I have stated so too.
I gave my reasons why it should be so.
So far those that suggested otherwise have not come back to explian why my reasons are wrong.
What is your reasoning for this conclusion?
No, the Zobel in the LM1875 schematic is to remove the inductive appearance of the amplifier's output (caused by loss of NFB at high frequencies due to gain bandwidth).
That's why it needs to be right on the output - so it comes before any stray capacitance coupling to the output wiring.
It is not intended to compensate for the output coil -- the "auxiliary amplifier" diagram in the LM4780 datasheet shows the output inductor, and the Zobel is placed before it.
A separate Zobel will need to be applied to the loudspeaker to compensate for the driver inductance. A Zobel correctly designed to perform one of these functions will not perform the other effectively.
Thanks for the explanation. The way I understood it was that the amplifier would be looking at the inductance of the voice coil and the inductance of the output coil in series with each other, and the Zobel needed to be closer to the chip (before the output inductor) in order to be able to compensate for both those effects. Should have thought of the gain droop at high frequencies as well.
So if there were two Zobels without an output inductor or a crossover inductor, would the amplifier not be looking at a lower than expected output impedance at high frequencies? Or does the GBW (or indeed the inductance of the speaker wire itself) take care of that by itself ? Or, as I understand it, the second Zobel is required only if there is more series inductance - either with an output coil or one in the crossover...
So if there were two Zobels without an output inductor or a crossover inductor, would the amplifier not be looking at a lower than expected output impedance at high frequencies? Or does the GBW (or indeed the inductance of the speaker wire itself) take care of that by itself ? Or, as I understand it, the second Zobel is required only if there is more series inductance - either with an output coil or one in the crossover...
I have built a pair of LM1875 amplifiers (as per the typical application) on stripboard and they seem to be working fine. I put the reccomended Zobel right on the output of the chip.
This is required as well as the on-board Zobel to ensure stability? How would you reccomend I approach this? I could put it inside the speaker cabinet, or on the amplifier output terminals if it is generic enough to be applicable to most applications (though this should only be used with the speakers I posted the plot for earlier). Any suggestions on component values?
This is required as well as the on-board Zobel to ensure stability? How would you reccomend I approach this? I could put it inside the speaker cabinet, or on the amplifier output terminals if it is generic enough to be applicable to most applications (though this should only be used with the speakers I posted the plot for earlier). Any suggestions on component values?
Hi,
the amplifier Zobel is an amplifier stability component. It belongs with the amplifier.
The speaker Zobel is a reactance correction for the speaker. It belongs with the speaker.
These two R+C have the same name but their purpose is completely different.
You must not move them from their respective optimum locations.
the amplifier Zobel is an amplifier stability component. It belongs with the amplifier.
The speaker Zobel is a reactance correction for the speaker. It belongs with the speaker.
These two R+C have the same name but their purpose is completely different.
You must not move them from their respective optimum locations.
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