power ratings of resistors
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 4th August 2004, 05:24 PM #11 dhaen   diyAudio Moderator Emeritus     Join Date: Jun 2002 Location: U.K. Nice schematic Caps go bang when the leakage current through them is too high. That will happen if the polarity is reversed, or if their voltage rating is exceeded. Don't forget that the DC across those caps will be nearly 1.5 x the AC into the rectifier. Also the AC voltage may be 20% higher than specified with no load current being taken. I'll pray for your caps...
 4th August 2004, 05:53 PM #12 6SN7GT   diyAudio Member     Join Date: Jun 2004 Location: Sarf Koast dhaen, You beat me to it .. I couldn't get at diyAudio .. it just timed out The caps almost certainly were connected reverse polarity. The sequence of events, time line, and the consequence says this is most likely. I can hear the bubbles forming That is one of the best circuit diagrams ever, alecwek ! Assuming it's to scale, I calculate the BANG to be 108.43dB spl at 1 metre
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Quote:
 Originally posted by 6SN7GT Assuming it's to scale, I calculate the BANG to be 108.43dB spl at 1 metre
Ohm's law?

Love the drawing, be careful though!

/Hugo

 4th August 2004, 06:27 PM #14 jackinnj   diyAudio Member     Join Date: Apr 2002 Location: Llanddewi Brefi, NJ A 50Kohm/20 Watt Vitreous Dale resistor is about 1.5 inches long, .6 inches in diameter, the sand cast power resistors are a little smaller. Bleeders -- you should figure that the value of the bleeder resistor will reduce the voltage on the capacitors by about 90% in the time it takes you to remove the amplifier cover -- 30 seconds -- the equation is: V(f) = V(i) * e^(-t/RC). where Vi is the initial voltage and Vf the final voltage -- let's say you are using 470uF of filtration on 400 VDC -- a 27K ohm resistor will bleed the caps by 90% in 30 seconds or thereabouts. the current drawn by the bleeder is 400V / 27000 Ohms = 14.8 ma. The power is thus (.0148^2) * 27000 = 6 watts. A 10 Watt resistor will accomodate a big swing in the supply voltage. this is a lot of power to burn, however.
 4th August 2004, 08:14 PM #15 alecwek   diyAudio Member   Join Date: Jul 2004 Location: dk ok... now that u mention it...the caps were connected in revers.....man!!!its cause when i kept flipping the breadboard round ...up down....alittle to the left!!!...i guess i must have gotten the rails the wrong way round........i drew schematics on the non copper side before soldering so i had to keep flipping to solder.....man i gotta learn how to make pcb.....also u should see how crap my finished peices look...hmm...ah well..... what is the best looking.....quickest.....(cheapest )way of making curcuits....pcb look a bit expensive and complicated....plus how on earth do you sheild pcb lines..........
 4th August 2004, 08:16 PM #16 alecwek   diyAudio Member   Join Date: Jul 2004 Location: dk oh and thanks for all the help so far
 4th August 2004, 08:38 PM #17 6SN7GT   diyAudio Member     Join Date: Jun 2004 Location: Sarf Koast Ah ha!, I think we got to the bottom of the exploding caps problem OK. So that's good. I agree, you have to be careful with breadboard designs and remember which side you are working from. Why do you want to shield PCB lines ? Because the interconnect wiring is effectively 2D, crosstalk (interference) can be managed reasonably well. You have something in mind I guess ? Do tell.
 4th August 2004, 09:54 PM #18 alecwek   diyAudio Member   Join Date: Jul 2004 Location: dk well its just cause i heard,....from one of the thousands sources (that are found in great abundance in electronics) that high voltage lines should be sheilded ...and also high voltage points...caps..etc...i guess cause of noise, also i could imagine it being ......ummm.....healthier, to keep power rails and high voltage ,current lines sheilded...less chances of accident...but man, electronics is polluted with so much good advice its hard to get a grip on it all....

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