Is there such a thing as a standard for output line level impedance? What would be considered as "normal" line level output impedance? Does anybody know the line level input impedance on Magnavox bi-amps? On the regular Magnavox amps such as the 88 series or on the 93 series? I have been lamenting since time immemorial of the strangled bass response on the bi-amps I own. I have had some tinkering time in the shop the last couple of days and have perhaps discovered that I may be slandering devices that are not totally at fault. It seems like every device I connect to the tape input on the Concert Grand gives a different bass response. The reel-to-reel deck somewhat the best bass response, the RCA CD changer, somewhat the most pitiful bass response. I don't have a working record changer in either of my big Magnavoxes, but FM doesn't sound all that bad. FM around here is mostly commercials and Spanish music, mixed in with some rock. I realize most FM stations mix their audio so it will "boom" when people drive around town with their trunk full of subwoofers. But it at least lets me get the hint that the CG is capable of reproducing decent bass. This got me to thinking that maybe part of the problem is what I have been feeding it, what I have been using to reproduce music. Since a Concert Grand was built as a big record player with the radio tuner and inputs as an afterthought, I decided maybe a little experimentation was appropriate. Would a graphic equalizer between the input device and the amp provide a better impedance match? Or would it overdrive the amp? I don't have one of those devices everybody uses, whose name has escaped me. Bluehound or Blueberry, something like that. Bluetooth, that's it. Bluetooth. Would a Bluetooth sound better/different than the old fashioned devices I'm using? There has got to be a design change between the bi-amps and the regular amps that cause strangled bass in the tape input. I have looked at and studied schematics, but I don't see a difference. The tuners used with bi-amps have a cathode follower circuit, but I don't know how that would change the input impedance. Any thoughts or ideas?
Another thing I'll mention in passing. Years ago, there was a discussion on ARF about this very topic. A member there whose is a retired electronics engineer and who gives considered and accurate opinions, suggested inserting a 3300 ohm resistor in the input of bi-amps to change the crossover frequency between the treble amp and the bass amp. I haven't done that, but that does suggest that perhaps output/input impedance is a factor.
