Clean blend pedal noise

[patrick398]

Hello all,
Just finished building a few pedals including a clean blend (schematic: http://jmkpcbs.com/wp-content/uploads/2014/03/Clean-Drive.pdf) using this vero layout:

I noticed something strange though. When i have a pedal in the loop, say a fuzz or overdrive, it introduces a lot of noise. I guess you'd categorise it as hum more than anything else. Obviously it gets more pronounced when turning up the volume or gain of the pedal in the loop and is worse with fuzz. Even when the effect in the loop is bypassed though there is still hum, it disappears with the blend pot rolled all the way back and gets worse the nearer 100% blend you get. None of these things surprise me to much but i'm stumped as to where the noise is coming from. All the pedals are pretty silent on their own, especially the fuzz which is a DBA harmonic expander and is super gated.
Any thoughts?
Thanks a lot

[GGBB]

What are you using for power? That circuit has no power filtering - any noise from the power supply will get added to the signal.

[patrick398]

Ah yeah good shout. I'm just using a regulated 9v power supply, i think it might be an EHX one but can't remember. Has always been totally silent with all my other builds so i'll try add some power filtering. Would a 100u across the rails suffice?
Thanks!

[GGBB]

That plus a 100n MLCC.

[Kipper4]

+9v>schottky diode >series 100ohms> 100uf to gnd>100nf to gnd.

Fancy Lime does a similar thing top left here

[patrick398]

Brilliant, thanks guys