Replacing the last power supply cap
- Thread starter adamct
- Start date
Grainger49
New member
Adam,
Did the auction say "Motor Start" capacitor? What voltage rating did they have? What voltage will be on them?
I should point out that capacitors have a surge rating and a steady state rating. That is one of the differences between a start, which accounts for the surge, and run capacitor that is expected to be used in steady state AC applications. That also brings up that the demonstration was with AC, a power supply is DC.
So I'm still at the try it point.
Did the auction say "Motor Start" capacitor? What voltage rating did they have? What voltage will be on them?
I should point out that capacitors have a surge rating and a steady state rating. That is one of the differences between a start, which accounts for the surge, and run capacitor that is expected to be used in steady state AC applications. That also brings up that the demonstration was with AC, a power supply is DC.
So I'm still at the try it point.
Also, I'm just wondering...in the video, they specifically said that motor start caps are only rated for AC. I took that to mean "don't use these for DC", not "the DC rating isn't specified" (which would imply that if you knew the DC rating, and they matched your purpose, they would be OK).
Is there a way to test these outside of the Crack? I've got a DC power supply. Actually several of them, but they are admittedly relatively low voltage (one goes up to 12 or 18V, the other is 34).
Is there a way to test these outside of the Crack? I've got a DC power supply. Actually several of them, but they are admittedly relatively low voltage (one goes up to 12 or 18V, the other is 34).
Grainger49
New member
Ok, rated for 450V AC can, but doesn't necessarily, mean 636V DC. Since we are talking about Crack here, the steady state DC is 170V. The AC from the power transformer is 150V but paralleled to give double the current capability.
I'm still at try one to see. Otherwise what are you going to do with it? Throw it away? Wouldn't you want to see if it explodes first? Protect your eyes and face.
I'm still at try one to see. Otherwise what are you going to do with it? Throw it away? Wouldn't you want to see if it explodes first? Protect your eyes and face.
Grainger49 said:
I'm pretty sure my mother warned me about guys like you! And I sense strong potential for you to be my wife's new best friend when she gets the payout on my life insurance policy...
I guess I'm OK testing them, but I would rather do it someplace away from the Crack...and my house...and my face, eyes and other body parts I've grown rather fond of...hmmmm.....
I have a story about that... When I was playing around with the "secondary" crossover for my subwoofer, I was using one of the 220R 1/4 watt resistors from my stash to experiment running parallel with a 22uf cap to crossover about 40hz. The resistor didnt seem to get hot during normal low/medium level listening, so I left it there. One night we were watching a blu-ray that had some good explosions etc and there was a flash and a pop from the sub amp area. It was such a tiny resistor I really didnt care if it exploded like that. Kind of fun actually! - so I put another one in...
I dind't seen anybody mention it, so I will say again that motor start capacitors have no place in any tube circuit (though I think they would be OK in a speaker crossover).
No worries Adam. At one point, I accidentally used a couple of motor start caps that weren't well labelled. Four of the twelve blew up all at once. I was running them with just under 200V DC total, across a string of four caps per bank that had 165V stamped on them.
Grainger49 said:
...'splain this more pleeze.
Is this something that would be suitable for the Crack? Or any other Bottlehead headphone amps?
Also, when I install the oilers in place of the last power supply cap, do I need to / should I install a bleeder resistor? If so, what values are recommended, and where do they go?
Best regards,
Adam
Whoa, it's not a bleeder. Don't do this until you better understand what it is. The idea was from Paul Schwerman, aka Voltsecond. He simply split the single final filter cap into two, with one supplying each channel. The resistor was an additional "R" to create an additional pole ,i.e., RC, with the added cap. I imagine that there is a link to the original article somewhere.
Sorry, I should have been clearer. I was combining two thoughts in one post. To clarify:
1. I was asking Grainger to explain his reference to the PDMPS.
2. I plan on installing two 100uf motor run caps in place of the last electrolytic in my Crack. I'm wondering whether I need to install a bleeder resistor for safety purposes.
Regards,
Adam
1. I was asking Grainger to explain his reference to the PDMPS.
2. I plan on installing two 100uf motor run caps in place of the last electrolytic in my Crack. I'm wondering whether I need to install a bleeder resistor for safety purposes.
Regards,
Adam
Grainger49
New member
The PDMPS is well explained in text and schematics here, it is VoltSecond's site:
http://www.siteswithstyle.com/VoltSecond/PDMPS/pseudo_dual_mono_foreplay.html
You turn a CRC filter into a CRCRC, with an additional RC for each of the channels. Hmm, that isn't clear. So the stock CRC stands. After which you attach two 1k ohm resistors. Each of those feed another 220uF cap, one end of each cap grounded, the other end attached to the 1k resistor and feeding the power supply for each channel. What it does is adds a third stage dedicated to each channel. It is a good thing if you also make the last cap a lower ESR cap. Motor Run and Film caps are good here. I am not looking at the schematic here but if the second stage Crack power supply cap is a 220uF you can add a film 150uF and it will make a positive difference.
http://www.siteswithstyle.com/VoltSecond/PDMPS/pseudo_dual_mono_foreplay.html
You turn a CRC filter into a CRCRC, with an additional RC for each of the channels. Hmm, that isn't clear. So the stock CRC stands. After which you attach two 1k ohm resistors. Each of those feed another 220uF cap, one end of each cap grounded, the other end attached to the 1k resistor and feeding the power supply for each channel. What it does is adds a third stage dedicated to each channel. It is a good thing if you also make the last cap a lower ESR cap. Motor Run and Film caps are good here. I am not looking at the schematic here but if the second stage Crack power supply cap is a 220uF you can add a film 150uF and it will make a positive difference.
My 100uf oilers arrived today. It may be pure folly, but I have to admit that I find them SEXY!
Can anyone answer my question above? Should I install a bleeder resistor for these caps? If so, what value/kind of resistor, and where/how should I install them?
Best regards,
Adam
Can anyone answer my question above? Should I install a bleeder resistor for these caps? If so, what value/kind of resistor, and where/how should I install them?
Best regards,
Adam
Grainger49
New member
The current bleeder will discharge all the power supply caps. It usually is a 249k Ohm resistor connected from somewhere in the CRC chain to ground.
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