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b500 problem
b500 problem
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Old 28th May 2019, 02:49 AM   #11
nigelwright7557 is offline nigelwright7557  United Kingdom
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I have looked at the circuit for a good few minutes now and I cant see how it works, or at least not the op amp part.

With the input shorted the op amp rails will both be zero volts ! which means it is off.
If the input goes positive then the upper rail rises and turns on the next transistors along and driving the output stage positive.
If the input goes negative then the lower rail goes more negative and turns on the next transistor along and driving output stage negative.
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Old 28th May 2019, 02:58 AM   #12
karachay is offline karachay
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Originally Posted by nigelwright7557 View Post
If its intermittent first thing to do is do a good visual inspection for unsoldered or bad joints.
thank you my friend i will check again.
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Old 28th May 2019, 08:43 PM   #13
NMOS is offline NMOS  Germany
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Originally Posted by karachay View Post
hi friends i try make b500 from apex. i get alot of problems this amp steal my 3weekends i know its easy but i dont know why i still get problems. i finally make it work. but after 2 3 times close and open, one resistor get flame and burnd. when i check it i see my 5200 transistors get short too and fuse blow.

the resistor is R21 on schematic. 100R.

any idea why it can happen? it was working really nice and not getting hot
look pics transistor needs capacitor otherwise oscillation and amp selfdestruction

other pic professional amp very stable under heavy load
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File Type: jpg amp.jpg (220.5 KB, 52 views)
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Old 28th May 2019, 08:45 PM   #14
NMOS is offline NMOS  Germany
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600 - 1000 PF

about 500 - 600 PF and 1 uf for VBE
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Old 28th May 2019, 09:48 PM   #15
karachay is offline karachay
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600 - 1000 PF

about 500 - 600 PF and 1 uf for VBE
ty for your time and helping. i did write on my notes,

i use hammer and crash all 3 channels cause all people saying we did make it this amp. its not possible theirs working but my 3 channels not working. 1 channel qork abouth 1 hour and then it burn with flames.

some thing they change on circuit but they dont saying. this is only thing i can explane it. again thank you for answer have a nice day.
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Old 28th May 2019, 09:52 PM   #16
nigelwright7557 is offline nigelwright7557  United Kingdom
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Once you get it working again check the output for oscillation.
Oscillation kills output transistors.
As mentioned earlier the VAs needs feedback capacitors to slow it down.
I tend to use 100-220pf with good results.
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Old 28th May 2019, 11:35 PM   #17
NMOS is offline NMOS  Germany
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Originally Posted by karachay View Post
ty for your time and helping. i did write on my notes,

i use hammer and crash all 3 channels cause all people saying we did make it this amp. its not possible theirs working but my 3 channels not working. 1 channel qork abouth 1 hour and then it burn with flames.

some thing they change on circuit but they dont saying. this is only thing i can explane it. again thank you for answer have a nice day.
yes, thats true

class D same problem

are you sure no have fAKE devices in curcuit ?
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Old 28th May 2019, 11:45 PM   #18
NMOS is offline NMOS  Germany
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Quote:
Originally Posted by nigelwright7557 View Post
Once you get it working again check the output for oscillation.
Oscillation kills output transistors.
As mentioned earlier the VAs needs feedback capacitors to slow it down.
I tend to use 100-220pf with good results.
Yes, but better for safe stable working use 1000 - 1200 PF and 500 - 700 in VBE

was working 12 years in Club, other pic schematic subbass amps in club, never had problem with heavy overloading.

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