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Old 10th October 2009, 07:14 PM   #171
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Another question, showing up my bad knowledge:

I would understand a SRPP with only a single resistor made. But here the output is taken between 2 resrstors. Why???? I also have another question concerning the 6-critter: Why don't we use a few resistors and a capacitor to form the voltage source???

Thanks, Dirk
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Old 10th October 2009, 10:41 PM   #172
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This would not be considered SRPP, which is generally
shown with 1 resistor. The mu follower is the one generally
shown with two resistors, although they are simply
gain variations of each other.
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Old 11th October 2009, 09:20 AM   #173
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Hi Nelson,

the mu-follower works for me like that: Use the first resistor to create the bias. Use a second (larger!) resistor to create the drive. Couple the drive with a capacitor to the gate.

I can't see similarities to your circuit.

Dirk
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Old 11th October 2009, 09:58 AM   #174
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Quote:
Originally Posted by HVfanatic View Post
Hi Nelson,

the mu-follower works for me like that: Use the first resistor to create the bias. Use a second (larger!) resistor to create the drive. Couple the drive with a capacitor to the gate.

I can't see similarities to your circuit.

Dirk
imagine that second resistor made from two resistors .
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Old 11th October 2009, 10:10 AM   #175
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Hi ZenMod,

but why do we tap the signal in between the resistors???

Dirk

And: the voltage source must not be coupled hard between gate/source, otherwiese the Resistors could not modulate the Jfet - right???
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Old 11th October 2009, 04:55 PM   #176
JimT is offline JimT  Canada
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I don't know the circuit that Nelson has designed, but optimizing the SRPP to it's load may be the reason for using two resistors here. See the recent series of articles by John Broskie on http://www.tubecad.com/ .

Jim
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Old 11th October 2009, 06:38 PM   #177
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by HVfanatic View Post
Hi ZenMod,

but why do we tap the signal in between the resistors???

Dirk

And: the voltage source must not be coupled hard between gate/source, otherwiese the Resistors could not modulate the Jfet - right???
Quote:
Originally Posted by JimT View Post
I don't know the circuit that Nelson has designed, but optimizing the SRPP to it's load may be the reason for using two resistors here. See the recent series of articles by John Broskie on http://www.tubecad.com/ .

Jim
well ..... first thing is that I don't have SS 3-legged fuses near (enough to) me , and second ( pretty more important) thing is that I'm certainly not Papawakoo enough to know many things .......

anyway - imagine that lower part of amp - made of input Jfet+lower output Jfet have some ..... ok - xconductance (maybe better word is transfer function );

probably upper part of amp - comprised of upper output Jfet have another xconductance (transfer function ) ;

these two resistors are (probably) there to make these two transfer functions "same" , to make funny SRPP output halves to working in unison ;
symmetrical clipping ..... blah blah .....

anyway - my crystal ball is lately pretty muddy , and usually all I can see is my lack of official education in field of electronic ; not to mention evident lack of talent ......

so - this is how little ZM imagine how white puff works inside these critters ...

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Old 11th October 2009, 09:37 PM   #178
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This is pretty elementary stuff. Meditate on it, and you
will experience the "aha!".

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Old 11th October 2009, 09:57 PM   #179
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Assembly of Japanese bicycle require great peace of mind
aha !

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Old 12th October 2009, 06:30 AM   #180
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Though my knowledge in electronics is rather limited – I do not understand the mu follower or SRPP subtleties - I think I got the mainlines of how the J2 works.

Let-s call R1 and R2 the upper and lower resistors.
Imagine the bottom leg of the voltage source has moved to R1/ R2 middle point.
The upper jfet is oubviously a current source, the lower one a single ended amplifier.
That is like a Zen output.
Here we have to remember how current varies into the two output devices when a signal is applied to such an amp.
The upper device ( and so does R1) see a constant current.
The current into the lower device varies following the current into the load. From nearly zero when the device is quite “off” to 2 x Bias current when the same device is quite “on”
So, if the voltage across R1 remains constant, the voltage across R2 is an image of the output current.
Moving the lower leg of the voltage source to the other side of R2 makes the output current modulate the current source. Such as an Aleph one.
...But may be I am wrong.
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