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Old 22nd April 2013, 12:53 PM   #1
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Default ECC88 mu-follower

Hey guys, I need to know the output impedance of the attached schematic.

TIA
Felipe
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Old 22nd April 2013, 01:01 PM   #2
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Hi!

Sometimes a little googling helps and you find pages like these:

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Thomas
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Old 22nd April 2013, 01:42 PM   #3
DF96 is offline DF96  England
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I would not trust the calculations on that site. He doesn't seem to have understood how SRPP actually works.

For some understanding try Merlin Blencowe's site - the valve wizard.
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Old 22nd April 2013, 02:10 PM   #4
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Plese who knows the output impedance?
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Old 22nd April 2013, 02:16 PM   #5
DF96 is offline DF96  England
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The original designer?

To calculate the output impedance you need to know the valve operating point so you can find the mu and ra. Then plug these into the formula which Merlin gives on his site.

Then remember that output impedance and optimum load impedance are not the same thing so be clear what you actually want to know.
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Old 22nd April 2013, 02:32 PM   #6
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Hi!

Or just build it and measure it. Should be a quick job to breadboard such a circuit

Thomas
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Old 22nd April 2013, 02:33 PM   #7
euro21 is offline euro21  Hungary
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LTSpice sim: about 400R (at 1kHz)

Last edited by euro21; 22nd April 2013 at 02:37 PM.
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Old 22nd April 2013, 02:39 PM   #8
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Quote:
Originally Posted by euro21 View Post
LTSpice sim: about 400R (at 1kHz)
Thank you, Thomas link: platten spieler calculator sim about 321 ohms, can be good for 300 ohms load?
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Old 22nd April 2013, 02:45 PM   #9
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Quote:
Originally Posted by merlin el mago View Post
Thank you, Thomas link: platten spieler calculator sim about 321 ohms, can be good for 300 ohms load?
No, output impedance is no indicator of drive capability. As a rule the load should be no less than 10 times the output impedance.


Cheers

Ian
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Old 22nd April 2013, 02:47 PM   #10
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You are welcome Ian, how can change something of schematics posted in the 1st post to increase drive capability for 300 ohms load?
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