Replacing the last power supply cap

[adamct]

Otherwise what are you going to do with it?  Throw it away?  Wouldn't you want to see if it explodes first?

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.....

[earwaxxer]

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...

[adamct]

LOL, too funny!

[Paul Birkeland]

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).

[adamct]

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).

My wife is decidedly disappointed that I won't be trying Grainger's experiment. She was already looking for real estate in Monte Carlo...

Thanks for saving me from my foolish ways, Paul!
Adam

P.S. Eric, why are my estrogen levels suddenly rising?

[Paul Birkeland]

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.

[adamct]

On the "OLD BOARD" there was something called a PDMPS, a third stage of filtering.  It stood for Pseudo Dual Mono Power Supply.  I did this with my FP 2 adding a couple of 100uF "Oilers" motor start caps.  I just put another 1k resistor between the mono power supply output and the oilers.  Then the two power supply rails went to the right and left channel. 

It did improve the sound.

...'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

[adamct]

Does the bleeder resistor get installed across the terminals on each cap? And I assume it should be fairly high value in order to dissipate charge quickly?

[Doc B.]

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.

[adamct]

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

[adamct]

Re: #1, above: Information on the PDMPS for the Foreplay is available here.

So now I'm just looking for guidance on #2.

Thanks,
Adam

[Grainger49]

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.

[adamct]

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

[Grainger49]

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.

[adamct]

Thanks, Grainger. Can anyone tell me if this is a metalized polypropylene cap suitable for use in the Crack's power supply? I think it is, but confirmation would be welcome...

Thanks!