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Re: Hawksford current source?

I found the idea for a Hawksford CCS here on this audioasylum, it consist of adding a capacitor from the lower transistor's base to the upper's emitter.
Voltsecond has a webpage with it at:
http://www.siteswithstyle.com/VoltSecond/c4s_cascading_in_psu/C4S_cascading_in_psu.html
It's also known as a bootstrapped CCS from Kurt Strain.
http://db.AudioAsylum.com/cgi/m.pl?forum=tubediy&n=13763

I did a simulation in B2 Spice with the different versions and here's their impedance:
-CCS with one BF872: 1.7 Meg
-CCS with two BF872 in cascode: 3.6 Meg
-CCS with two BF872 in Hawksford or bootstrapped cascode: 60.0 Meg

Regards,

Danny


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