Coupling capacitors
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sb****33
diyAudio Member

Join Date: Jan 2009
Coupling capacitors

Hello everybody

I'm just curious about the values in this preamp : C4-C6 .22uF.
Why not 10uF like the output one C7 ?
Are they acting like low frequencies cut-off ?
There are such value in ARC SP6, for exemple.
Attached Files
 CAT_SL1_ECC88.pdf (274.1 KB, 105 views)

 29th October 2015, 09:14 AM #2 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders the coupling capacitor acts as a High pass filter when combined with the following load. The load is 1Meg in parallel to the grid input impedance. I don't know how to calculate that input impedance. If I assume it is 0.5M , then the total load after the coupling capacitor is: 500k*1000k/(500k+1000k) = 333k The turn over frequency of this single pole filter is given by F-3dB = 1 / (2 PiRC) = 1/(2*3.14*333k*220*10^-9) = 1/0.46 = 2.2Hz The response will be down by ~1dB @ 4.4Hz You need an estimate of the input impedance to allow you to check the F-3dB. __________________ regards Andrew T.
 29th October 2015, 09:16 AM #3 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders Your profile says you joined in July 2001, but under your nickname it states Jan 2009 What up? __________________ regards Andrew T.
ErikdeBest
mostly thinkerer
diyAudio Member

Join Date: Mar 2003
Location: Zürich
Quote:
 Originally Posted by AndrewT Your profile says you joined in July 2001, but under your nickname it states Jan 2009 What up?
Weird indeed If one clicks on profile, the name Stan 33 something appears, with last activity in 2006.
__________________
my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!

sb****33
diyAudio Member

Join Date: Jan 2009
Quote:
 Originally Posted by AndrewT the coupling capacitor acts as a High pass filter when combined with the following load. The load is 1Meg in parallel to the grid input impedance. I don't know how to calculate that input impedance. If I assume it is 0.5M , then the total load after the coupling capacitor is: 500k*1000k/(500k+1000k) = 333k The turn over frequency of this single pole filter is given by F-3dB = 1 / (2 PiRC) = 1/(2*3.14*333k*220*10^-9) = 1/0.46 = 2.2Hz The response will be down by ~1dB @ 4.4Hz You need an estimate of the input impedance to allow you to check the F-3dB.
OK, Andrew.
What about C6 and C7 ?

sb****33
diyAudio Member

Join Date: Jan 2009
Quote:
 Originally Posted by AndrewT Your profile says you joined in July 2001, but under your nickname it states Jan 2009 What up?
what nickname ? stan_33 ? I don't know who is it. I never entered that name.

 29th October 2015, 11:24 AM #7 DF96   diyAudio Member   Join Date: May 2007 I seem to recall other people finding that the site software can confuse people with what it considers to be similar IDs. stan_33 and sb****33 both start with 's' and finish with '33', so easy for a dumb computer to think they are the same person! Raise a query in the web problems forum.
 29th October 2015, 11:31 AM #8 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders is "****" appearing because he typed ****, or because the Forum recognises that as a banned word and has overwritten his entry? __________________ regards Andrew T.
 29th October 2015, 11:36 AM #9 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders C7 is coupling capacitor, but the output looks wrong. C6 is a bootstrap that creates one of those totem pole thingies that I don't understand. __________________ regards Andrew T.
 29th October 2015, 12:05 PM #10 Merlinb   diyAudio Member     Join Date: May 2006 Location: Lancashire R2 is incorrect. It should be much larger, say 100k to 1Meg.

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