ABSTRACT
The vast majority of audio circuitry runs from dual supply rails; this has been the case ever since opamps became common in audio in the 1970s, and it was established that electrolytic capacitors could work satisfactorily and reliably without DC bias on them. Some opamps clip earlier in one direction than the other, and a slight adjustment up or down of the half-rail may allow a larger symmetrical output swing. One of the great advantages of dual-rail operation is that the opamp supply currents, which to some extent have the same half-wave rectified nature as those in a Class-B power amplifier, are inherently kept out of the signal ground. The AD8397 is another promising possibility, because it claims a very voltage-efficient output stage and good load-driving capabilities. The input noise density is somewhat higher at 4.5 nV/Hz , slightly better than a 5532 and slightly worse than a 5534.
