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I have got a probably very dumb question. I was not able to find an answer on the other topics because they always described the use of transistor as a switch for other applications.

I have a circuit with audio signal passing through and going to a speaker. I would like this signal to be grounded unless a 5V TTL signal is on. In this case this will have to go to the speaker. Can I do it with a transistor?

All the example that I found are about something (like a LED) already connected to a a voltage and then with the transistor either grounding its cathode or not and I do not know whether this would work in the other direction (what I would like to do).

Can I use a transitor to ground/mute the audio signal when TTL signal is zero?

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    \$\begingroup\$ Speaker signal is usually AC and must not have any significant DC offset. Sounds to me like a job for a relay. \$\endgroup\$
    – Turbo J
    Jul 16, 2018 at 15:51
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    \$\begingroup\$ what kind of powers are we talking here? You usually wouldn't want to ground your speaker-driving output, because that means converting all amplifier output power to heat in your transistor. \$\endgroup\$ Jul 16, 2018 at 15:51
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    \$\begingroup\$ ie. are you positively sure you want to ground your output and not just disconnect it? What's the bigger thing you want to build here? \$\endgroup\$ Jul 16, 2018 at 15:52
  • \$\begingroup\$ What you want is an audio Mute control input. But what Amplifier? \$\endgroup\$ Jul 16, 2018 at 16:28
  • \$\begingroup\$ @MarcusMüller, the OP is asking about using a transistor to ground the audio input (in the title at least .... the rest of it is unclear) \$\endgroup\$
    – jsotola
    Jul 16, 2018 at 16:48

2 Answers 2

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If what you want is the ability to switch between audio and silence, you can use an analog mux to switch between your audio input and ground, instead of the amplifier output. As an example, you would ground S1, S2, and A1, hook up your low power audio source to A0, connect A to your amplifier, and use S0 as your switch input.

If you want stereo, you'll need to use a chip that has two analog multiplexers, and repeat for each line.

enter image description here

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  • \$\begingroup\$ yes this could work but I do not have access to the low power audio source but just the signal getting from the amplifier \$\endgroup\$
    – MNP_88
    Jul 16, 2018 at 19:12
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I have a circuit with audio signal passing through and going to a speaker. I would like this signal to be grounded unless a 5V TTL signal is on. In this case this will have to go to the speaker. Can I do it with a transistor?

The easiest cheapest option is to use a 5 volt electromagnetic relay. It has a switch contact operated magnetically by a coil driven electrically. Like one of these: -

enter image description here enter image description here

Pins 2 and 5 are the coil and pins 1, 3 and 4 is a changeover contact.

You might need to consider using a transistor to buffer the coil from the TTL signal because the coil current can be as high as 100 mA. Use this: -

enter image description here

Take care not to ground the amplifier output in case it gets damaged. Instead open circuit the speaker.

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  • \$\begingroup\$ great thanks! I think this is exactly what I need. And I will not ground the audio signal with the relay but just disconnect it from the speaker. Could you please tell me which kind of transistor I should use? \$\endgroup\$
    – MNP_88
    Jul 16, 2018 at 19:11
  • \$\begingroup\$ Take the tour @MNP_88 \$\endgroup\$
    – Andy aka
    Jul 16, 2018 at 20:17
  • \$\begingroup\$ you actually ought to ground the input to the amp when you want no signal, otherwise you are might get low level signals or other odd noises. \$\endgroup\$
    – danmcb
    Jul 16, 2018 at 21:59

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