CRCRC vs. LCLCLC which is better and why? - diyAudio
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Old 22nd January 2005, 03:03 AM   #1
Clarkcr is offline Clarkcr  United States
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Default CRCRC vs. LCLCLC which is better and why?

I putting together a PSU for an amplifier and am wondering if I should use large resistors to drop voltage on the rails or use toroid inductors. Can anyone tell me why I wouldn't want to use inductors?

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Old 22nd January 2005, 09:07 AM   #2
jesper is offline jesper  Sweden
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Because a LC circuit is a resonant, low loss system with possible very ugly transient responce.
However, as allways, if designed proporly, it could be a good comprimise between filter attenuation and accapteble transient responce.

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Old 22nd January 2005, 09:22 AM   #3
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Find out for yourself with PSUD 2 (search for Duncan PSUD2) and be wiser.

Sounds like you want to drop the voltage. Depending on your component values - an inductor drops the voltage AND increase utilization of the transformer (a good thing) in an LC configuration.

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Old 22nd January 2005, 12:37 PM   #4
Eva is offline Eva  Spain
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A LC cell provides 12dB/oct filtering but the L and C values have to ve carefully selected to create a damped non-resonant system, depending on inductor Rdc and capacitor ESR

The LC filter design goes more and more complex as more LC cells are added in series, it will definitely require custom-wound inductors with custom inductance and Rdc values and some minimum load resistance on the output to avoid resonance

In the other hand, a RC cell provides only 6dB/oct filtering but it will never resonate, even in case of crazy R and C values, and you can easily place several in series
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Old 22nd January 2005, 01:58 PM   #5
Clarkcr is offline Clarkcr  United States
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Thanks Eva....that's a great help!!! What is meant by ESR and Rdc values?

Would these inductors be impossible to get right in a Class A amplifier? Or would it be preferrable sense the dissipation is at a constant. I'm lacking some knowledge here, so bare with me.

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Old 22nd January 2005, 03:23 PM   #6
AndrewT is offline AndrewT  Scotland
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what kind of classA topology are you referring to.
I can recall only one that has constant current in the supply lines. All the common topologies have varying current in the supply lines and from this forum and many others I would estimate that 99% of classA amps are not constant current.
The supply rail currents are generally modulated in phase with the input/output signal.
Back to your question I would recommend further research but avoid LCRC. Some manufacturers have used this and it does suit classA or very high bias classAB. However the minimum and maximum spread in acceptable current to stay in the inductor controlled region is fairly narrow and you may as an amateur find the cost of trial & error design too expensive.
CLC should work fairly easily without having to discard too many components.
Have you considered a capacitance multiplier? JLH proposed a basic version and ESP has developed it a little further. I did read on another thread that this did not suit the sound of another classA design.
finally PSUD2 is worth using.
regards Andrew T.
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