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darlington/mosfet in emittor follower / headphone amp
darlington/mosfet in emittor follower / headphone amp
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Old 8th June 2005, 06:45 PM   #11
svokke is offline svokke  Belgium
diyAudio Member
Join Date: Apr 2003
Location: Leuven
lHow did you measure input impedance of transistor of 800 ohms?
This is very low, are you sure you did it correctly?
Maybe use a transistor of higher beta like 2sa4793
I measured the input resistance by putting a resistor between the base of the transistor and the opamp. Then measuring the voltage across the resistor. Then you have the base current. Then measure the voltage at the base. Base voltage divided by the base current= base input resistance.

The only difference compared to the first image, that I use resistors between the base and the emitter of the transistors. 4.7kohms for the BC, and 220ohms for the MJE.
Why is this done and how did you calculate the values?

I still have a lot to learn, that's one of my reasons why I like DIY
In illusion comfort lies
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Old 8th June 2005, 07:19 PM   #12
ilimzn is offline ilimzn  Croatia
diyAudio Member
Join Date: Feb 2005
Location: Zagreb
Default Re: Ilimzn

Originally posted by Gasho
G. ilimzn , vidim da ste iz Zagreba , pa me zanima možemo li nekako kontaktirati , barem preko maila?
Ilimzn_at_hotmail_dot_com ali rijetko provjeravam pa malo strpljenja. Alternativno, ilimzn na audiokarma.org - tamo je dopusteno slanje 'private messages'.

Sorry for hogging the thread folks, just a quick correspondence with a guy from where I live
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