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Old 28th January 2011, 07:35 AM   #1
Tyimo is offline Tyimo  Hungary
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Smile Capacitor questions

Hi!

I would like to ask some questions:

1. Sometimes I see in voltage divider mosfet bias circuit a
capacitor connected between the middlepoint of the voltage divider to the ground. Sometimes not.
A, Is this cap really necessary or not??
B, Should be ELKO or foil cap?
C, Is there any rule for calculating such a capacitor's value?

2. Sometimes I see "Accelerator" capacitor on the amplifier PCB, in the input of V+ to ground. Sometimes not.
Sometimes it is a few hundred uF ELKO or a couple of nF fouil cap.
A, Is this cap really necessary or not??
B, Should be ELKO or foil cap?
C, Is there any rule for calculating such a capacitor's value?

3. This is an evergreen question :-)
What kind of input cap is good?
In some cases I see ELKO in the input, but sometimes foil cap.
Which is better?

Greets:
Tyimo
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Old 28th January 2011, 08:18 PM   #2
Tyimo is offline Tyimo  Hungary
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Nobody can answer?!?
I cann't believe....
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Old 28th January 2011, 08:23 PM   #3
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You must have some patience. Most of the wise guys
around here are old and slow.

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Old 29th January 2011, 07:09 AM   #4
Tyimo is offline Tyimo  Hungary
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Yes, Master!
Maybe you could best respond?

Greets:
Tyimo
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Old 29th January 2011, 09:02 AM   #5
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I will answer 3.
No cap is better than film is better than electrolytic
There is more to it than that but i don't want to ramble on
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Old 29th January 2011, 09:06 AM   #6
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Quote:
Originally Posted by Melon Head View Post
I will answer 3.
No cap is better than film is better than electrolytic
There is more to it than that but i don't want to ramble on
37...not that old?
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Old 29th January 2011, 09:24 AM   #7
AndrewT is offline AndrewT  Scotland
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At least a third of Members are asleep at any time.
At least a third will be doing something else at any time.
Of the remainder, how many would you expect to be online when you post a question?
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Old 29th January 2011, 07:13 PM   #8
Tyimo is offline Tyimo  Hungary
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Quote:
Of the remainder, how many would you expect to be online when you post a question?
I wrote my reasking question after that I saw there was already more than 77 views....
But I am patient.
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Old 29th January 2011, 07:15 PM   #9
Tyimo is offline Tyimo  Hungary
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Quote:
No cap is better than film is better than electrolytic
It is too simple answer.
Look at Mr. Pass's designs! He also use many time ELKO as input cap.
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Old 29th January 2011, 08:57 PM   #10
Gordy is offline Gordy  United Kingdom
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Quote:
Originally Posted by Tyimo View Post
Hi!

1. Sometimes I see in voltage divider mosfet bias circuit a
capacitor connected between the middlepoint of the voltage divider to the ground. Sometimes not.
A, Is this cap really necessary or not??
B, Should be ELKO or foil cap?
C, Is there any rule for calculating such a capacitor's value?
If the voltage divider then feeds a large value resistor to the bias point (mosfet gate), then the answer is usually 'yes, a capacitor is sensible'.

Working with the voltage divider resistor, the capacitor forms a RC low pass filter to smooth the bias voltage. Use an electrolytic.

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