I did not say nothing is reproduced or usable below 70hz. I did say according to Sharps own specifications, they rate the bass amps starting at 70hz which suggests that it is not nearly optmized for 40hz, which is what YOU said. In fact, I made it clear that it was not a hard cut off, but rather a progressive roll off. If this system was strong at 40hz, Sharp (and any other manufacturer) would certainly advertise it.
As for 90w pmp (which is marketing hype) -- if you want to go with that and not RMS, then go right ahead. Might as well call it 300 watts super-pmp instead.
As for the specifications, I copied those directly from my factory original service manuals (I have 2 copies). I'm not motivated to go through the trouble of posting those here for you. You can believe it or not. There are pdf copies floating around. But it most definitely is 10% THD, a ratings point which virtualy all boomboxes use. You said yourself that you presumed 1% which you said is the standard rate used for amplifiers. Again, don't know where you got that impression from. There is no standardized THD point in which to rate amplifiers. Most home audio amps aren't even rated at anything above .25% or so.
As for the first diagram you showed, it is not a schematic. It is a block diagram which merely shows the intended circuit layout. It offers NO real circuitry. Think of a block diagram as representation of a circuit with blocks connected by lines showing the principle functions of each circuit and it's relationship with each other. They help to better understand how a circuit was designed. They do not generally include any details of the actual circuitry.
As for the second diagram, that is in fact a schematic. Unfortunately, you are reading it completely wrong. First, the preamp circuit isn't even on that diagram, it's on another diagram. What you are seeing is the power amplifier circuit. The HA1392 chips you see are the actual output chips. There are 2 chips, each with dual amps. The headphone circuit you speak of is in series with the full range speakers and is not a preamp'd signal but rather full power circuits. When you plug in the headphones, it cuts out the speakers.... and feeds the headphones instead.... try it and see. You are correct in saying that the bass amp input signal is tapped to the headphones. IF YOU READ MY POST CAREFULLY, I said that the bass amp gets it's input from the full range amplified signal. You just don't know it because you are interpreting the amps wrong. At this point, let me educate you something..... The amplfied signal is too high to be fed directly to the bass amp. So it is attenuated via R817 and R818. Pins 2 & 5 of the HA1392 are the L/R inputs. Remember what I said? The amplfied signal is attenuated, then reamplifed. Now, at this point, the signal is further attenuated by VR801 and 802. Those are your superwoofer controls behind the grills. Finally, on each leg of the inputs, there is a simple RC circuit (filter). Remember how capacitors work? They pass high frequencies and block low frequencies depending on it's value. Check out the opposite leg of that parallel RC circuit.... IT GOES TO GROUND! So again, like I said, highs are shunted to ground retaining the low frequencies to feed the bass amp. The capacitor and resistor is exactly the components referred to in the block diagram as "LPF". Now in order to have an active filter, you need active components. This would be an opamp or a transistor. NOTICE how there is NO active components in that filter unless you count the main full range amplifier, only the passive resistor and capacitor is what comprises the bass filter. Taking the bass amp input signal from the preamp would've involved additional smaller amps mentioned above, which would've increased cost and complexity. This is why the signal was instead taken from already amplified end of main amp and then attenuated, recycled, filtered and fed to the bass amp. This is again, not a good way of doing it but given that subwoofers generally produce little intelligible audio anyhow, high distortion is not as concerning. A rumble and distorted rumble might not sound that much different. Most GF-777 owners will notice that the center bass amps do sound quite distorted at higher operating levels. Again, taking a distorted signal and amplifying it, multiplies the distortion, especially when the distortion of the bass amp itself is added to the distorted input.
Anyhow, I enjoy a spirited geek conversation as much as anyone, but I've said all I am going to say here and won't waste anymore of my time debunking your theories. If you want to say your boombox sounds great, then that is fine and I have no problem with that, in fact, I'd tend to agree. If you want to say I'm wrong in my interpretation of specifications that is right in front of me, or that I'm reading a circuit wrong, then that's different story. Consider what I said and maybe learn something, or not. Up to you.
