What Caps?

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Offline johnsonad

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Reply #15 on: July 03, 2013, 02:19:36 AM
PJ/PB, can I use a 100v cap here?

Aaron Johnson


Offline Paul Birkeland

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Reply #16 on: July 03, 2013, 04:25:35 AM
I probably wouldn't, though it's possible that it wouldn't cause any problems.  It's tough to ignore that even the regulated supply is well over 100V.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Doc B.

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Reply #17 on: July 03, 2013, 06:36:39 AM
Best answer is to do what we did - listen to a variety of caps:

Theory 1 - LF cutoff and phase shift suggest that a 5Hz corner is close enough to zero. 260K at 5Hz is 0.12uF.

Theory 2 - The cap reactance should be no more than the output impedance at the lowest hum frequency, to minimize the chance of capacitive hum coupling. 600 ohms at 60Hz is 4.4uF

#3 not-a-theory - we tried a bunch and thought the bass was best at 10uF or more.

YMMV.

I know this may seem out of character, but I actually measured that 10uF was around the smallest we wanted to go for best bass extension into a typical 50K-100K load, on a scope.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline HF9

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Reply #18 on: August 20, 2013, 07:27:15 PM
PJ/PB, can I use a 100v cap here?
Trying not to be a PITA, but would 200v suffice for the 10uF caps in the PreBee/Mainline? I'm eyeing up a particular Russian PIO model that I might be able to shoehorn.

My DIY Audio Electronics Blog: DIYAudioBlog.com


Offline Paul Birkeland

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Reply #19 on: August 20, 2013, 08:18:30 PM
200V is pretty marginal based on startup voltage, but operating voltage will be much lower.

In the BeePre, the 300B's warm up very quickly (unless they are old and crusty), so the voltage across the 10uF caps will pop right down to ~100V.  If you have no 300B's and no EL84's plugged in, you'll put more than 200V across those caps...

In the Mainline, everything warms up slowly.  The 10uF caps will have more than 200V across them for quite some time, I'd say 15-30 seconds every time you turn the amp on.

I don't think I would worry a whole lot about either case, but those startup spikes may decrease the life of your 200V caps.

-PB

(PS - the Russian military caps are "noted" for having tolerance to higher voltages, but I don't think anybody has abused one to the point of failure, so no hard data really exists)

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline HF9

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Reply #20 on: August 21, 2013, 04:26:27 AM
Thanks for the great info PB, I appreciate it  ;D

My DIY Audio Electronics Blog: DIYAudioBlog.com


Offline Paul Joppa

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Reply #21 on: August 22, 2013, 04:57:38 PM
Just a quick note here - non-electrolytic capacitor voltage ratings are related to lifetime; as an example suppose 20% over-voltage reduce the lifetime by a factor of 10. So a 100,000-hour cap will only last 10,000 hours. Testing to destruction for a minute or a day will never detect this. I see too many such tests "proving that a cap can exceed its ratings".

Paul Joppa


Offline HF9

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Reply #22 on: September 25, 2013, 08:22:10 AM
I bit the bullet and ordered some Jupiter HT 10uf 300V caps. I've had good luck with Jupiter in the past so hopefully they match up well with these fancy new bottlehead kits :)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.hificollective.co.uk%2Fimages2%2Fjupiter_flatstack_100v_350.gif&hash=5170861a297995ea7fa6f417fd7fb16692fe14d3)

My DIY Audio Electronics Blog: DIYAudioBlog.com


Offline Paully

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Reply #23 on: September 25, 2013, 11:23:39 AM
Then there are people like me.  Read somewhere that Doc liked Auricap (might be true, might not!).  Put some in, sounded good.  Done.  I suppose I have used Teflon, Obligatto, and some others here and there but when it came to Bottlehead, it was pretty much build it with Auricap and call it good.  I never wanted to capacitor roll, I didn't even want to deal with replacing capacitors later.  So I know less about what these capacitor upgrades did only ever having upgraded the capacitors after having listened to stock in my original Foreplay II.  My point (finally) is if you want to obsess, great, if you enjoy that kind of tinkering that's great!  If not, do what I did in my Eros.  Pick a cap that has a good reputation.  Stick it in.  If it sounds good, listen to the music and call it a day.  Your call!



Offline johnsonad

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Reply #24 on: September 25, 2013, 12:48:48 PM
I bit the bullet and ordered some Jupiter HT 10uf 300V caps. I've had good luck with Jupiter in the past so hopefully they match up well with these fancy new bottlehead kits :)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.hificollective.co.uk%2Fimages2%2Fjupiter_flatstack_100v_350.gif&hash=5170861a297995ea7fa6f417fd7fb16692fe14d3)

I wish you would have contacted me.  I would have sold you mine :)

Aaron Johnson


Offline HF9

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Reply #25 on: September 26, 2013, 04:54:57 AM
Did you settle on the Russian oilers? I was definitely considering them but I figured it would be a little difficult to mount a pair of 6uf 400V KBGs on each side of the amp ;)

My DIY Audio Electronics Blog: DIYAudioBlog.com


Offline Grainger49

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Reply #26 on: September 26, 2013, 04:57:12 AM
If the Jupiter HT caps look like the ones above please post a picture.  I have no reference for size in the above photograph.  I'm curious.
« Last Edit: May 30, 2014, 10:18:56 AM by Grainger49 »



Offline HF9

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Reply #27 on: September 26, 2013, 05:06:05 AM
I'll post a pic as soon as they arrive.

My DIY Audio Electronics Blog: DIYAudioBlog.com


Offline Paul Birkeland

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Reply #28 on: September 26, 2013, 06:14:28 AM
I grabbed 20 - 10uF/160V Russian MGBO's from Bulgaria for about $2 each. Unfortunately, if I use them in all possible places in my system, I will still have 16 left, lol.

I also ordered one of the varieties of balanced input transformers, and we'll work on putting up instructions for installation.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline johnsonad

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Reply #29 on: September 26, 2013, 09:33:34 AM
Did you settle on the Russian oilers? I was definitely considering them but I figured it would be a little difficult to mount a pair of 6uf 400V KBGs on each side of the amp ;)

I did and for me they work very well. I'll find a home for the Jupiter's at some point.  Their voltage rating is too low to use them in a power amp....

Aaron Johnson