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Old 2nd March 2012, 09:35 AM   #2031
PauloPT is online now PauloPT  Portugal
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What's the optimum bias across drivers and laterals?

Those of you who built it (the lateral fets version) how does it sound?
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Last edited by PauloPT; 2nd March 2012 at 09:44 AM.
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Old 2nd March 2012, 09:53 AM   #2032
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Look a bit back, bias has been discussed. Short answer, 150-200mA. For some comments look early in the thread, Nico was talking a bit 'bout his version you contemplate.
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Old 2nd March 2012, 10:07 AM   #2033
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I'll do

Thanks!
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Old 2nd March 2012, 11:02 AM   #2034
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Quote:
Try R6,8,11,12=510 Ohm
Quote:
Also R13,16,23=375 Ohm for ~3mA bias in the drivers and ~100mA in the Lats.
So for 180mA bias what would be the value of this resistors?
Forgive my poor knowledge of electronics design, I'm reading Sedra & Smith - Microelectronic Circuits - for learning but I'm still very in the begining.
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Old 2nd March 2012, 11:16 AM   #2035
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Run .op and manipulate R23 until you will get what you need through the LATs. In reality R23 better be a trimmer. The simulator won't have exactly the same Vbe for the drivers or Vgs for the LATs as each one ranging practical part. Just make Nico's as given but with trimmer R23, trimmer R6 and see if it will bias up and work stable on you. You gotta get hands on to experience how it moves... In mysterious ways that is.
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Old 2nd March 2012, 12:36 PM   #2036
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Quote:
Just make Nico's as given but with trimmer R23, trimmer R6 and see if it will bias up and work stable on you.
With Nico's values for the resistors distortion is huge. The sugested above values work like a charm! Why did Nico used the values that give worst distortion?
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Old 2nd March 2012, 02:30 PM   #2037
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One more thing: could I use 2SK1530/2SJ201 instead of 2SK1058/2SJ162 ?
They are not lateral but close.
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Old 2nd March 2012, 02:48 PM   #2038
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Only laterals. What Nico showed are real values biasing real parts. Those which worked best in LT Spice are biasing models. Shows how sensitive it is non the less, because those values I gave for the good sim aren't really far. You got to see when hands on and use trimmers on crucial ones until you set it right as I said. Those are just my general opinions trying to help out though, I am not Nico and maybe the right answers are different, remember. In general this is a practical thing. You make it, you evaluate bias and stability on your layout, you try for good offset. You gotta have generator and scope absolutely. Not recommended as novice's project. If in doubt, get official boards and make F5, next of kin best thing. Just my plan B suggestion if things go wrong, not trying to disappoint you.
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Old 2nd March 2012, 03:24 PM   #2039
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not trying to disappoint you.
You're not disappointing me, I thank you for your advice.
This is an interesting thread. I'll be following it and when a final stable design is achieved I'll build it.

Thanks.
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Old 2nd March 2012, 04:41 PM   #2040
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Hi PaulPT,

There is no absolute GO/NO-GO condition in analogue electronics and tweaking practically is more often than not the final stage of the design. Besides, I think that DIY audio guys (myself included) places far too much emphasis on harmonic plots from simulators.

It is possible to optimise every component using a simulator and get really silly numbers. Problem is one eventually believes that it will be the actual performance of the product - it never is.

I am still using my lazy cat to this day, everyday in my office. Even with the assumed high level of simulated distortion, its sound remains absolutely magic.
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