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Power amplifier for DC motor?

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radagast

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Hi.

I want to build an amplifier that will have a microphone (low voltage, low current) as an input, and a dc motor at the output (it is about 60 ohm). Seeing as I'd need at the output both high voltage and high current I need an power amplifier, right? I saw that a possible design is an operational amplifier followed by a B stage. Is that sufficient, or are there other preferred designs (possibly only with bjts...) for a power amp?

Thanks.
 

sky_123

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Go to the URL here and search for the words "CLAP SWITCH".
There is a circuit there that will trigger an LED for 15 secs on sound. Replace the LED and associated resistor with a 6V relay that will
switch on your motor.
 

SunnySkyguy

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I like the Electronic resource book sky_123 for ease of reference.
I'm not sure what radagast had in mind for biasing the mic DC voltage and what voltage the motors are rated for.
6V may work if that is what he has intended. with 4 AA cells.

THere are two possibilities.
VOX toggle switch with constant Voltage (CV)
or Voice controlled torque. More elaborate voltage gain and noise filtering.
or Voice controlled one shot. THis mean it moves after a noise is detected for a short time.

The problem may occur that the motors cause more noise than the voice, then a filter is needed with mic isolation from chassis as a spring antenna.

I have no idea on his specs, really,
Do make a list of requirements.
 

radagast

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Thanks

But I don't want a switching amplifier, I rather need a linear one. ie, the motor will get more voltage and spin faster for higher input volumes. So I can't use the X seconds up circuits...

I know that a power amplifier is what I need, I'm just wondering how to design it. One thing I saw as a voltage amplifier with an opamp followed by a class B / AB to get more current...
 

sky_123

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That site has many popular circuits, now that you've specified you want the speed to vary, search for "dancing flower with speed control"..
 

SunnySkyguy

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Given that sound may range say 30 to 60dB depending on noise floor.
What range of speed control do you want?
and is that linear or log control of voice controlled speed
and modulation bandwidth is shaped, raw or LPF'd sustained, quasi peaked or peak and decay
 

rohitkhanna

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A simpler approach would be to feed your mic input to a basic pre-amp, and the use the output of this pre-amp to modulate the duty-cycle of a PWM generator which then drives a MOSFET to which is connected your DC motor.

This design will -
(1) be simpler to tune/ setup
(2) less complex
(3) run cooler than a B-amp
(4) more robust against failures
(5) ....uhh
 

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