This capacitor is in the negative feedback network.
At high frequencies, the amplifier gain is the ratio of the two resistors, R637/R611 + 1.
At low frequencies, the gain reduces due to the capacitor, until it approaches 0dB (x1) at DC.
This is a common approach in power amplifiers to avoid large output DC voltage offset.
It would be best to leave the capacitance value as it is.
At high frequencies, the amplifier gain is the ratio of the two resistors, R637/R611 + 1.
At low frequencies, the gain reduces due to the capacitor, until it approaches 0dB (x1) at DC.
This is a common approach in power amplifiers to avoid large output DC voltage offset.
It would be best to leave the capacitance value as it is.
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thank you for the reply rayma
so changing the value of this cap will not do anything beneficial ?
and so are these 2 resistors and the cap used like a sort of voltage divider ?
gaz
so changing the value of this cap will not do anything beneficial ?
and so are these 2 resistors and the cap used like a sort of voltage divider ?
gaz
It's a capacitor that is part of the feedback network. It reduces the DC gain to unity to limit the DC offset at the amplifier output. It also gives some low-frequency roll-off below a frequency of 1/(2 pi R611 (C605 + C607)) ~= 3.3862 Hz (assuming C607's value is in uF, which I'm sure it is). You can shift that corner frequency by changing C607 if you like. If C607 is a tantalum capacitor, changing it into an aluminium electrolytic capacitor (preferably a bipolar one) may slightly reduce distortion.
Edit: I see rayma was quicker in replying.
Edit: I see rayma was quicker in replying.
thanks MarcelvdG
i believe it is an aluminium cap, and i think i'll just replace it with the same value.
many thanks
gaz
i believe it is an aluminium cap, and i think i'll just replace it with the same value.
many thanks
gaz
R637, R611 and C605+C607 are indeed a voltage divider. The gain of the amplifier is ideally (if the open-loop gain were infinite) equal to the attenuation of the feedback divider. So when the feedback voltage divider attenuates 22.3 times, the amplifier amplifies almost 22.3 times (almost, because the open-loop gain is never really infinite).
thanks for cluing me up. i thought i had seen that configuration somewhere before.
how did you arrive at 22.3 times ?
how did you arrive at 22.3 times ?
It's the reciprocal of R611/(R637 + R611) rounded to three digits. I don't like rounding numbers, but it was just an example anyway.
By the way, there is also a voltage divider R601, C601, R603, C603 at the input that reduces the gain a bit, I didn't take that into account.
By the way, there is also a voltage divider R601, C601, R603, C603 at the input that reduces the gain a bit, I didn't take that into account.
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