Bob Cordell's Power amplifier book

Hi all. On page 383 of Bob's book he talks about film type snubber capacitors. I was just wondering are tantalum capacitor ok to use or are film type capacitors better. If so please provide a explanation and details so I can understand.

Thanks.



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if the ceramic have a black cap then that usually means NP0/C0G
Those size of beads in 100pF and with a black cap would be NP0/C0G

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You don't have capacitors in a bridge rectifier.
Do you mean what type of capacitors do you need to create a damping Zobel across the transformer inductance?
The resistor absorbs the energy of the ringing and the capacitor helps prevent the resistor from blowing up.
 
Hey Stu, snubber caps are best metalised film or film foil with low resistive losses. At the mains frequency the relatively high Xc protects the snubber resistor from too much continuous current and at the much higher secondary resonance frequencies the much lower impedance allows the resistor to dissipate all the ringing energy. For a short time the resonant current could be quite high so the cap needs to have a reasonable pulse current rating.

Capacitors with an X or Y rating for direct connection to mains are very reliable for connection across transformer secondary, are readily available and fairly low cost although they are fairly large.
See RS Stock No. 869-7469
This is 250Vac, 100n X2 with pitch of 15mm

Cheers
John
 
I read a bit of that thread awhile ago I will re vist it and look into this further. However I fine it very puzzling that nobody can offer a single part number of a snubber capacitor that they have actual used in an actual amplifier build....

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I used this exact capacitor in a CRC snubber connected across the transformer secondary, of an actual amplifier build. Carefully note: the capacitor was NOT connected in parallel with a diode; it was connected in parallel with the transformer secondary. This particular capacitor was mentioned by name in the Quasimodo design note, shown below.

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Understood. I know what that feels like. I am in the midst of moving the family from London to Miami and having to do a stint in New Zealand while my immigration visa is processed.

As a guy stuck with balanced sources I'm still hoping the second edition devotes space to fully balanced input stages etc so I can save the space required by my implementation of Self's balanced to single-ended input board....