> They mention it buffers with a gain factor of 0.1, but I don’t understand how the four op-amps play together to eliminate the hiss. I'm not entirely sure, bu

> They mention it buffers with a gain factor of 0.1, but I don’t understand how the four op-amps play together to eliminate the hiss. I'm not entirely sure, but it appears that this is setup to amplify the ground noise. I'm also not entirely sure why you would want a gain of 0.1, you would probably want to preserve as much amplitude information as possible. Also the power circuit on the left shows a resistor ladder with 9V over a 1k resistor on one side, and the same for the other. 9 / 1000 = 9mA, x2 is 18mA. Added with the amplification of noise, I can see where 25mA may come from. > Yeah, and two op-amps for the ground filter has me stymied as well. I think this is because it's the ground for both the left and right channels, which is potentially two op-amps worth of power and you don't want this dumped through the headphone jack. I haven't tested this, but would probably go for a simpler design like this: https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWEB2WZIICxgEwGZMA2QgDmRMJAUiqpoQFMBaMMAKAEMQdISQSaeHvxoBOEOKbj08OCCZ5oosHjyiSohKOSjMmPEgVKV+gaLzlMkVeFmRO3XtwSUhNHC4leptu-JzQhMi4OB4I5JDmfEwBQbiYojjIcASafDLwbABOjul6IG7g+TSYydm5BcKFhSVlAO6VglXCHpT2DYVg+YUCUGwNPHyilINFmH0DTkk4FTVsAF6zpI0FyzMAJgwAZhwArgA2AC5M8wwAdgxZbABK4MiUYIlj4E80JW9QnzAI5WD3IIRxn8Hq9fHBfv9HjNgdwrJ8Mu07iM4aMcHDEaNAUiAeN7H8aGAHjhooTwMTuI5HPQoNB0D98eARp4WEyRpSeNSYOwGaSofJeU9ofQ3rSaewcjCsawZliCZkJf80QTcLCPhk2AAPfmQZDgAjyQjSCwgcZokD7baHTUFOEmArkPW603jC1bK1aljobjLJhYbjBE2wkBZACWAHMABbu7XpbQGvBUwNmsNndb9RkvGbDTMTCQgrOUKxvdPZosVMuImF8gzQ17pms5ht4ZaIpvLaot9PS1XgFWtXPd-u9fuI3q4dIq8cDyfk7uytgAeRWvSI4zHfSXDb5q5zEHsm5anh3-b3bAAzhmp2PyR8dvszwxzxmh+5PLeOPfH4t+2XRr+QJsOwHMcpwXFcOSFL+R5yHK4KTHwzZ8H+MH1lU7bCBWbAAPY2jinxWOoNKyPcODmLoCB4LgSBcvC2EFAmsompEfDUaKEDsDhBh4e8hGsRA0JsEAA https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB...