Burr Brown OPA 2143 vs NJM2068

Change to LM4562 and you might be able to remove this cap.

With emphasis on "might", like in bold print, or a big neon sign. The LM4562 is indeed a good sub candidate for the 5532, even though it's not for the TL072. And the 5532/5534 is definately not known for its DC performance -- I agree that most newer designs are much better.

But the input bias currents of these medium-impedance bipolar opamps are far from negligible, and it is extremely rare to find balanced DC impedances in an audio opamp circuit that features an output capacitor - and this is what to look for (in addition to low DC gain) if you're planning on removing this capacitor in a circuit without a DC servo.

I take it you're fond of this part for its sound quality . . . maybe I'll have to add it to my list of things to play around when I have some time.

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

LM4562 has excellent AC characteristics but the sound is what matters. Benchmark uses it as a driver for XLR outputs because of the ability to drive 600 ohm (not necessarily because of sound). Getting rid of output cap would be a good thing but my Benchmark is still under warranty. NE5532 has bad rap on DIY forum - perhaps because it is so cheap. Somebody tried already replace NJM2068 with OP2132 and complained about metallic sound.

I do not have experience with LM4562 so I would not push for replacement of OPA627 or OPA2134 but original question was about replacement for NJM2068 - pretty old dual amp. Bias current runs here 150nA typ. and 1000nA max (it doesn't get much worse than that) - LM4562 is good candidate here.

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!