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Old 2nd April 2015, 05:08 AM   #1
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Default Discrete class D amplifier outputs low volume

Hello everyone,
I have a discrete class D project that I need help with but since I'm not an analog guy I got a problem. So far I got everything set up and the discrete class D works perfectly. But it outputs a low volume sound due to the DC voltage which is about 6 volts, if I increase the voltage I'll burn my circuit. So How do I increase the volume of the speaker so my circuit can handle up to 35V to get a high volume sound.

on the attachment is the schematic and simulation.

I'd appreciate tips and help.
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File Type: jpg Simulation.JPG (267.6 KB, 123 views)
File Type: jpg ClassD circuit.JPG (120.8 KB, 128 views)
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Old 2nd April 2015, 10:08 AM   #2
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where is the feedback?
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Old 2nd April 2015, 10:31 AM   #3
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Quote:
Originally Posted by ionutzxpo View Post
where is the feedback?
I dont have a feedback, why I need it? And feeding back from where? Sorry I'm not expierened with analog circuits.
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Old 2nd April 2015, 10:46 AM   #4
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Quote:
Originally Posted by ionutzxpo View Post
where is the feedback?
I don't have a feedback, why do I need it? I'm sorry I'm not experienced with analog circuits.
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Old 2nd April 2015, 01:31 PM   #5
wwenze is offline wwenze  Singapore
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Emitter resistor of Q1, it's missing.
Edit: Ok I see the shunt feedback via R2. But you still need the emitter resistor because it adds a way to control your DC point. Right now your purple waveform is stuck at -5.5V plus VBE of Q1.

Also your DC levels are all over the place. Pink and yellow (and/or purple, depending on how you do it) should have the same DC level.

Get the green waveform working first, then you can look at adding a post-filter feedback later too.

Also, try simulating with 0V input and audio frequency input first.

Last edited by wwenze; 2nd April 2015 at 01:56 PM.
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