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Old 29th November 2008, 10:28 AM   #1
Stee is offline Stee  Italy
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Default SuperOPA

this is just a project for 50W class A
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Old 29th November 2008, 11:54 AM   #2
Nrik is offline Nrik  Denmark
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Nice topolgi.

Drivers and outputs are BJT's but shown as FETs.

You forgot the feedback.

1 ohm is a pretty high value for emitter resistors in a 50W class A amp. (Edit: and I see now they are in the collectors - is that the way to do it?)

Are the tempco of the 33ohm NTC suitable to fit the outputs BJTs PTC?

But Stee - keep on going.
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Old 29th November 2008, 12:33 PM   #3
Stee is offline Stee  Italy
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Default Superopa2

see now

0R47 with 1,5A of final's Ice current

need a big silent fan on dissipator

feedback
RA and RB can have ratio of 1:15
RA = 560
RB = 8K2
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Old 30th November 2008, 08:08 AM   #4
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Haven't you drawn the output transistors the wrong way. I guess they should be common collector, not common emitter, or am I missing something?
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Old 30th November 2008, 09:08 AM   #5
Stee is offline Stee  Italy
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Default yes you are right

i have taked inspiration from Accurphase design
so in the original schematic
the output bipolar was in reversal mode

but my idea is use output resistor as negative feedback
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Old 30th November 2008, 09:16 AM   #6
Stee is offline Stee  Italy
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Default see the original

directly from japan
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Old 30th November 2008, 10:12 AM   #7
Nrik is offline Nrik  Denmark
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Are you copying the Jung buffer input of that circuit or are you coying the darlington commomemitter driverstage?

It looks more like a Sziklai, and in that case I am not sure you can put the drivers emitters on the opposite outputs collector.

If you simulated it or build it and it works, then I am just gonna say - super - tell us how it sounds.
Otherwise check the sziklai from other amps, and see how they do.
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Old 30th November 2008, 01:34 PM   #8
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Default Re: see the original

Quote:
Originally posted by Stee
directly from japan
Since the whole schematic can't be seen, we don't really know what happens outside this fragment. It's not a Sziklai.

Look at the direction of the transistors to the left in this schematic. I think this is how it should be.
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Old 30th November 2008, 02:33 PM   #9
Stee is offline Stee  Italy
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Default It's not a Sziklai

it's a Stee's invention!
next WE I will try to build...
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Old 30th November 2008, 04:15 PM   #10
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Default Re: yes you are right

Quote:
Originally posted by Stee
i have taked inspiration from Accurphase design
so in the original schematic
the output bipolar was in reversal mode

but my idea is use output resistor as negative feedback

This output is drawn as positive feedback, the more V across the .47 Ohm resistors the harder the output is driven. Magic smoke?
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