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Old 1st March 2005, 02:17 PM   #1
Stefano is offline Stefano  Italy
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Default choke dimensioning for class A

Hi to everybody, I know it's an old question, but I have to know if for a class a amplifier (zen v4) it's really important that the power supply choke is air-gap since the dc current is costant, it is possible to use a standard ferrite coil of 2-3 Henry, 0.1 ohm?
Has anyone of tried something like this?
Charls Hansen, Nelson Pass?
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Old 1st March 2005, 08:41 PM   #2
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An awful lot of inductance...that thing must be refrigerator sized?

Whether or not the DC is constant, it needs an air gap so the current doesn't saturate the core, which reduces or eliminates the effectiveness of the AC factor (i.e. reduced inductance).

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Old 1st March 2005, 08:48 PM   #3
MRupp is offline MRupp  Germany
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I am using a choke-input power supply on my ZEN V4 but I went somewhat over the top and got chokes with 300mH, 0,75Ohm, and btw. no airgap (10+ kilo’s a piece). They do work fine though. I use off the shelf 60V toroids and get ca 55 Volts.

The chokes need to have a minimum or “critical” inductance for a true choke-input supply with a continuous current draw over a full load cycle and power factor correction. The formula I have is Lc=1.2*Vout/Iout for 50 Hz operation (Lc=Vout/Iout for 60 Hz operation). So for 50 Volts and 2 Amp this is 30mH minimum.

Note that the ZEN V4 has a variable current draw so you may actually need a higher inductance, how much more is dfficult to say. Use PSU Designer II from Duncan amplification and play with different values say between 30 and 60 mH? One more point, the voltage of a choke supply is 0,9 * V rms when loaded, but goes up to ca. 1.4 * Vrms when not loaded, so for safety reasons you should use caps with higher voltage ratings (80 or 100V would be a good idea).

Martin.
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Old 1st March 2005, 08:48 PM   #4
MRupp is offline MRupp  Germany
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Sorry, I should read more carefully, I think you want a normal pi filter supply, CLC. Her you should be able to use air core inductors, say 2,2mH.
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Old 3rd March 2005, 07:33 AM   #5
Stefano is offline Stefano  Italy
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Sorry, my error, I mean 2mH..., tqank you very much for your replies Sch3mat1c, I will try your way!
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Old 3rd March 2005, 07:39 AM   #6
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Default low impedance

might be a good idea to keep power supply impedance as low
as possible
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