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Old 7th April 2014, 06:45 AM   #11
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As I mention R100 is different from IRFP240 which used in Aleph 3, 30 then how do I control vgs of R100, R125 ?
Only trim pot ?
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Old 7th April 2014, 06:55 AM   #12
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read this :

The Aleph Jango
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Old 8th April 2014, 09:52 AM   #13
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This's what my idea.
Combination of Aleph and Jfet Mu Stage, M-MU-J or M.u.J

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Old 8th April 2014, 09:59 AM   #14
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feel free to experiment

you have finished recipe for Mu with IRFP - in ACA schematic

besides that - if you have values and sch of J2 , be aware of fact that Pa didn't published that schematic
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Old 8th April 2014, 10:11 AM   #15
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Quote:
Originally Posted by Zen Mod View Post
feel free to experiment

you have finished recipe for Mu with IRFP - in ACA schematic

besides that - if you have values and sch of J2 , be aware of fact that Pa didn't published that schematic
Yeah...I have only output section, non publication for all.
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Old 10th April 2014, 05:11 AM   #16
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I found something wrong with my trimpot. It should be liwer than 500 Ohms because R100/125 need vgs 1.2V across thus trimpot and IRF9610 need bias current 12mA/ea then trimpot must be around 100-200 Ohms for 1.2V/100Ohms=12mA
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Old 11th April 2014, 01:30 AM   #17
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yes that sounds about right - although i think you would be best placed keeping the drain resistor load as a fixed value (say 200 ohms or so) and then adjusting the CCS set resistor R11 in your schematic. You 'loose' less gain by adjusting current for a given Vgs vs adjusting the drain resistor and keeping the current constant.

Also the macmillan resistors are neat but maybe for test and development purposes you can just use a low value trimpot between the source of the LTP fets for offset adj purposes (which is what those resistors are meant to achieve)

As regards the choice of the input mosfet, there are other devices you can try nowadays - some alas not easy to find (SJ313) and others still available (IRF9Z24). You'll find that these devices have their own 'sweet spot' (combination of drain resistor and bias current) and so may be better suited for the job of driving the jfet op devices. Only way to find out which is best is (imho) through plenty of experimentation.

Good luck mate!
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Old 11th April 2014, 06:42 AM   #18
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I'm not seeing McMilan resistor there

as I recollect , those are sort of support for Tail node of LTP, acting as Terra Firma , so demanding two opposite originating nodes .... usually found as balanced outputs
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Old 11th April 2014, 09:37 AM   #19
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Thanks ZM - mea culpa!
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Old 11th April 2014, 09:48 AM   #20
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Algar_Emi's file , always handy to us Greenhorns

Attached Files
File Type: pdf Aleph30by Algar_emi.pdf (29.9 KB, 24 views)
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