Agreed, with the addition that C4, R9 come into play at around 140kHz. So while it rolls off the loop gain for stability it has no influence on the audio bandwidth.
(He calls it R1, C1 in the text, which is different from the figure).
It's a bog-standard circuit you could have found in a data sheet.
Jan
(He calls it R1, C1 in the text, which is different from the figure).
It's a bog-standard circuit you could have found in a data sheet.
Jan
R4 sets the overall gain; consider the opamp and chipamp as one amplifier, it will be clear then.
C3 compensates the loop for the opamp, until a frequency where the C3 inpedance is equal to R3. Then it flattens out, until the impedance of C12 becomes equal to R3, then the roll of continues. It's called a shelving equalizer.
This all happens at high frequencies, no impact on the audio, just to keep the loop stable. There's a lot of gain and phase shift from two amplifiers so you need to manage all that carefully.
Jan
C3 compensates the loop for the opamp, until a frequency where the C3 inpedance is equal to R3. Then it flattens out, until the impedance of C12 becomes equal to R3, then the roll of continues. It's called a shelving equalizer.
This all happens at high frequencies, no impact on the audio, just to keep the loop stable. There's a lot of gain and phase shift from two amplifiers so you need to manage all that carefully.
Jan
As you know, you can decrease distortion by increasing the feedback. But to do that, you need to increase the open loop gain, because the feedback is the difference between the open loop gain and the closed loop gain, and the closed loop gain is fixed, around 25 for an audio amp.
To increase the open loop gain you can put two amplifiers in cascade, as is done here. So now you have an open loop gain which is the product of the two open loop gains of the NE5532 and the TDA2030. But you're not done yet.
The chipamp needs at least a gain of 20 for stability. That is done with R8 and R7. Then R4 with the two input resistors R1 and R2 sets the overall gain.
And, because putting two amps in cascade not only increases the gain, it also increases the phase shift in the loop, hence the fancy compensation.
Straightforward, really
Quizz: what is the midband gain from input to output of the NE5534?
Jan
To increase the open loop gain you can put two amplifiers in cascade, as is done here. So now you have an open loop gain which is the product of the two open loop gains of the NE5532 and the TDA2030. But you're not done yet.
The chipamp needs at least a gain of 20 for stability. That is done with R8 and R7. Then R4 with the two input resistors R1 and R2 sets the overall gain.
And, because putting two amps in cascade not only increases the gain, it also increases the phase shift in the loop, hence the fancy compensation.
Straightforward, really
Quizz: what is the midband gain from input to output of the NE5534?
Jan
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