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   to get maximum output swing thus power
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   to get maximum output swing thus power
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3. To compensate for inevitable series resistors at the TPA6120 outputs,
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3. To compensate for inevitable series resistors at the TPA6120 outputs,
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   use opamps.
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   use opamps.
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4. Output resistors should be of high thermal power, preferably MELF
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4. Output resistors should be of high thermal power, preferably MELF or 1205
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(general)
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(general)
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1. Use metal film feedback resistors (bigger than 0805, best if MELF),
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1. Use metal film feedback resistors (bigger than 0805, best if MELF),
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(low-pass filtering)
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(low-pass filtering)
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3-rd order butterworth, 30kHz -3dB.
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3-rd order butterworth, 30kHz -3dB.
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First stage for AY is 2nd order Q=1, (multiple-feedback). 1st stage is 2nd order to keep input impedance more or less constant for AY/YM.
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First stage for AY and for BEEP is 2nd order Q=1, (multiple-feedback),
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For beeper there's low impedance buffer, we use single 3rd-order opamp based stage.
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Second stage is just 1st-order RC
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Second stage is just 1st-order RC
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Some extra filtering for BEEP at higher freq.
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(high-pass filtering)
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(high-pass filtering)
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distributed (?) "synchronous" (or not so) 1st-order high-pass filters with electrolytics.
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"distributed" 2nd-order high-pass filters with electrolytics.
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<<20Hz cutoffs
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<<20Hz cutoffs
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(line output vs. headphones output)
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for headphones there's a need for huge output capacitor.
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For line output relaxation time would be then too big (like tens of seconds), so need different (smaller) cap.
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Also maybe have line output without volume regulation, from summing opamps.
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