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Old 12th July 2011, 02:27 PM   #21
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Quote:
Originally Posted by dadod View Post
The cascode I suggested is actually proposed to me by Cordell in his book thread.

"I normally recommend caution in regard to the type of circuit you are using to bootstrap the input cascodes; I'm not crazy about injecting extra current into the LTP tail circuit. I might have used an emitter follower into whose emitter I would have flowed that current. I prefer the driven cascode that is driven by a replica of the feedback signal, which, under normal conditions, is pretty much the same as the common mode signal."

dado
Can't argue with "the man".

Done ! (below). Cascode reference is an in-phase replica of the feedback devices collector signal. This is my barn amps circuit now (and the original luxman's) , I just never knew the exact reason for this technique. One learns every day.

PS - LT shows a few PPM improvement over the other biasing techniques. My divider uses .5ma which can be offset with the adjustable CCS (another standard feature).

OS
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Last edited by ostripper; 12th July 2011 at 02:29 PM.
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Old 12th July 2011, 03:07 PM   #22
dadod is offline dadod  Croatia
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Quote:
Originally Posted by ostripper View Post
Can't argue with "the man".

Done ! (below). Cascode reference is an in-phase replica of the feedback devices collector signal. This is my barn amps circuit now (and the original luxman's) , I just never knew the exact reason for this technique. One learns every day.

PS - LT shows a few PPM improvement over the other biasing techniques. My divider uses .5ma which can be offset with the adjustable CCS (another standard feature).

OS
That exactly was my first circuit, but Cordell wrote this:

"I'm not crazy about injecting extra current into the LTP tail circuit. I might have used an emitter follower into whose emitter I would have flowed that current"

and I added emitter follower. Then Cordell suggested to chenge resistor with zener diode because as shown, it looks like there will be attenuation of the common-mode signal before it reaches the bases of the cascodes.
dado
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Old 12th July 2011, 06:05 PM   #23
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I will go for the zener (or the option of one) , but no more. The complexity vs. performance gains are minuscule. KISS - keep it simple , (stupid).
Thanks for the input, Dadod.
OS
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Old 12th July 2011, 08:40 PM   #24
dadod is offline dadod  Croatia
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Quote:
Originally Posted by ostripper View Post
I will go for the zener (or the option of one) , but no more. The complexity vs. performance gains are minuscule. KISS - keep it simple , (stupid).
Thanks for the input, Dadod.
OS
Everything should be made as simple as possible, but not simpler. ~Albert Einstein
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Old 13th July 2011, 08:00 AM   #25
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If R42 changes to zener, R43 should be CG, otherwise you have the same error (LTP current variations) like injecting new current into LTP (fixed cascode base).

Proper way in pic.
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Last edited by Lazy Cat; 13th July 2011 at 08:16 AM.
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Old 13th July 2011, 08:23 AM   #26
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Lazy Cat.
That is littlefishbicycle.com
and it is really a HIFI Power amp
A HiFi Power Amp
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Old 13th July 2011, 08:26 AM   #27
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I know and love its PCB layout.
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Old 13th July 2011, 01:39 PM   #28
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Default closer , just the IPS to go.

I actually just redesigned the whole thing (below 1) , wanted it to "look" SOTA. Is the choice of resistor OK ? (below 2) 10mm lead- spaced noble emitter resistors - non-inductive ?

Look at the 3 input stages (big attachment 3) , the sphinx , pioneer and luxman get away with the minimum. I am open to a "better" input stage , the input stage has more PCB real estate available than even the CCS/VAS , but let's keep it to some compromise that does not add semi's.

The below OEM's use primitive boosted supplies for the front end. Our PCB will have that as an option , but will default to a rather large 22R/470uf local decoupling scheme to power the input stage. Notice the 4 earth returns (2 for main decoupling , 1 each for vas/ccs and input ground). Notice the jumperless double sided layout that still has the option of jumpers if one want's to "etch their own". I'm sure the finished board will be so "golden" ,that only the "cheapskates" would do that ....

- deep into the input stage presently -
OS
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File Type: gif noble resistor.gif (134.9 KB, 2731 views)
File Type: gif input stages.gif (118.1 KB, 2753 views)
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Last edited by ostripper; 13th July 2011 at 01:46 PM.
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Old 13th July 2011, 01:57 PM   #29
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I like this jfet input stage: http://i.imgur.com/tjBOv.png based on a german made amplifier i have.

Those resistors are exactly what i use in my amplifiers.
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Old 13th July 2011, 03:04 PM   #30
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Originally Posted by Tekko View Post
I like this jfet input stage: http://i.imgur.com/tjBOv.png based on a german made amplifier i have.

Those resistors are exactly what i use in my amplifiers.
That is like the pioneer. It is real nice , BUT .... more sensitive to compensation (it tends to oscillate) if you don't get it EXACTLY right. Likes to (is more conducive) run a push-pull VAS. The pioneer only used the cascode as it did not have the reduced supply points like your German amp.

I would love to have suggestions on WHAT FET to use ?? , so I could physically
implement it (layout wise). Some are D-S-G vs. a BJT E-C-B , I need to know this to allow for BJT/FET interchangeability.
OS
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