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Old 20th January 2011, 10:31 AM   #11
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Originally Posted by Yarpen View Post
This is the schematic with your comments and PCB design
wow!
nice star gnd and power tracks
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Old 20th January 2011, 01:18 PM   #12
Yarpen is offline Yarpen  Poland
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I added a voltage regulators ( LM series 18V ) with the filtering and decoupling capacitors.
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File Type: pdf schematic.pdf (16.2 KB, 28 views)
File Type: pdf PCB.pdf (32.3 KB, 16 views)
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Old 20th January 2011, 02:00 PM   #13
Yarpen is offline Yarpen  Poland
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Schematic with voltage regulators
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File Type: pdf schematic.pdf (16.2 KB, 24 views)
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Old 20th January 2011, 02:20 PM   #14
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I'd move the bias pot to between B and E of the bias transistor.

As you have it now, the amp will go into self destruct if the wiper looses contact.
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Old 20th January 2011, 02:55 PM   #15
Yarpen is offline Yarpen  Poland
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Done
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File Type: pdf PCB.pdf (32.9 KB, 22 views)
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Old 20th January 2011, 03:29 PM   #16
Bigun is offline Bigun  Canada
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Again, without any gnf the PSRR will be relatively low. The regulators will help with the OpAmp if done well but the bias of the output devices feeds directly off the rails - perhaps these bias points should be moved so that they connect to the power rails after the RC filters.

You'll find it handy to have a probe point or connector for measuring the voltage between the emitters of the output devices - to check on the bias current.
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Old 20th January 2011, 04:07 PM   #17
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Originally Posted by padamiecki View Post
this would kill the benefits of the sound quality
do not apply gnfb
So you think more crossover distortion is good for sound quality? Using an opamp means the circuit already uses a lot of feedback (and its global except for the output), including the output in the loop will make it sound worse how? Or are you just regurgitating the no GNFB mantra?
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Old 20th January 2011, 04:16 PM   #18
cbdb is offline cbdb  Canada
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Again, without any gnf the PSRR will be relatively low.
As well as a higher output impedance. The catch might be stability.
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Old 20th January 2011, 07:09 PM   #19
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Again, without any gnf the PSRR will be relatively low. The regulators will help with the OpAmp if done well but the bias of the output devices feeds directly off the rails - perhaps these bias points should be moved so that they connect to the power rails after the RC filters.

You'll find it handy to have a probe point or connector for measuring the voltage between the emitters of the output devices - to check on the bias current.


Does replacing resistors R3 R10( from last schematic ) by current sources solve the problem?
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Old 20th January 2011, 08:31 PM   #20
Bigun is offline Bigun  Canada
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It would certainly improve the PSRR but why not simply include the bias inside the RC filtered part of the power supply ?

You could also bootstrap these resistors from the output, this would also improved PSRR and provide a more constant current through the bias string. You just replace R3 with two resistors and tie a capacitor from their mid point to the output.
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