Here is some more info. The basic DI circuit is nothing more than a buffer and a final gain stage that has an extra opamp that takes the output and inverts it to provide the extra output needed for the balanced XLR jack. I used the basic circuit that Jack Orman published.
Then I added these features as options: Switch for -15dB input pad, High cut filter, input attenuator pot, -15dB output pad switch, phase invert switch, output level pot, ground lift switch, Marshall 4X12 cab sim switch, bypass 1/4″ jack, Inverted out unbalanced 1/4″ jack, normal out unbalanced 1/4″ jack, balanced out TRS 1/4″ jack, balanced out XLR jack.
I did not add a phantom power switch but that is possible. I used a smaller vero for the cab sim circuit and a larger one for the rest of the design.
I made one of these for a local club sound man. I hope this helps inspire builders!
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