Phase 45 Mix Pot Mod

[p_wats]

Hey guys,

I'm just about finished populating a GGG Phase 45 board I had kicking around and wanted to do some of JC Maillet's Univibe mods. My issue at the moment is that I can't seem to figure out where on the GGG layout to wire in the 22K mix pot he suggests.

Looking at both JC Maillet and GGG's schematics I would have to guess the mix pot goes in place of R9 and R10, but I'm not quite sure about that (as I have no idea what I'm doing when it comes to schematics).

Can anyone point me in the right direction of what components I would remove if need be and where the mix pot would be wired in?

[Processaurus]

You're right, it replaces R9 and R10, you are replacing those resistors with a pot, and the wiper goes where they met, so essentially by turning the pot you are making one resistor bigger and the other smaller.  Any 5k to 50K (linear taper) pot should work fine.  It is a good mod, I did it on mine along with the univibe cap mods, and it seems to have a musical sound.

[p_wats]

Excellent! Thanks so much for the quick reply. This is one of the first few times I've read a schematic and made the right decision. Ha.

I'm looking forward to this. I'll probably do the Univibe switch and externalize the bias pot too. I'm not exactly sure what mod #4 does (the two resistors in series). Maybe I'll try it out.

I did a Phase 90 clone recently with a feedback pot and double vibe switches (one toggle for each pair of phase stages) and it sounds excellent.

[Processaurus]

The 2 resistors in parallel is just to get a 4.1K resistor, and odder value than 8.2K.

I remember the external bias pot being handy too.  It might travel too far, might want a trimpot inside to limit the range of the external pot's adjustment.

[p_wats]

Alright, so I populated the PCB (GGG version) and have been messing around with the mods prior to wiring the whole thing together. Here are my first impressions:

1) Mix pot is great. Allows me to go from clean to phase to vibe.

2) External bias is worth checking out, but I doubt I'll use it much as an actual knob, so I may re-internalize it for now.

3) Vibe toggle doesn't seem to have any effect. I may have wired it wrong, but the mix pot produces much more evident vibe tones regardless of which way the switch is set. Does that make sense?

Oh, and I also had to flip the transistors from the way the layout suggested to get any effect.

[p_wats]

Thanks for all the help guys! I got this one "boxed" up last night and it works perfectly: Volkswagen Phase 45 with mix pot and vibe switch:

[Processaurus]

Nice work! The pleasure was ours.

[p_wats]

Nice work! The pleasure was ours.

Ha. I guess I shouldn't really have pluralized that, as it was just you, Processaurus. Thanks!

[sckoci]

I just stumbled across this thread and had a question about your mods...

I have a GGG Phase 45 too and was wondering  what caps did you change to get the vibe effect?  C3 and C4?  I've looked at the schematic but I'm not too good at reading them.  Any help would be much appriciated.

[Processaurus]

Here's JC's website, there's some great articles, including the great P45 mods:

http://www.lynx.bc.ca/~jc/pedalsPhase45.html

That's your mod up at the top of the schematic, with the DPDT switch that changes between the pairs of .01 and the .047 caps.

EDIT: C2 and C3 on the GGG scheme