OpAmp Oscillation Trouble

[seedlings]

I had this circuit breadboarded to tweak, and got it sounding how I wanted.  Soldered up to breadboard and found a super high-pitched oscillation.  It gets progressively louder as the 100K gain pot is increased.  I breadboarded with 9V, then switched to the 15V notebook supply indicated.  So, I switch back to the breadboard 9V power supply and the oscillation persists.  I tried a 1000uF in parallel with the 100uF and that was a very marginal improvement.

When I unplug the input cord from the guitar it screeches like a banshee.  I'm using the same test jack setup as when it was breadboarded.

I inspected and tapped on all the solder connections with no change.  Tried caps across the clipping diodes.  Tried larger cap where the .01uF on V1b feedback loop.  Tried cap across 1M ground.  Tried an additional 1M to ground on the other side of the 10uF input cap.  Tried a cap in the V1a feedback loop.  Ground the input and problem goes away.

Fellas, if you see anything awry in this simple circuit, let me know.



CHAD

[amptramp]

The ground on the bottom of the 1M input resistor should be cut and connected to B++, the half voltage supply.  The B++ connection at the top of this resistor should be deleted.  You may need a capacitor across the 1K feedback resistor in the first stage to tame it as you will get excess phase shift where the rising characteristic of the closed loop gain intersects with the falling characteristic of the op amp.  You may need bypass capacitors that are better than electrolytics.  I would suggest a film capacitor across the 100 µF to eliminate high-frequency feedback through the power supply.

[seedlings]

Aargh... there is actually a 470K to B++ instead of a direct connection, but the 1M should be removed from the circuit, thank you.  I'll start with that and add your other suggestions one at a time.  Thank you.

CHAD

[seedlings]

It was the 1M on pin 3 to ground.  It was supposed to be before the input cap.  Thank you amptramp!

CHAD