Hello all, I don't normally post here much but @thet is there a specific reason why the transformer primary needs to use virtual ground versus "original recipe" ground at pin 1? I can guess we're able to skip a DC coupling cap with your current schematic. Some transformers have gapped lamination or insulation between the windings to help with DC voltages like a HIPOT transformer. This may be a clue as to what's happening when you tried various transformers previously.
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My tinker fingers suggest using a DC coupling cap after the opamp U1-A output to the TX and using original ground at the primary from XLR pin 1 to see if you get virtual ground to behave again. Worth a possible lashing lol
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As well, transformers present inductance, capacitance and most importantly a resistance (DCR). No two transformer companies truly approach ratio vs DCR the same, my own company included. A Jensen 1:1 vs a Cinemag vs a Sowter will show different statistics and approaches to the same concept. This is what makes them all special.? That's the mystical art of designing iron. But despite these differences, we? still follow the laws of physics. So in simple terms imagine having a 240 ohm resistor to ground vs a 35 ohm resistor to ground on a load line that's sensitive to those resistances.? That's part of what we experience when using varuous 1:1 transformers. I would be highly interested in the DCR numbers on the transformers that behaved vs ones that didn't. DMM set to proper resistance range, between the input pin on the primary and the "ground" pin you're using, may be worth checking the secondary side as well.
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Glad to help throw spitballs at the board with you.?
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Thanks
-L.?
