Power supply 1st capacitor.

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pre65
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#1 Power supply 1st capacitor.

Post by pre65 »

Is there a general rule of thumb to estimate the value of a first cap (before a choke) to make it run as cap input ?

Or, does one put various values in a PSU designer sim and see what happens ?
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Nick
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#2 Re: Power supply 1st capacitor.

Post by Nick »

Not sure, depending on how you define choke input, it may be valid to say that any cap means its cap input, but if we define choke input such that the current drawn from the transformer is continuous (but not steady) it may be the point where the peak current through the cap exceeds the current through the choke, but I dont feel up to trying to work that out at the moment (if ever). And I think it would also depend on the load current being pulled.

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#3 Re: Power supply 1st capacitor.

Post by IslandPink »

By all means try things in PSUD.
I remember with the Aurora amps years ago, Lynn O described caps in the range 1uF to 1.5uF as 'transitional' . Also Brian Sowter regarded his job of supplying the chokes as 'not choke-input' if the cap was 1uF or larger . I think you'll find the circuit is more or less 'cap input' by 10uf.
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Mike H
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#4 Re: Power supply 1st capacitor.

Post by Mike H »

I have used a small value cap, and it has the effect of turning the choke into a tuned circuit. (The large value cap after the choke making a low impedance AC path to complete the circuit.) That in turn can have the effect of increasing the final Voltage to be higher than what you would normally get with pure choke input. In other words can be 'tuned' by varying the value of the cap.
 
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Paul Barker
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#5 Re: Power supply 1st capacitor.

Post by Paul Barker »

Small cap usually improves sound. Morgan Jones first book has section on snubbers across any choke of 220nf I think it was. That is from each end to ground, parallel on the output to the firts reservoire cap. up to 1/2 uF firts cap usually remians in choke input but stops cheap choaks rattling. 1/2 to 1 strats raising voltage between 0.9 and 1.414. Sometimes a technique to fine tune voltage, not a bad idea.
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Mike H
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#6 Re: Power supply 1st capacitor.

Post by Mike H »

Yes that sounds familiar, reduces buzzing of the choke. I've done this, but details lost in mists of time...
 
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