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Old 12th September 2011, 05:41 PM   #1
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Join Date: Nov 2009
Location: Arges,Cutea De Arges
Default New amplifier problems

Hi. I recently started a project to build a stereo hi fi amplifier, but I came across some problems.One amplifier module burned and the other sounds weak about 25W at +-40V.I did not used all the original transistors 2sa872(2n5401) , MJE5731A TIP50(MJE15030-MJE15031) ,MJ15025 MJ15024(2SA1943 2Sc5200).
I want to fix the working module ,the schematic i used is the one below.
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File Type: jpg Crown pulse 300w.JPG (164.8 KB, 156 views)

Last edited by radu8982; 12th September 2011 at 05:43 PM.
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Old 12th September 2011, 06:13 PM   #2
jaycee is offline jaycee  United Kingdom
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Join Date: Apr 2004
Location: Norwich, UK
You cannot simply substitute transistors in this way. The circuit will be oscillating and the compensation will have to be re-designed to cope - assuming your substituted parts are suitable for the circuit.

Your big problem is that MJE15030/1 drivers and 2SA1943/2SC5200 outputs are a LOT faster than the original devices. The drivers are also used in a Sziklai configuration with the BF422/423 predrivers - this is also prone to oscillation unless correctly compensated.

Last edited by jaycee; 12th September 2011 at 06:17 PM.
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Old 13th September 2011, 06:32 AM   #3
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Join Date: Nov 2009
Location: Arges,Cutea De Arges
I would have used the original transistors but i can not find them in my country.I want to know how the schematic should look like with the transistors i am using.I also want to replace the BF423/BF422(below is a picture of how i got BF423) with 2N5401/2N5551 if it s posible and probaly 2sa1943/2sc5200 with 2STA2121/2STC5949.If the transistors are not appropriate please help me find some wich are.
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File Type: jpg BF-423-DSC04435.jpg (160.1 KB, 106 views)

Last edited by radu8982; 13th September 2011 at 06:44 AM.
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Old 13th September 2011, 06:39 AM   #4
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Join Date: Sep 2009
Location: Timisoara
Radu, you cannot expect people to be of any help when you did not use the parts that the designer recommended.
I also live in Romania at this time and i never buy electronic components from this country because most are fake. You can buy with confidence from Farnell or from Mouser.
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Old 22nd September 2011, 05:33 PM   #5
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Location: Arges,Cutea De Arges
With some help i got a working module and i want to now how to make it safe so i won't encounter problems.
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