Re: offcenter virtual ground, opamp mic with transformer
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The other things that may be going on are secondary virtual ground conductance passes that affect the two 47K resistors, the transformer, i don't?know exactly. The virtual?ground works?well with AC sources as in the signal going through the Op Amp but if something affects the DC bias it shifts, which is what we are seeing here.?
Jules??
"I have successfully used the VSSOP version. I have the PCBs assembled (PCBWay) and have not had issues. I am also using SMD 1G and 500M resistors. I feel like there is something else going on here."
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What makes you think there is something else going on, if I may ask?
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Your PCBAs were soldered by PCBWay, and they most likely applied stencil printed solder paste and reflow soldering. At least, that is what I think was done with PCBAs that PCPWay assembled for me. That process leaves only a very small amount of flux residues on the PCBA. Much less than most people will be able to achieve when manually soldering.
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Secondly, when manually soldering, the odds that flux residues will get charred or desintegrate into components that are somewhat hygroscopic and conductive are much higher than in the case of a well-controlled reflow solder process. It very much depends on your temperature settings, solder iron, solder + flux type and your solder skills.
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Jan
-- Best Regards,
Jules Ryckebusch
214 399 0931
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