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General Discussions => The Lab => Topic started by: lolo-m on January 10, 2009, 05:25:28 AM

Title: Fairchild's Time constants
Post by: lolo-m on January 10, 2009, 05:25:28 AM
On the PM670 pimp thread I've seen this :
(http://i52.photobucket.com/albums/g8/mobidik/660-time-constant.jpg)
1°)  Who can clealy explain to me how a simple RC (position 1 & 2) can have the same attack times with the same cap and different resistor values (  :o :o position 1: 220k//68k ; position 2: 220k//470K  :o :o ) ?
2°)  Who can clealy explain to me how a simple RC (position 1 & 2) can have different attack and release times ?
  ??? I'm really confused with this... ???
Title: Re: Fairchild's Time constants
Post by: gyraf on January 10, 2009, 07:52:24 AM
..attack time is determined by sc-transformer output drive impedance - so attack time depends on how much capacitance there is to drive, which is different for different release settings.

Jakob E.
Title: Re: Fairchild's Time constants
Post by: gary o on January 10, 2009, 07:54:25 AM
PRR he's the man........Intersting too clever for me but I bet PRR does know id be interested to read....thanks
 (Edit)While I was typing Jakob has sussed this one out ......cool thanks
Title: Re: Fairchild's Time constants
Post by: lolo-m on January 10, 2009, 08:26:24 AM
..attack time is determined by sc-transformer output drive impedance - so attack time depends on how much capacitance there is to drive, which is different for different release settings.

Jakob E.

Thanks Jakob .  ;)
Just to check if I understood well :
Attack time is given by the transformer current out charging the cap.
Release is given by the discharge of the cap through its parallel resistor.
Am I right ?
Title: Re: Fairchild's Time constants
Post by: nielsk on January 10, 2009, 08:52:23 AM
Un-related message attempt:
Gary, I have been trying to PM you with my email, but you inbox is still full!

Any chance of posting or hosting the whole schematic? This one looks much better than the one I the factory manual that I have....
Title: Re: Fairchild's Time constants
Post by: gyraf on January 11, 2009, 06:51:15 AM
Lolo - spot on.