Fx loop mod question (F50, Nomad, Rectoverb)

[fabien]

Hi all,

I've got a tech question about the infamous parallel to serial fx loop mod that I plan to make on my F50.
Now this is the normal loop:

This is the classic mod taking the mix pot out of the circuit:

This is a variant I found here on this forum (concernig a Nomad IIRC). It leaves the mix pot in the circuit as a level return:

Now this is a cable solution presented by HAL9000 on the F50 massive thread on HC forum:

the principle beeing to ground the loop signal via the mix pot acting as a master volume.

The question is: is the variant correct (without grounding the signal or should the third pot log put to ground (like in the cable version) as in here:

I hope I'm beeing clear enough.

Cheers
Fabien

 

[mr_fender]

In order to function as a real volume control, the other side of the pot would have to be grounded. The jack trick will work but you can no longer use the loop for effects. If you do the serial mod and ground the other side of the pot, you'd still have a normal serial loop plus an extra master volume. However, I believe the mix pot is a linear taper pot, so using it as a volume control will be a bit screwy. All of the volume change will take place in just 10-20% of the pots rotation. Without a logarithmic taper pot, volume control will be tricky. You wouldn't have a gradual sweep of volume on the pot. If you're converting the loop to serial, another option would be to make a little master volume box to go in the loop that has a proper logarithmic taper pot. I use a volume pedal in the loop of my Mark IV for swells and it works great. It's nice to have a quick way to mute the amp on stage too for tuning, switching guitars, etc.

 

[fabien]

Thanks for your reply. I use the cable trick when I don't use my G-Major and it works great, the mix pot works as a master and is quite 'linear' in its behaviour so it should work ok with the serial loop too.
I plan to contact Mesa before doing the mod to see what they say anyway. Always wondered why they didn't build a master volume (called output on the Nomads and the MKIV I believe) into the F series (and Express).

 

[nomad100hd]

why do you need the mix knob to be another master volume? Sounds like someone smoking something. I only need one Master Volume. I found no reason to leave the Mix knob in the circuit when i did my parallel to Series mod.

 

[fabien]

why do you need the mix knob to be another master volume? Sounds like someone smoking something. I only need one Master Volume. I found no reason to leave the Mix knob in the circuit when i did my parallel to Series mod.

The F50, unlike the output control on the Nomad, does not have a global output level control, only the two channel master. So to raise the volume of the amp you have to tweak both channel master wich can bring the channels out the level balance you had. At lower volume it's almost impossible to keep the balance right in one go, you need several tryings for that.
Not a major drawback but if it can be easily helped with the mix pot...

 

[Koreth]

In that case, it may work, but since the mix level pot is a linear pot, it probably won't be ideal, as previously mentioned.

 

[nomad100hd]

anyone though of just drilling a hole in the chassis and adding an MV?

 

[fabien]

In that case, it may work, but since the mix level pot is a linear pot, it probably won't be ideal, as previously mentioned.

The pot behaves fine with the cable trick, I don't see any reason for it to behave differently when hardwired to groud.

 

[Charlieratz]

In order to function as a real volume control, the other side of the pot would have to be grounded. The jack trick will work but you can no longer use the loop for effects. If you do the serial mod and ground the other side of the pot, you'd still have a normal serial loop plus an extra master volume. However, I believe the mix pot is a linear taper pot, so using it as a volume control will be a bit screwy. All of the volume change will take place in just 10-20% of the pots rotation. Without a logarithmic taper pot, volume control will be tricky. You wouldn't have a gradual sweep of volume on the pot. If you're converting the loop to serial, another option would be to make a little master volume box to go in the loop that has a proper logarithmic taper pot. I use a volume pedal in the loop of my Mark IV for swells and it works great. It's nice to have a quick way to mute the amp on stage too for tuning, switching guitars, etc.

 

[Charlieratz]

Hi. I tried the mod with a cable where one side is grounded and it worked a great so i then tried to rewire the pot so i still have the use of my fx loop and it didn’t work. Can you help please ??