If he's able to get that much of an improvement with 5532s, I'm curious what he could get if he used modern opamps. Granted, the 5532 has been the opamp to beat

If he's able to get that much of an improvement with 5532s, I'm curious what he could get if he used modern opamps. Granted, the 5532 has been the opamp to beat for sound quality for decades, but someone posting by the handle NwAvGuy dis a shootout of opamps comparing and measuring the specs that actually matter for quality audio use back in 2011[1]. That was 7 years ago, and the various component vendors have released some new devices since. I suspect a slight redesign using a 2068 for the gain stage and a 4556 for the buffers would do even better, and drain the batteries slower because of less quiescent current of modern devices. The circuit design looks weird to me. Wouldn't it be better to use a inverting setup on the opamp to get get some attenuation, and then feed the gain stages into a high-current opamp like the 4556 as a buffer to drive the headphones, or perhaps a transistor that'd be good at the job? And why are there a pair of parallel gain stages on the ground line? Why not just throw your gain stages on the signal lines, ground ground and let it be ground? 1. https://nwavguy.blogspot.com/2011/08/op-amp-measurements.html https://nwavguy.blogspot.com/2011/08/op-amp-measurements.htm...