Darius Loftin White explained - Page 9 - diyAudio
 Darius Loftin White explained
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 14th January 2009, 08:22 AM #81 diyAudio Member   Join Date: Mar 2008 @ #80 Hi Sheldon, yes, the output resistance is calculated in the following way: rout = RkKF II RS II riKF / (n x µ+1) rout ≈ riKF / (n x µ+1) rout ≈ 60KΩ / (0,5 x 101) rout ≈ 60KΩ / 50 rout ≈ 1K2Ω rKB = (riKB + µ x RkKB) rKB = (75KΩ + 100 x 1K5Ω) rKB = 225KΩ n = RaKB / (RaKB + rKB) n = 220KΩ / (220KΩ + 225KΩ) n ≈ 0,5 rout is the output resestance of the cathode follower RkKF is the cathode resistor of the cathode follower riKF is the internal resistance of the cathode follower triode, from data book ≈60KΩ riKB is the internal resistance of the cathode base triode, from data book ≈75KΩ rKB is the output resistance at the anode of the cathode base triode RkKB is the cathode resistor of the cathode base triode RaKB is the resistor between anode cathode base and bootstrap cap =220KΩ RS is the resistor from bootstrap cap to supply rail =220KΩ µ from data book ≈100 Kind regards, Darius
diyAudio Member

Join Date: Mar 2008
Quote:
 Originally #79 posted by kenpeter Does your 220K resistor present higher dynamic resistance to the ECC83's plate when so bootstrapped? ... If so, was that your main intention for this bootstrapping? Or you had some other important reasons in mind?
Hi kenpeter

The main intention was getting a factor >4 .
Putting two triodes in parallel is not possible because of the miller capacitance.
Influence of Cm at different volume settings

The bootstrap is a kind of "resistance multiplier"
ra = Ra / (1 - vu)

calculation of ra

Ra is the resistor between anode and bootstrap cap
ra = dynamic resistance to the triode's anode
vu is the gain of the cathode follower

comes from

Kind regards,
Darius

 14th January 2009, 04:44 PM #83 diyAudio Member   Join Date: Dec 2003 Location: San Diego Thanks for the calculation Darius. I'll have to draw that up and chew on it for a while. Nice to see you back here. Sheldon
 16th January 2009, 02:36 PM #84 diyAudio Member   Join Date: Mar 2008 @ #76 Hello, I uploaded the articles in an additional blog: link This blog is under construction. Kind regards, Darius
 19th January 2009, 10:15 PM #86 diyAudio Member   Join Date: Dec 2003 Location: San Diego I think you are trying to explain why this change is inferior to the original? Sheldon
diyAudio Member

Join Date: Mar 2008
#86

Quote:
 Originally #86 posted by Sheldon I think you are trying to explain why this change is inferior to the original? Sheldon
Hi Sheldon,
yes. In later applicationes Cgh is missing too. It is possible to make the hum compensation with C3 and C2 only. And this is the common method today e.g.
http://www.jogis-roehrenbude.de/Lese...Loesch-Amp.htm

#35 C4(=part three Loftin White C2) C5(=LWC3)

Kind regards,
Darius

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