EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: skrph on December 02, 2021, 04:27:08 am
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Hello everyone! First post on the forum here, excuse any bad etiquette I may have :)
My class's end-of-semester project is to build something involving opamps. I've decided to build a theremin, and I've been plotting it out on ltspice. I used an opamp (U2) to prevent the speaker from pulling any significant current from the frequency generator, but even then, there's only about 0.3 volts going across the speaker. I'm assuming that the speaker has 4 ohms of resistance and 0.2mH, after some brief googling on the average speaker. Attached is the .asc file.
(https://i.imgur.com/4aEiWX8.png)
How would I get more power going through the speaker so I could actually hear the tone that's being produced?
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Add an audio amplifier to the output of your circuit.
Something like LM388 would do the job.
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Check the datasheet, the short-circuit current is about 30mA at best...
The OP07 is a signal amplifier, can't drive heavy loads, you need a power stage.
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For the sake of me learning from this as well:
-Why no capacitive coupling?
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Use another made for purpose of amp as actual amplifier, or grab a TDA2030 5 pin amp chip
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Op amps tend to operate around the half way point between the positive and negative supplies (note the dual power supply). This is true of both the input and output sides of the op amps. So, if they are properly biased to operate at that point, capacitive coupling is often just not needed.
Tube and discrete transistor audio circuits often need to be biased with a single supply and the DC level of the output of one stage can easily be high enough to drive the following stage into either cutoff or saturation if it is directly coupled to a tube's grid or transistor's base. So, coupling capacitors are often used to allow the output circuit to work at it's desired operating point while the input circuit of the following stage can also operate where it works best - or just plain where it works in the first place.
For the sake of me learning from this as well:
-Why no capacitive coupling?