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Old 6th March 2011, 10:26 AM   #351
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Quote:
Originally Posted by sudhir kumar View Post
hi apex,
I have made two module of this amp.First one made on wrong pcb design(post no.1) with correction done, is working fine but when i made second one on correct pcb design it is not working properly.I am using only 12-0-12 trafo for testing.When i am removing the diodes from the base of bc546,amp works.Voltage drop is also too much when comparing with first module. The positive side of amp is dropping the voltage too much while in first module there is no voltage dropping.MJE 340 getting hot.What may be the problem ? i have checked all the components and tracks for fault and short circuit but unable to find the problem .Is there any mistake with new pcb design ?Kindly suggest me
-regards.
sudhir
No mistake on new pcb, can you post pictures? Use trafo with higher voltage and 60-100W/220V bulb in series with primary for test.
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Old 6th March 2011, 11:21 AM   #352
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THis is not a good amp, even for beginners. For a start, there are no emitter resistors in the parallelled transistors (lower half). Many beginners would not know that they would have to match transistors accurately to even have some chance of evening out the power, and even then it is not a good idea to run without emitter resistors.
FOr another, 2N3773's originally (the RCA ones) had fT's of 200 kHz. Not good for audio. Modern ones MAY have fT's around 2 MHz but the data sheets generally say 200kHz still.
470 pF compensation capacitors will cause slew rate limiting at 4 MV/s - really poor. The best I can say is that this might match the slow speed of 2N3773's.
As for the output power and current, high current/voltage applications are not really beginners' projects. I'm not convinced that you could in fact obtain 550W from just four (x2) 2N3773's anyway. At least not driving difficult loads. Maybe just resistors.
Something like the Maplin 100W amp (two 2N3055/MJ2955 pairs) running from up to 40V is much more suitable. In fact that circuit was not so different, but the compensation capacitors were smaller (because the 2N3055 is faster).
ANd would beginners have 500W or more speaker capability?
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Old 6th March 2011, 02:22 PM   #353
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Quote:
Originally Posted by john_ellis View Post
apexaudio
THis is not a good amp, even for beginners. For a start, there are no emitter resistors in the parallelled transistors (lower half). Many beginners would not know that they would have to match transistors accurately to even have some chance of evening out the power, and even then it is not a good idea to run without emitter resistors.
FOr another, 2N3773's originally (the RCA ones) had fT's of 200 kHz. Not good for audio. Modern ones MAY have fT's around 2 MHz but the data sheets generally say 200kHz still.
470 pF compensation capacitors will cause slew rate limiting at 4 MV/s - really poor. The best I can say is that this might match the slow speed of 2N3773's.
As for the output power and current, high current/voltage applications are not really beginners' projects. I'm not convinced that you could in fact obtain 550W from just four (x2) 2N3773's anyway. At least not driving difficult loads. Maybe just resistors.
Something like the Maplin 100W amp (two 2N3055/MJ2955 pairs) running from up to 40V is much more suitable. In fact that circuit was not so different, but the compensation capacitors were smaller (because the 2N3055 is faster).
ANd would beginners have 500W or more speaker capability?
In real world this overcompensate circuit without any adjust is still valuable, look at the posts #182 and #243.
Any of my amp is good for beginners with single side pcb and without smd parts...
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Old 6th March 2011, 05:08 PM   #354
AndrewT is offline AndrewT  Scotland
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I agree with John and I said as much back in June last year.
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Old 9th March 2011, 03:55 AM   #355
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Quote:
Originally Posted by apexaudio View Post
No mistake on new pcb, can you post pictures? Use trafo with higher voltage and 60-100W/220V bulb in series with primary for test.
Regards
Now its working.I dont know what was the fault, i just changed the mje340/350(according to multimeter testing these are ok).i am attaching the pictures of both modules.one is made on reversed printed pcb.I have ordered for a 50-0-50 trafo & it will be used with 5pairs of o/p,20000uf cap per side.
just one question more...........is it a stable amp ? because i have read many critisism of this amp in this forum but i have selected this amp because of its simplicity & power.(offcourse i have a lot of 2n3773s too)
photo in next post.

Last edited by sudhir kumar; 9th March 2011 at 03:56 AM. Reason: attaching a photo
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Old 9th March 2011, 04:03 AM   #356
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quasi
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Old 9th March 2011, 06:16 AM   #357
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How big is the 50-0-50 ?

If it's big (800VA) it might have as good as 4% regulation, so if the line voltage does not rise at all you will have about 73V at idle. If the line rises you might have a problem.

http://www.antekinc.com/pdf/AN-8450.pdf

Can you select your devices for forward biased breakdown voltage?

I would buy an 800VA 45-0-45, the no-load voltage with 5% high line would be around 69V.

http://www.antekinc.com/pdf/AN-8445.pdf

The difference between 50V and 45V is less than 1dB.
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Last edited by djk; 9th March 2011 at 06:19 AM.
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Old 9th March 2011, 06:23 AM   #358
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to djk,
i am getting it manufactured from a local winder.According to my specification he will wind it for 50-0-50, 15amp.i will post the measurements after delivery.
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Old 9th March 2011, 06:53 AM   #359
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All transformers are rated at full load with nominal line voltage.

Have him wind it for 45-0-45 unless you can select transistors as I described.
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Old 9th March 2011, 08:39 AM   #360
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Quote:
Originally Posted by sudhir kumar View Post
Now its working.I dont know what was the fault, i just changed the mje340/350(according to multimeter testing these are ok).i am attaching the pictures of both modules.one is made on reversed printed pcb.I have ordered for a 50-0-50 trafo & it will be used with 5pairs of o/p,20000uf cap per side.
just one question more...........is it a stable amp ? because i have read many critisism of this amp in this forum but i have selected this amp because of its simplicity & power.(offcourse i have a lot of 2n3773s too)
photo in next post.
Amp is very stable, becouse it's overcompensate for working in class B without audiable distortion. Critisism is from people who are not diyers, just like teoretical discus about amps, and this is practical amp, clone of old DYNACORD, amp was usen for powered mixers and guitar amps.
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