, no effects on, if that makes sense. I just plugged my amp and fx unit into the same panel as the mixer, and it went away.

Yep... that's a ground loop. If you plug up all your gear to the same outlet then they all use the same ground. When you use a different outlet for even one of those pieces of gear then you introduce a ground loop. :)
 
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