John Curl's Blowtorch preamplifier part II

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I use chokes as well BUT they are both more capable of generating interference and receiving it than any other component. When close to a rectified supply it could be a can of worms.

A well designed RF choke can have good inductance to very high frequencies. Adding a core will lower the dcr and raise the inductance, but for a more limited frequency range and current level. They are no less tricky to use than active components, and possibly harder since they are mostly custom made for an application different from yours.

Cut and try seems to be the best way to get results. Resistive damping externally avoids excess DC loss. An RC can be used effectively as well. And adding a resistor in series insures that the impedance will be positive and resistive at a minimum. Look at the self resonance of the inductor like that of a cap.
 
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PMA said:


You have to shield them.

Lots harder to do than it may seem to be. And the shielded chokes are limited in size and value. A Mu Metal shield around a power inductor may work, or it may saturate real fast if the current is high.

Actually this is a real problem for AC line filters. If the load is large (power amp with small conduction angle pulling 30 0r 40 A peak charging currents) the line filter chokes will saturate at the line frequency modulating any RF on the line making it worse that it might have been before the choke was inserted.
 
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PMA said:
I know. But any mains filter, e.g., should be placed in a shielded box with feedthroughs. Al box like Blowtorch, would help, 10 mm Al is about 50Hz skin depth and electric field is suppressed almost completely.

But we are probably off topic again, aren't we?

I think we are on topic, its very "blowtorchy" to obsess over removing a residual source of noise. Thanks for a reason for 10 mm AL other than mass and metal sculpture. Be sure to use good feedthrough caps to get in and out of the box. Does anyone make film feedthrough caps?
 
Hi 1audio,

just reading an old TAS from 1980 about the Spectral MS-One Series Three preamp and presuming you are Demian Martin the circuit designer.

If so can you share any circuits that:

1. might be buildable and of good performance

2. could promote reasonable discussion

3. won't do you out of any income

I know it's a tough one but who knows?

thanks,
sp
 
syn08 said:
.....................Strictly from a datasheet perspective, an IRF MOSFET matching part is not IRFP240/IRFP9240 but IRFP244/IRFP9240. This should be theoretically at around the same performance level as the Toshiba pairs, of course this has to be experimented and confirmed. These IRF pairs are about three times less expensive than Toshiba!...........

IRFP 240 / IRFP 9140
 
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nicoch46 said:
Any one can point a book/Ebook on audio psu ?

just to try understan in a basic manner but correct this threads !:D


Since a psu is a psu, you won't easily find an engineering book on 'audio psu', but you'll find easily a lot (hard paper books at least) about 'psu'. Look up books by Lenk or Gottlieb for instance

Jan Didden
 
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