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Old 1st June 2009, 09:31 PM   #1
piero7 is offline piero7  Italy
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Default Tube PSU differences

What are the main differences in these two tube power supply? What the best choice for a tube preamp?
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Old 1st June 2009, 10:27 PM   #2
star882 is offline star882  United States
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The first one has an additional stage of filtering.
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Old 2nd June 2009, 07:37 PM   #3
piero7 is offline piero7  Italy
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Seriuosly, what the differences to mount two chokes like pic A and two chokes like pic B?
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Old 2nd June 2009, 08:16 PM   #4
star882 is offline star882  United States
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The first one has an additional capacitor. At low frequencies, capacitors are much more effective than inductors for power supply filtering.
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Old 2nd June 2009, 09:21 PM   #5
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Quote:
Originally posted by star882
[snip]At low frequencies, capacitors are much more effective than inductors for power supply filtering.

Depends on the value of the cap and the inductor.

The first has indeed an extra stage of filtering. Two stages of filtering means that the final ripple voltage is substantially lower.

Also, in the 2nd pic, you pick off your voltage from the terminals of the 2nd cap, and NOT from cap and the secondary tap! That means that your output voltage will be quite a bit lower. Too low, I would guess. Do a sim.

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Old 2nd June 2009, 10:24 PM   #6
star882 is offline star882  United States
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Quote:
Originally posted by janneman
Depends on the value of the cap and the inductor.
At lower frequencies, the values of both inductors and capacitors need to increase for effective filtering. However, large inductors are heavy, have a high series resistance, and are expensive. Large capacitors, by contrast, have low ESR.

There's a reason why passive PFC (with a large line frequency inductor) has faded away in favor of active PFC (with a small high frequency inductor and control electronics).
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Old 3rd June 2009, 12:00 AM   #7
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PSU design not allow to simulate a filter like pic B unfortunately, or I'm not able to do it?
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Old 3rd June 2009, 01:12 AM   #8
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If we assume stray capacitances are negligible (which they will be at low frequencies), the circuit will behave the same as if the second inductor was on top in series with the first.
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