Burr Brown OPA 2143 vs NJM2068

Typical bias current for LM4562 is 10nA. Taking into account possible unbalance of 10k we get 0.1mV unbalance.

Good, keep going. Calculate the effect of the input offset current based on the higher of the two source impedances, and add that. Then add the input offset voltage. Then multiply by the the sum by the DC gain of the circuit . . . you now have the number you're after. A mV or two of offset gets pretty scratchy-clackety on the source-selector and volume controls of a following preamp (provided they're DC coupled).

Again, it COULD work fine if you change to DC output coupling to accompany your opamp sub (10nA is pretty low for a bipolar opamp) . . . but like any modification, a full analysis of the particular circuit as it pertains to your particular mod is required if you want to be confident of a positive outcome.

Input offset current is 11nA typ and offset voltage 0.1mV. Total of 0.3mV giving generous 10k unbalance. Gain after DAC is practically none. Sub 1mV offset might be a problem for some power amps but not for mine (5Hz-65kHz).

Kijanki, the technician knew that the AD818 is a video amp. He uses it on purpose because he says it´s faster. I´ll talk your recomendations with him. I suppose the decision of which one to use will be taken once he opens the poweramp and sees what the circuit is like. Thanks again!