Problem understanding Gretsch Controfuzz schematic (GGG)

I've done a PCB for this schematic: http://www.generalguitargadgets.com/pdf/ggg_controfuzz.pdf
And is not quite working, I've made sure everything was correctly connected and also that there are not any missconections made with solder.

On the output it sounds as what I think is a booster, when you turn on the potentiometer the volume gets higher and there is distortion when going too far (I am using a 25K pot instead of 10K) but the GAIN pot doesn't do anything.
When probing pin 1 of the TL072 I can only hear a high pitched noise, I think the problem is coming from there. Is the same noise I get from DC, which I can see that is connected to the input and then to pin 3 and don't understand why.
Why to send DC to the TL072 input:?:

This circuit is supposed to mix the fuzz signal with the dry signal, so I think that GAIN is more like MIX.

Any ideas??? Thanks!

When probing pin 1 of the TL072 I can only hear a high pitched noise, I think the problem is coming from there.

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These may be parasitic oscillations. It is a typical problem when operating an op amp at high gain.

There are a number of things to try in order to eliminate them. Connecting a resistor or capacitor at various points around the op amp, etc.

Why to send DC to the TL072 input

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The join at R1 & R2 sets a volt level halfway between 9V and 0V, so the op amp can provide an output swinging up and down inside that range.

but the GAIN pot doesn't do anything.
...
This circuit is supposed to mix the fuzz signal with the dry signal, so I think that GAIN is more like MIX.

Click to expand...

Pot 1 appears to mix dry and fuzz waveforms.

Pot 2 only attenuates the output. Is that the one that does not seem to do anything?