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Old 27th September 2013, 03:36 PM   #1
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Default Using a regulated ps for a power amp input stage.

In the first watt amplifiers we have the input stage being feed from the unregulated power rails.

I like the idea of using a regulated supply for powering the input stage of the amp, and then having a separate unregulated supply for the output stage which is more tolerant as far as I understand.

From reading around I believe that cascoding can be seen, to some extent, as some sort of regulation, since it protects the input transistors from higher voltages in the power rails, does it also improve the quality of the supply?

What would be a simple regulator one could piggyback into an f5 board for example?
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Old 27th September 2013, 03:51 PM   #2
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cascoding is no way the same as regulated PSU. the cascoding just shave of some amount of the voltage. the cascoded voltage is determined by the rail voltage and will swing paralell to it.
a simple LM317/337 regulator is the easiest way to regulate the inputstage. or LM78xx/79xx.
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Old 27th September 2013, 04:02 PM   #3
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On some amplifiers like the F5 and J2 you cannot separate the main rails from
the front end as the output devices are operate "Common Source" and the
front end develops voltage to drive them referenced to the main rail.

Otherwise, it's perfectly OK to regulate the front end supply.

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Old 27th September 2013, 04:06 PM   #4
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If construction of amp in question allows it , then reg is welcome

edit: for second time today , Pa was faster

so , considering that Big Man is in thhe office , I'm going to Lalaland now , to squeeze that flu out
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Old 27th September 2013, 05:01 PM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AudioSan View Post
cascoding is no way the same as regulated PSU. the cascoding just shave of some amount of the voltage. the cascoded voltage is determined by the rail voltage and will swing paralell to it.
a simple LM317/337 regulator is the easiest way to regulate the inputstage. or LM78xx/79xx.
The cascode could be referenced via a resistive voltage divider between rail and ground. That type would swing with every change in supply voltage including interference.

The cascode can also be referenced to a fixed voltage set some way above the signal ground, or to the LTP emitter voltage and be virtually impervious to variations in supply voltage and interference.
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Old 27th September 2013, 11:01 PM   #6
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Build yourself a shunt regulated BA3
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Old 28th September 2013, 05:41 PM   #7
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So I've been going throught the ba3 article and schematic, and due to my limited electronics knowledge can't seen to understand the need for the capacitor on the output of the ba3 input stage. the circuit is quite similar to the f5 and it doesn't have that specific cap. it is because of not having a feedback loop?
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Old 29th September 2013, 07:09 PM   #8
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Do you mean at the "D" output? Because that node would be connected to the P channel bias of the BA-2 output stage. Or N Channel bias on BA-1 output stage
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Old 29th September 2013, 07:20 PM   #9
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Yes, I mean the D output, but it is in the signal path right?
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Old 29th September 2013, 10:37 PM   #10
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Yes.
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