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Old 2nd April 2012, 10:05 AM   #2321
sonnya is offline sonnya  Denmark
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I think the LM431/TL431 is used as a replacement for the Zeners???
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Old 2nd April 2012, 10:26 AM   #2322
Salas is offline Salas  Greece
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Yes those 15V ones that have a resistor on top as current feed. If the Vcc and current needed are hard to come by with a JFET CCS the 3.3K 2W can be retained for a higher rail amp like the BIGBT I guess.
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Old 2nd April 2012, 12:15 PM   #2323
hahfran is offline hahfran  Germany
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has anyone seriously considered why you'll never find those fancy cascode stuff in commercial amps priced below say 3000$?
and has anyone seen an audio IC that has such fancy stuff?
No?
Why not?
Its because of yield. Those cascodes may or even will require adjustment that means rework and that lowers the margin, in the case of IC the yield.
Its only worth consideration if the DIYer has plenty of time and enough equipment that could buy a 3000$ commercial amp combined.
You'll have to have plenty of prefessional know how to design a PCB such that those cascodes will not oscillate.
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Old 2nd April 2012, 01:26 PM   #2324
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Quote:
Originally Posted by keantoken View Post

The cascodes could easily be turned into Baxandall cascodes, rather than increasing Re, but this would probably not bring any technical benefits.


Youre very creative, with some experience youll make a very good designer, think the above part carefully through again.

Then try simming it.

Youll cure to a large extent another problem of the design as well as improve its performance by a couple oders of magnitude.

You can find such a design in a commercial product, its been 13 years I sold the design to them. Offcourse no input transistor cascodes though, that just messes some other parameters up. If youre going to use those cascodes be sure to place a cap across those small 10ohm resistors though.
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Old 2nd April 2012, 04:56 PM   #2325
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Originally Posted by MiiB View Post
It's not...Higher impedance M-Ohm would make it so...ideal CCS better option. difference is like bouncing a ball on a soft wooden floor and on solid concrete. One rattles the building and is felt everywhere. Both floors bounces the ball one just bounces the ball better..
No I didn't mean resistor should be at this spot, not at all, I said it is doing what can be expected from resistor nothing more. CCS were present in this spot before and were replaced with resistor because the simplicity. Not a good choice since distortions are way to high. As I said CCS wil be incorporated here. Will post some ideas about my solution regarding this.
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Old 2nd April 2012, 06:50 PM   #2326
Salas is offline Salas  Greece
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BJT cascode TO-126 CCS?
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Old 2nd April 2012, 07:14 PM   #2327
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Originally Posted by Salas View Post
Two LM329 a red LED and a BF245A G&S shorted topped with BF245C cascoding it, would beat TL431 with one hand tied at the back on high Z, noise, and PPM grounds. Provides power on indication too.
hehe yes obviously would be much better. First of all I had to replace two pin zener on PCB and put instead something small enough to fit in between neighbouring parts. Secondly TL431 were at my hand in my stock, so logical thing happened.

Replace a zener and current supply resistor with bunch of parts is not what is desired here. Our aim is always to make it in a simple manner, small parts count with perfect performance. I promise I will design new PCB, SSA BIGBT HP style to start GB when we'll perfect out complete schematic. At this moment I think we know a lot more how to improve SSA, give attention to its specific parts to improve its performance by a couple orders of magnitude, as homemodder said.

P.S. One important rule for combined zeners and CCS, they all have to be temperature independent.

Last edited by Lazy Cat; 2nd April 2012 at 07:27 PM.
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Old 2nd April 2012, 07:33 PM   #2328
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Originally Posted by hahfran View Post
You'll have to have plenty of prefessional know how to design a PCB such that those cascodes will not oscillate.
SSA BIGBT HP PCB is among perfect ones. No HF mistake, no mistake at all for given sch. We'll have to improve some parts of the sch for the next SSA PCB and I am willing to design it myself, no problem.
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Old 2nd April 2012, 08:00 PM   #2329
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Originally Posted by Salas View Post
BJT cascode TO-126 CCS?
TO-126 not needed here, we are talking about very high output impedance CCS supplying current from 15 V stabilized rail to input pair emitters, all together 0,12 W of power dissipation on one serial BJT (14,4 V voltage drop at 8 mA). Should be made out from app. three active parts plus few passives and completely temperature independent.
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Old 2nd April 2012, 08:05 PM   #2330
Salas is offline Salas  Greece
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I was thinking about substituting the main 3K3 2W feed in BIGBT. Now I understand you talk about those input pair 1K feeding branches I also substituted with BF245B CCSes one steady one variable in my bare bones 40W Latfet one. I saw 20% bandwidth expansion and better tempco for those.
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