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previous: R.G. Not bad, Jeff. Just a couple of pro... -- 6/16/2000 1:43 AM

Re: Next Puzzler

6/16/2000 3:49 AM
Jeff	Re: Next Puzzler Hmmm.... I thought I copied your schematic correctly, but I might have swapped the diode directions. Should the bias current keep the diodes forward or reverse biased? I thought it was providing some reverse bias to make the diodes need more voltage to break over. Swapping their direction would mean less voltage, and eliminate the need for the 47k resistors. I was modifying this similarly to how you would modify an MXR Distortion+ into a TS-type feedback distortion. In the MXR, as in your mystery circuit, the diodes are connected from the signal to ground at the same point. In the feedback distortion, one end of the diodes hooks to the opamp output, and the other to the negative input. In parallel is a gain pot. This is what I have attempted to do here -- hook one side up to the opamp output, and the other to the negative input except I have inserted BFCs to eliminate the DC path. The current mirror providesthe bias current. Look again -- the two 100ohm resistors do hook to a BFC to the negative input of the opamp. I have also added a dual current-mirror that balances the voltages better. It still has the diodes the same direction as the original and still no values. http://members.aol.com/jeffhailey/mystryfb2.gif -Jeff

6/16/2000 3:49 AM

Jeff

Re: Next Puzzler

Hmmm.... I thought I copied your schematic correctly, but I might have swapped the diode directions. Should the bias current keep the diodes forward or reverse biased? I thought it was providing some reverse bias to make the diodes need more voltage to break over. Swapping their direction would mean less voltage, and eliminate the need for the 47k resistors.

I was modifying this similarly to how you would modify an MXR Distortion+ into a TS-type feedback distortion. In the MXR, as in your mystery circuit, the diodes are connected from the signal to ground at the same point. In the feedback distortion, one end of the diodes hooks to the opamp output, and the other to the negative input. In parallel is a gain pot. This is what I have attempted to do here -- hook one side up to the opamp output, and the other to the negative input except I have inserted BFCs to eliminate the DC path. The current mirror providesthe bias current. Look again -- the two 100ohm resistors do hook to a BFC to the negative input of the opamp.

I have also added a dual current-mirror that balances the voltages better. It still has the diodes the same direction as the original and still no values.

http://members.aol.com/jeffhailey/mystryfb2.gif

-Jeff