Recommended cap for PSU bypass

[Strikkflypilot]

Hi guys.
So I finally "finished" my build.
http://bottlehead.com/smf/index.php/topic,6330.0.html
Just one more thing makes me want to pick up the soldering iron again.
There has been tall of bypassing the cap on terminals 12-13.

So I ask, do You have an advice on which to choose?
I have looked at these two:

http://www.ebay.co.uk/itm/Mundorf-MCap-EVO-SilberGold-Ol-Oil-2-2uF-450V-Audio-Kondensator-capacitor-853802-/360868961485?pt=Lautsprecher_Selbstbau&hash=item5405775ccd

And this one:

http://www.ebay.co.uk/itm/Mundorf-MCap-SUPREME-SILVER-OIL-2-2uF-Kondensator-capacitor-Silber-Ol-852557-/360530938515?pt=Lautsprecher_Selbstbau&hash=item53f1518a93

Maybe I should look elsewhere completely?

[Loon]

Replace it entirely with one of these:

http://www.partsconnexion.com/capacitor_film_clarity_tc6.html

[JamieMcC]

I found fitting cheap standard 2.2 film helped but was no comparison to the improvements gained from fitting a choke and replacing that last electrolytic cap with a big film. Cost wise this could most probably be accomplished for a similar in cost to a boutique 2.2 uf even with buying a new big film cap. The guys here walked me trough the choke fitting process in the thread below. 

http://bottlehead.com/smf/index.php/topic,6030.0.html

[Strikkflypilot]

Thanks guys!

Guess I'll try for the choke, then, Jamie:)
Nice work for the autumn.

[Strikkflypilot]

Ok.
I just pulled the trigger on a Triad C7X 😀
I understand it is supposed to replace the resistor between terminals 12 and 13.
Now I am considering a couple of options for the cap. I have looked at Mundorf Mcap 250v 220 uF, Mundorf EVO 250v 220 uF and Janzen cross cap 400v 220uF. Do these look good to You or should I look at something else?

[JamieMcC]

Before you pull the trigger on a big cap keep a close check on the dimensions as you start to run out of room real quick especially depth wise there are some discussions on the forum which mention the use of a smaller uf value with the  choke installed. I only installed the big 200uf because I already had it. A capacitor with a smaller diameter would really be advantageous in keeping all internals within the enclosure. Otherwise they can start to hang out the bottom and you will end up requiring some larger feet to increase the height of your Crack.

[thomas27]

Looks like a cool mod!

Is there an optimum placement for the choke to minimise interactions with PT? (would there be significant interactions?)

thanks

[JamieMcC]

I'm not sure on that one perhaps a good question to post on the technical bb.  A google image search for "bottlehead crack choke" shows a variety of Crack builds with different choke mounting positions. When fitting mine I wanted to keep the through top plate fastenings out of sight so went with mounting the choke behind the transformer. 

[Strikkflypilot]

Thanks gain, Jamie.
Wouldn't want too much to hang out the bottom.
I'm not in so much of a hurry, so I'll wait for the choke and see what I can fit in there.

I am right, though?

I jst remove the resistor and cap between 12 and 13 and replace them?
250v is enough?
And finally, maybe I'll notice an improvement first just replacing the resistor.

[Paul Birkeland]

I jst remove the resistor and cap between 12 and 13 and replace them?
250v is enough?

That resistor has to stay.
The stock caps are 250V.

[JamieMcC]

If you have a read through the thread in the link below you will find it covers quiet a few questions and answers about installing a choke.

http://bottlehead.com/smf/index.php/topic,6030.0.html

[Strikkflypilot]

Thanks guys.
I thought chokes were used instead of resistors.
Have read the thread twice, Jamie, but sometimes hard to erase a false presumption☺
I understand they are run in paralell instead.

So to put it real easy for me, I remove the electrolytic cap from 12-13 and solder in a choke and a film cap in parallell to the resistor on 12-13?

Oh, and the orientation of the choke is important?

[JamieMcC]

Just caught up

The choke replaces the resistor 270ohm 5W (square white cement resistor) between terminals 13L and 15L the one shown at the top of page 28 in my build manual. This is the one I removed

The smaller resistor between 12 and 13 needs to stay as for safety it discharges the Cracks capacitors after power has been turned off.

I made the same mistake the schematic helps identify this.

Yes the electrolytic cap between 12-13 is the one commonly replaced with a film alternative.

The C7-X choke did not require orientating any particular way round.

[Strikkflypilot]

Fantastic explanation, Jamie.
Even I can understand it:).
Now to wait for the choke:(

[JamieMcC]

I was looking for something else and came  across this post from PB

"Re: Crack Upgrade Path?

In the power supply, fitting three 220uf film caps will be tough. Instead, run the stock first and second caps with the resistor between them, then use a Triad C7X and a 10-20uf cap after. This will impart 90 percent of the benefits of big film caps without the crazy space requirements. The C7X should knock the noise down enough to get away with this."

http://bottlehead.com/smf/index.php/topic,776.0.html

I did try a 89uf epcos film cap that I had in that position over the weekend and it seemed fine.