The circuit idea I have explained below enables a power amplifier loudspeakers to switch ON only when there's an input music available, otherwise it makes sure that the loudspeakers remain shut off. The idea ws requested by Mr. David Alda.
Technical Specifications
Your site is just awesome.
I'm hoping you can post a tweak to your post of 10-1-2013 entitled:
Sound Activated Automatic Amplifier Mute Circuit
I need the opposite of that circuit. What I need can be used in recording studios, broadcast studios, etc.
When the input is very low (or none), the output of the amp will be muted. When there is input sound, the amp will function un-muted. The amp needs to have enough power to power a computer type speaker at moderate to high volume levels.
As it will be used in real life:
When computer recording software (or a PC sound card) is not sending out any sound, the circuit will clamp the output so that zero noise is heard in the speaker in the studio. But when the recording software is sending out an input signal, the amp will function normally and drive the studio speaker at an adequate volume level.
On behalf of all those you have helped, thank you. May you be blessed in every way.
Is there any audio I can voice for you for free?
David Alda
Voice over talent & audiobook narrator
The Design
The requested circuit for implementing a music activated amplifier speaker can be witnessed in the figure above.
The idea looks pretty simple but consists of crucial stages which cannot be replaced by any other form of circuit stages.
The music feed (extracted from the power amp input) is applied to the input of an LM386 mini amplifier circuit set at a gain of 200, which is maximum gain for this IC.
The hi gain setting allows the amplifier to sense even the minutest level of input signals, although this may be set as per the users preference through the given input volume control pot.
Using LM386 as Music Amplifier
In the presence of a music input, the LM386 amplifies it to the required levels and the output is acquired at the output pin#8 of the IC through an AC coupling 250uF capacitor, and applied across an condenser inductor which should be preferably a "buzzer coil". You can see the image of a buzzer coil below:
Function of Buzzer Coil
The buzzer coil makes sure that the amplified music is further boosted to higher levels in order to make it compatible with an opto coupler input LED.
The optocoupler 4n35 can be seen connected across the coil, the built in LED inside the opto responds to this music voltage and lights up which in turn switches ON the internal photo transistor of the opto.
The emitter of the photo transistor inside the opto now begins conducting so that the connected external relay driver transistor BC547 receives enough base drive to activate the relay.
The relay switches ON immediately in response to the above procedures and connects the power amplifier's output with the loudspeakers.
Conversely, in an absence of a music signal or insufficient music at the input, the LM386 and the output coil are unable to sustain any voltage at the output, which keep the opto and the relay driver stages switched OFF, the loudspeakers also stay off because of this, until a legit music input is sensed.
The 100uF capacitor at the base of the BC547 transistor makes sure that the relay does not chatter in case the input carries a fluctuating or intermittent music signal.
Questions & Answers
Music Triggered Amplifier speaker. I am actually looking for something that can turn off the amplifier power in case there is no music played with in 5 minutes (Variable) after turning on the amp. This way we can build a kind of eco mode on to the amp. The amp will continue to be on as long as there is a input signal with any one of the pre outputs. A similar one on the preamp will also help.These days most higher end brands incorporate an eco mode for power saving
You can try the following circuit, but it will not give 5 minute delay, it will give not more than 30 second delay switch OFF
can I use this (Music Triggered Amplifier Speaker Circuit) to switch on LEDs instead of speakers, does the music input need to come from amp or line out/headphone thank you,
yes, you can use any type of load with the relay instead of the speaker.
amplified input is not required since the LM386 is itself an amplifier and is incorporated for amplifying even small signals at the input
sir can I use +vcc and -vcc here and if yes how would I do that?
Jindro, you can use a normal +/- single supply across the lines which are connected with pin#6 and pin#4 of the IC LM386
tnk u for the reply Sir! I’m a newbie in audio amp making and someone say that it will be better if I have a dual powerful for an audio amp, but I’ve only seen a + and grnd on power input. how would I connect +vcc, -vcc, and GND in it Sir?
Jindro, you can use dual supply for your power amplifier unit, for the above shown LM386 music detector circuit dual supply is not required…..