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Old 28th December 2005, 12:04 AM   #1
Joseph0 is offline Joseph0  United States
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Default cathode capacitance on anode follower

attached is a transfomer coupled anode follower circuit from an AudioNote DAC (2.1x BAL).
the original capacitance connected to the cathode pins of E188CC is 470uF.
I was thinking of trying two BG N 470uF caps in super E: 940uF.
The circuit is hardwired however and I'd rather get it right the first time.
What does changing this capacitance do technically?
What does changing this capacitance do sonically?
Thank you to anyone who responds.

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Old 28th December 2005, 02:06 AM   #2
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Hi Joseph,

looks like a common cathode buffer using parallel triode sections, with self bias mmm. anyway the caps I take it you are referring to are bypass capacitors accross the 180R cathode resistor. the value is chosen to effectivly increase the AC gain ie audio gain and mostly effects the lower frequency response. that is the point is where Cx reactance equals the cathode resistance. so increasing the value effectivly decreases the low frequency response, to a point.

thats the technical.

In reality I'm not sure if this translates to better sound given that it is large electrolytic in the the signal source and some people would say it would be better avoided.

what you have 470uf Cx @ 20hz ~ 17r almost 1/10 of Rk

after you change it to 940 Cx @20hz ~ 8.5r almost 1/20 Rk

Personally I don't think I could tell the difference.
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Old 28th December 2005, 03:20 AM   #3
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Hi Joseph

I re read this and it made sense at the time but!


so increasing the value effectively decreases the low frequency response, to a point.

decreases the -3db point not the low frequency response so should read

so increasing the value effectively improves the low frequency response, to a point.

Robert
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Old 28th December 2005, 04:54 PM   #4
Joseph0 is offline Joseph0  United States
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thanks for the help, Robert.
now, say I'm using 470uF BlackGate N, non-polar, 'completely symetrical', capacitors and have accidentally reversed the leads, hooking up the +, long lead, to the ground, and the -, short lead to the signal.
I don't feel like redoing it..
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Old 28th December 2005, 10:46 PM   #5
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Hi Joseph,

Ok I don't know that brand/type, however if it is a non polorized cap there should be no notion of polarity. the long and short leads are simply a function of manufacture i.e. same assembly as regular caps.

incidently is 470uf the standard value?
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Old 29th December 2005, 02:25 AM   #6
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Hi,

Quote:
now, say I'm using 470uF BlackGate N, non-polar, 'completely symetrical', capacitors and have accidentally reversed the leads, hooking up the +, long lead, to the ground, and the -, short lead to the signal.
Since the cap is a non-polar type there is no actual polarity so from a mere electrical POV it doesn't really matter which end's up....
Mind you, those Black Gates defy all laws of physics so be ware....

However, one of the leads is connected to a shielding foil which is directional. You'd want that foil connected to ground (-) or it won't have much of a shielding effect.

No big deal either way but just so you know.

The Jelmax "Tech sheets" are probably written by people lacking any technical knowledge, stink at English or any random combination of the above.
IOW, things can get confusing................

Now, regarding your question about "Super Eing" the bypass cap(s), assuming that's what it is as my reading of Modigliani paintings sux big time, I wouldn't bother.
There must be better places to waste money on..... Must be.

Besides, if you put two caps in series the total capacitance does not double but halves...
Unless the kids at Jelmax pulled a magic rabbit that is, in which case the value would remain the same. At best.

It's been a while since I last amused myself wading through their technobabble so you'd better measure the actual capacitance before you hook up those caps that way.....

Did I confuse anyone?? Probably just myself......................

Cheers,
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Old 29th December 2005, 02:39 AM   #7
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Quote:
Originally posted by fdegrove
Did I confuse anyone?? Probably just myself......................
Articulate, cultured and of subtle good humour, as I'm sure many appreciate.
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Old 29th December 2005, 10:55 AM   #8
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Frank,

As always, very informative and straight to the point.



JojoD
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Old 29th December 2005, 01:40 PM   #9
Joseph0 is offline Joseph0  United States
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with two BG N's in series, the capacitance doubles. I've measured it.
BG N's may be a waste of money, but they sure sound good.
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Old 29th December 2005, 10:57 PM   #10
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Hi Joseph,

You indicated that the caps would be in parallel as per the drawing, what I am intrigued with is the sub 1 hz -3db point your trying to achieve using increased k bypass capacitance. What was the original value? I'd guess somewhere between 47uf and 100uf??

Have you considered this might cause issues with short term drift, perhaps saturation of the O/P transformer core I don't know the specs on the units fitted.

Sy had a good response on this subject about a month ago he indicated too much LF response might in itself cause problems and was a good read.


fdegrove,

I didn't realize these black gate caps were sooo expensive this means I have to choose between ofc cable or BG caps ;o((

Robert
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