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Old 23rd November 2010, 03:47 PM   #31
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That is correct, but double check your offset to be sure it is close to minimum.

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Old 23rd November 2010, 04:07 PM   #32
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Old 23rd November 2010, 04:30 PM   #33
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Generg - I'm not sure now what was a call regarding value of R14 ;

Bill told you just to check voltage across it - to determine current through left side of LTP and compare is it 50% of overall LTP current

value of R14 is dependable of needed (Ugs+Urs) for desired output Iq and don't have anything with proper current share in LTP itself

varying LTP current and R14 value will vary OLG and feedback ........ but that's another part of story
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Old 23rd November 2010, 04:54 PM   #34
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hm, hm....

you both know to much for me to discuss your thoughts, but I can do what you suggest and hear the sound and get more feeling for theory reading your comments .....

I will try different values in the range opened by the discussion and given by Nelson.

In A3 the current through the differential pair is also around 20mA ....if I read the SM correct, in A3 and A5 the values he suggested are 750 and 450 Ohm.

next days I will measure with a 60Hz tone the voltages Nelson described in Zen Variations 2, just for fun, learning something new....and never giving up....
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Last edited by generg; 23rd November 2010 at 04:56 PM.
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Old 23rd November 2010, 05:16 PM   #35
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Originally Posted by Zen Mod View Post
Generg - I'm not sure now what was a call regarding value of R14 ;

Bill told you just to check voltage across it - to determine current through left side of LTP and compare is it 50% of overall LTP current

value of R14 is dependable of needed (Ugs+Urs) for desired output Iq and don't have anything with proper current share in LTP itself

varying LTP current and R14 value will vary OLG and feedback ........ but that's another part of story
I believe there is a slight language barrier. Please read my post again. I have taken into account all the points that you mention. The Vgs of the R100s determines the voltage needed across R14. If the offset is minimal then it is in the correct range, and then the voltage drop divided by the proper current determine the proper resistance. If the amp is operating with high offset, the voltage range for the R100s will be incorrect and will throw the current sharing off in the front end.
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Old 23rd November 2010, 05:23 PM   #36
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there is sometimes just too much for typing .......

NB that 5mA per input jfet is good

also - 10mA - as in FW J2 is good for driving one output gate

two input Jfets have x transconductance

that combining with y value of needed drain resistor at 10mA of current will give exactly Ugs+Urs for Iq of ~1A5 to 2A ...... and that will give z OLG , which - combining with feedback net set at 10x will give xx db- of feedback , giving yy output impedance ...........

rise time , blahblah ......

so - conclusion - whatever stage you think of ......... just let it bleed
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Old 23rd November 2010, 05:28 PM   #37
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Quote:
Originally Posted by Bill Fuss View Post
I believe there is a slight language barrier......
there are 3 of us here , in this moment .....

I wasn't sure that Generg is following you - at least in moment when he started to write resistor values , instead of currents/voltages through LTP and each half of it

so - I think that I know what you were saying ....... but wasn't sure what Generg is measuring

one more thing - Generg - voltage accross drain resistor in input LTP seems little off - decreased at least for value across output Jfet source resistor ?
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Old 23rd November 2010, 05:31 PM   #38
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This ain't rocket science. I think Generg gets it. If he works through a couple of NPs previous Aleph front ends he will get it.

Last edited by Bill Fuss; 23rd November 2010 at 05:34 PM.
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Old 23rd November 2010, 05:37 PM   #39
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Quote:
Originally Posted by Bill Fuss View Post
This ain't rocket science. .........
yup

Quote:
Originally Posted by Bill Fuss View Post
..... I think Generg gets it. If he works through a couple of NPs previous Aleph front ends he will get it.
for sure ; Generg is ..... Generg !

seems that little confusion started in multilateral chat
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Old 23rd November 2010, 06:03 PM   #40
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Hi Zen Mod,


Quote:
one more thing - Generg - voltage accross drain resistor in input LTP seems little off - decreased at least for value across output Jfet source resistor ?
measured 1,9V across drain resistor input LTP and 0,5V over source resitor of SS is 1,4V, not a good value for Vgsthreshold?
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