Author Topic: Complete 300 watt audio amplifier project  (Read 717 times)

Offline profdc9

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Complete 300 watt audio amplifier project
« on: November 13, 2020, 01:17:41 PM »
Hello,

I have designed and made available schematics, gerbers, heatsink drill patterns, and construction documentation for a 300 watt class AB BJT-based audio amplifier.   It is intended to be a complete design for educational study that also has flexible part substitution.  It can be found at the github

http://www.github.com/profdc9/PowerAmpAudio

It is a high quality amplifier you can build yourself, save some money over an expensive commercial amp, and learn how to do it in the process.   It includes the amplifier, a power conditioning PCB, a soft start PCB to limit current inrush, and an balanced (XLR) to unbalanced input.

Check out the github, there's a lot of stuff there.

Offline klugesmith

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Re: Complete 300 watt audio amplifier project
« Reply #1 on: November 13, 2020, 11:57:45 PM »
Thanks for sharing, and motivation to dust off Github registration here.

Reminds me of a basic audio amplifier kit from 1970's, Universal Tiger by Southwest Technical Products. Mine probably need new capacitors.  Occasionally discussed in the past decade at DIY Audio forum.

Here's a question that's more easily asked on a forum than answered by measuring.
How do amplifiers like these handle frequencies much above 20 kHz?
Would they be practical for driving 30 kHz or 60 kHz sine waves at 100 watts?
Into an 8 ohm resistive load, or an ultrasonic transducer, or a ferrite-cored high voltage transformer? 

Offline profdc9

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Re: Complete 300 watt audio amplifier project
« Reply #2 on: November 15, 2020, 03:11:16 AM »
Generally they will drive frequencies up to about 100 kHz into 8 ohms with increased distortion.  The amplifier uses the high open loop gain to minimize distortion and this is reduced at higher frequencies.  Capacitive loads can definitely destabilize the feedback, and many ultrasonic devices are capacitive.  Some combination of resistance/inductance network is usually used to limit the current through capacitive loads.  Inductive loads are less of a problem but of course high inductance means that the effective load impedance is increased at high frequencies (and current is less).

With the ON Semi transistors with 30 MHz fT and good SOA (MJL1302/MJL3281), you can drive hundreds of watts using 4 NPN/PNP pairs so 100 watts should be no problem.

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Re: Complete 300 watt audio amplifier project
« Reply #2 on: November 15, 2020, 03:11:16 AM »

 


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