Using a single supply and the circuit as shown in post #1 try a simple bias on the TL072 like this. Input and output coupling caps are required to block the dc voltages....the only thing that seems to work is to feed the signal into the noninverting input, plus add a 1M resistor which is connected to my Vdd/2 rail, and remove small 10p cap to ground at the input. The C3/R3 II C7R7 filters are extremely important, to the overall tone..C7 is .15u so I had to wrap a couple caps in paralell to get close to that value. Its definitely in the ballpark of the sound I've heard on vids of the MG10..got that Marshall growl.
SG
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