As for 90w pmp (which is marketing hype) -- if you want to go with that and not RMS, then go right ahead. Might as well call it 300 watts super-pmp instead.
As for the specifications, I copied those directly from my factory original service manuals (I have 2 copies). I'm not motivated to go through the trouble of posting those here for you. You can believe it or not. There are pdf copies floating around. But it most definitely is 10% THD, a ratings point which virtualy all boomboxes use. You said yourself that you presumed 1% which you said is the standard rate used for amplifiers. Again, don't know where you got that impression from. There is no standardized THD point in which to rate amplifiers. Most home audio amps aren't even rated at anything above .25% or so.
As for the first diagram you showed, it is not a schematic. It is a block diagram which merely shows the intended circuit layout. It offers NO real circuitry. Think of a block diagram as representation of a circuit with blocks connected by lines showing the principle functions of each circuit and it's relationship with each other. They help to better understand how a circuit was designed. They do not generally include any details of the actual circuitry.
As for the second diagram, that is in fact a schematic. Unfortunately, you are reading it completely wrong. First, the preamp circuit isn't even on that diagram, it's on another diagram. What you are seeing is the power amplifier circuit. The HA1392 chips you see are the actual output chips. There are 2 chips, each with dual amps. The headphone circuit you speak of is in series with the full range speakers and is not a preamp'd signal but rather full power circuits. When you plug in the headphones, it cuts out the speakers.... and feeds the headphones instead.... try it and see. You are correct in saying that the bass amp input signal is tapped to the headphones. IF YOU READ MY POST CAREFULLY, I said that the bass amp gets it's input from the full range amplified signal. You just don't know it because you are interpreting the amps wrong. At this point, let me educate you something..... The amplfied signal is too high to be fed directly to the bass amp. So it is attenuated via R817 and R818. Pins 2 & 5 of the HA1392 are the L/R inputs. Remember what I said? The amplfied signal is attenuated, then reamplifed. Now, at this point, the signal is further attenuated by VR801 and 802. Those are your superwoofer controls behind the grills. Finally, on each leg of the inputs, there is a simple RC circuit (filter). Remember how capacitors work? They pass high frequencies and block low frequencies depending on it's value. Check out the opposite leg of that parallel RC circuit.... IT GOES TO GROUND! So again, like I said, highs are shunted to ground retaining the low frequencies to feed the bass amp. The capacitor and resistor is exactly the components referred to in the block diagram as "LPF". Now in order to have an active filter, you need active components. This would be an opamp or a transistor. NOTICE how there is NO active components in that filter unless you count the main full range amplifier, only the passive resistor and capacitor is what comprises the bass filter. Taking the bass amp input signal from the preamp would've involved additional smaller amps mentioned above, which would've increased cost and complexity. This is why the signal was instead taken from already amplified end of main amp and then attenuated, recycled, filtered and fed to the bass amp. This is again, not a good way of doing it but given that subwoofers generally produce little intelligible audio anyhow, high distortion is not as concerning. A rumble and distorted rumble might not sound that much different. Most GF-777 owners will notice that the center bass amps do sound quite distorted at higher operating levels. Again, taking a distorted signal and amplifying it, multiplies the distortion, especially when the distortion of the bass amp itself is added to the distorted input.
Anyhow, I enjoy a spirited geek conversation as much as anyone, but I've said all I am going to say here and won't waste anymore of my time debunking your theories. If you want to say your boombox sounds great, then that is fine and I have no problem with that, in fact, I'd tend to agree. If you want to say I'm wrong in my interpretation of specifications that is right in front of me, or that I'm reading a circuit wrong, then that's different story. Consider what I said and maybe learn something, or not. Up to you.
I am very surprised they did this & a split signal from a pre-amp would make more logical sense. I'm hoping you can understand my general assumptions as being within the realm of reality & you can't deny the signal is sloped before the amps & it's putting out LOTS of bottom end without lots of boost to the signal, even at 20HZ!!! The volume is at 3, the loudness is on & the bass at 3:00 position during the video while the superwoofer controls were flat.
