Author Topic: PCB's of Ampslab C300 Class AB amplifier  (Read 322 times)

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Offline profdc9

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PCB's of Ampslab C300 Class AB amplifier
« on: August 30, 2020, 08:05:22 am »
I am working on building a stereo amplifier using the C300 amplifier of Michael Chua of Ampslab.  It is a Class AB BJT-based stereo amplifier capable of 300 watts per channel.  I have the PCB's on my github at

You can read about the C300 at

There are four PCBs in the project so far:

1.  C300 amplifier PCB
2.  Power supply rectifier and filter
3.  Soft start PCB for toroidal transformer and capacitor bank
4.  Balanced XLR to unbalanced input for the amplifier

The schematics and gerbers are all there as well as BOMs with component part numbers mostly from , with a few digikey and Mouser parts as well.

We have ordered all of the stuff and are going to photodocument the build.  As an example I have a screenshot of the PCB.


The following users thanked this post: ghubbell

Offline ghubbell

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Re: PCB's of Ampslab C300 Class AB amplifier
« Reply #1 on: April 20, 2021, 07:18:47 pm »
Hello Dan, any possibility to purchase some PCBs please?

Offline magic

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Re: PCB's of Ampslab C300 Class AB amplifier
« Reply #2 on: April 20, 2021, 07:40:02 pm »
I know it's a necro thread, but...

Is it just me or does the VAS overcurrent protection scheme (Q9 and thereabouts) look a little fishy?
As in, it's gonna blow up Q8 :-//

Offline floobydust

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Re: PCB's of Ampslab C300 Class AB amplifier
« Reply #3 on: April 20, 2021, 09:57:32 pm »
R19 is only 10R so I don't expect Q9 to turn on until things are smoking. It seems to be 33R in the updates, but still very high current.

These copies of Self's Blameless design are plentiful and it's missing a Baker clamp, will hang up if driven into clipping and compensation capacitors everywhere usually mean the stability is not as needed.
I'd expect VAS Q8 to get damaged, other copies of the Blameless added a current-limiting resistor on its collector as well as a Baker clamp for it.
Essential on the PCB layout is taking NFB right off the output, not a long pcb trace away as the design should be able to do better than 0.01% THD.

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