The circuit shown in bottom figure in jackinnj's post - the one with a 100 ohm resistor across the differential input of the LM3886 - does work. It provides an amplifier with good stability and reasonable phase margin, but at the expense of lowered loop gain.
See Sergio Franco, "Design with Operational Amplifiers and Analog Integrated Circuits", 3rd ed. Fig. 8.24.
Rather than blow the loop gain at all frequencies, one could consider input-lag compensation - i.e. insert a capacitor in series with that 100 ohm resistor. That way the amp has max loop gain from DC up to the zero formed by the input RC. But as twest820 points out, one has to be careful with the input capacitances (including stray cap).
~Tom
See Sergio Franco, "Design with Operational Amplifiers and Analog Integrated Circuits", 3rd ed. Fig. 8.24.
Rather than blow the loop gain at all frequencies, one could consider input-lag compensation - i.e. insert a capacitor in series with that 100 ohm resistor. That way the amp has max loop gain from DC up to the zero formed by the input RC. But as twest820 points out, one has to be careful with the input capacitances (including stray cap).
~Tom
You're referring to the MyRef rev B and related variants? I'm not up on all the flavours---I seem to recall MyRef going to rev F, along with the MiniRef some others---but the rev B operates the 3886 at about 18dB local gain with the input lag compensation tomchr mentions. It has an overall closed loop gain of 30dB, which is a bit higher than unity.
If memory serves, tomchr worked up a unity gain input lag configuration a few years ago. What we ended up finding was applying sufficient compensation to stabilize the 3886 at unity resulted in audible phase shifts. The MyRefs only phase by 5 degrees or so as the local gain allows lighter compensation but I haven't looked at the circuit enough to assess the risks around its use of positive feedback. Component tolerance analysis seems particularly worthwhile.
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