Problems with R.G. Keen's Simple Easy Parametric EQ

[AndrewCE]

My current build is R.G. Keen's "Simple, Easy, Parametric EQ"; it seems so elegant and it's exactly what I need (not to mention parametrics on the market are WAY too expensive).
http://www.geofex.com/Article_Folders/EQs/paramet.htm

The problem is, it doesn't seem to want to work.
I built it on protoboard, and the guitar signal went straight through it, seemingly unaltered. When I turned the knobs there was no effect. The only things I did different from the schem are: I only made one band of filtering (instead of 2) and I used a 2.2uF input cap instead of 1uF.
I should also mention that the thing oscillates when the Q knob goes below a certain level. Sometimes it oscillates straight away, and sometimes it only starts it when I hit a hard note. The frequency of the oscillation seems to be directly controlled by the freq knob. The only way to stop the oscillation is to twist the knobs until it stops.

I took the circuit apart and rebuilt it, and found the exact same problems.

Any ideas on what I've done wrong?

-Andrew

[AndrewCE]

I thought the problem might be that one of my 3 op amps was in a dual-package TL072, the other opamp of which was unused. So I connected the + to the - of that extra opamp, and shorted the output to ground. But, no success, the circuit is still useless (no EQ effect; instead, oscillations).

I'm just astounded at how simple this circuit is, and at how hard it is for me to debug...

[R.G.]

Read "What to do when it doesn't work" and give us some info.

[AndrewCE]

Agh I just moved back to school... I'll get the voltages to you at the start of summer break. They all seemed normal when I checked them though (don't worry, I wouldnt have posted without checking the debugging page first )
I was just wondering if you would maybe recognize the problem (filter wreaking havoc as an oscillator) as a common one in a circuit like this. If not though, I'll get the voltages when I can.

[R.G.]

Agh I just moved back to school... I'll get the voltages to you at the start of summer break. They all seemed normal when I checked them though (don't worry, I wouldnt have posted without checking the debugging page first )
I was just wondering if you would maybe recognize the problem (filter wreaking havoc as an oscillator) as a common one in a circuit like this. If not though, I'll get the voltages when I can.

Sorry, I don't recognize it as a common problem. Filter circuits, especially gyrator based ones, can be tricky.