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I'm normally a software guy, so please bear with me :-)

I have a TDA2030A amplifier board like this one that I'm using to play audio through a small speaker. I have a microcontroller which I want to use to switch on/off the amplifier.

For my first attempt, I put a MOSFET in series with the amplifier's power line. But the speaker produces an audible pop when the MOSFET switches off, which I believe is happening because the speaker is biased around 12V (the amp is powered from 0V & 24V, not ±12V), causing the speaker cone to suddenly jump from its 12V "zero point" when power is disconnected.

I've seen people recommend a relay in series with the speaker that is to be switched off before the amp is switched off. That makes sense for a 0V-biased audio signal, but it got me wondering: Can I use a MOSFET instead of a relay? It seems to me like this should be a viable solution because the audio signal never goes below 0V, so the voltage would never reverse directions across the MOSFET. Would this work?

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  • \$\begingroup\$ I'd say draw a schematic diagram with the amplifier, FET and speaker how you would connect them. Then we can say if it works or not. PFET or NFET, connected where and which way? The speaker can't have a positive voltage over it as they damage with DC, so please be sure what point in the circuit you think is always positive. \$\endgroup\$
    – Justme
    Oct 23, 2023 at 17:20
  • \$\begingroup\$ @CarmenCarmen Edit the question, there is a tool to draw circuits. \$\endgroup\$
    – Voltage Spike
    Oct 23, 2023 at 18:37
  • \$\begingroup\$ get another module; many other cheap one have power switches/pin that you just need to pull down to put to sleep. \$\endgroup\$
    – dandavis
    Oct 24, 2023 at 1:01

2 Answers 2

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It's inadvisable to put 24V on an amp specified to work with 6V–12V. Assuming the amp is biased at voltage halfpoint and you use +12V (say), the output before the big capacitor will swing around 6V. The output after it is AC; symmetric around 0V. If you want to put a MOSFET to work and find one with a turn-off voltage that leaves you enough headroom for both on and off state, you need to place it before the output capacitor. And if you switch the MOSFET on/off during active play, you may end up using the capacitor as a charge pump, putting double the maximum voltage through the speaker when switching it back on, with the resulting peak current possibly making both the speaker as well as the TDA2030A unhappy.

It may be smoother to use a JFET for shorting the unamplified signal conditionally.

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The amp board is advertised to work with 6 to 12 VDC. The heatsink looks minimal, so think a while; could it really stand the 300% higher dissipation caused by 24 VDC supply and the higher output levels which become possible with the higher supply voltage. The electrolytic capacitors as well can be underrated for 24 V operation.

One of the capacitors is probably in series with the speaker to make single supply operation possible. It passes only AC current to the speaker. Making a MOSFET switch for the AC current is substantially tougher task than inserting a MOSFET. As an additional board it's more complex than the original amp board.

My suggestion: Build a circuit which uses a relay to disconnect the speaker during the turn on and turn off transitions of the amp. Let there be in the place of the speaker a resistor, say 100 to 200 ohms which allows the series capacitor in the amp output to get charged before the speaker is turned ON. The resistor causes no harm when it's in parallel with the speaker.

An alternative: Mute only the input signal of the amp. Such circuit can be designed for ex. with an LDR or a voltage controlled amp IC to be so smooth that no audible clicks occur. I would try the LDR approach.

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