Cap Multiplier: Before or After the Regulator? - diyAudio
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Old 25th June 2015, 02:48 AM   #1
mlackey is offline mlackey  United States
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Default Cap Multiplier: Before or After the Regulator?

I've seen PS circuits with simple cap multipliers used before and after a LM317/337 regulator. Does one configuration provide "better performance" than the other?

Oh,and BTW, the application is a class A headphone amp biased at around 100mA, maybe 125mA. Needless to say, "constant current", which simplifies things considerably.
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Old 25th June 2015, 08:04 AM   #2
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cap multiplier doesn't make much sense after regulator as then there is not much use for the regulator. Cap multiplier is not a regulator. Question is what is that you need?
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Old 25th June 2015, 08:36 AM   #3
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by mlackey View Post
........................... the application is a class A headphone amp biased at around 100mA, maybe 125mA. Needless to say, "constant current", which simplifies things considerably.
ClassA is not constant current.

There are a few (very few) ClassA circuits that are constant current, but they are rarely used.

I posted a reply about an example just a couple of days ago.
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Old 25th June 2015, 10:02 PM   #4
mlackey is offline mlackey  United States
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Quote:
Originally Posted by AndrewT View Post
ClassA is not constant current.
<snip>
I posted a reply about an example just a couple of days ago.
Did not know that. But then again, the only thing that surprises me is how little I do know.

Looked at past posts, didn't see anything obvious. Can you provide a link? I've read the Cordell, Self, Slone books (AKA self taught) and from those have the impression of "constant current". If that's wrong, I need to fix it ASAP.
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Old 26th June 2015, 08:45 AM   #5
AndrewT is offline AndrewT  Scotland
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read the F5x. It is true constant current. And that was used to allow a much simpler PSU to do the job of supplying current.
One or two variations of the F5T are constant current.
There is a single ended topology that is constant current, but the majority are not.

Look at any push-pull amplifier and trace the route the the speaker current follows from PSU to speaker... and back.
Now do a thought exercise: The speaker current varies. What does that do to the PSU current?
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