I wonder if anyone has ever taken apart their PL-660 and PL-680 to make a side by side comparison, right to the discrete components on the circuit board. Years ago I've read someone saying that the speaker for the PL-680 differs from the PL-660. I forget which has what, but one of them has a 4 Ohm speaker and the other one, 8 Ohm. I find my PL-660 is harsh sounding and trebly while the PL-680 has a smoother, bass rich audio. I'm not sure if this difference is attributed to the tone control circuit (Bass/Treble), the different speaker impedances or the radio's enclosure. Even stranger still is the fact that both my PL-660 and PL-680 have the same firmware version (6622). I presume yours have the same firmware version too.
