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Old 19th March 2006, 02:19 PM   #1
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Smile balanced line stage

Hi all, i have done the balanced line stage preamp but i have some problems with the power supply.
Probably the negative branch has an autoscillation.
Are there modifications or suggestions to solve the problems?

Thanks
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Old 20th March 2006, 05:08 PM   #2
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Alessandro,

?? Probably the negative branch has an autoscillation

Use little caps to avoid this: 2* 0.1 microF 100volts plus 2* 100 microF 100volts
at bouth ends of the negative cable should do the trick.

A little picture of your design could help.

Regards.

Alain.
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Old 26th March 2006, 10:42 PM   #3
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I have already tried this suggestions but the problem remain.
The positive branch go very well but the negative roasted all the zener and the mosfet after 2 second.
Is it possible that any one had the same problem ?
Only another question, i have used 0,5 watt zener, maybe this is the problem ?

thanks

PS
i have used the original PCB designed by Nelson Pass
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Old 27th March 2006, 12:07 AM   #4
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Alessandro,

Did you check the 4.75 K R102 as for 16 Volts its about 4 milli Amps
so the 4.75 K is the problem
{4*4 milli * 9.1 volts == 0.1 milli watt for each zener even 1/4 watters
will be good} or Z116 is reversed. Or the mosfet short.
I did build this negative PS twice without any pb.

Alain.
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Old 27th March 2006, 05:38 PM   #5
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Default Re: balanced line stage

Quote:
Originally posted by Alessandro
Probably the negative branch has an autoscillation.
What symptom makes you think that?
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Old 30th March 2006, 01:14 PM   #6
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Hi all, i have solved the problem.
It was the 221 resistor on the gate.
i have tested it, and moving this on the board, the component change its value if i push on the body.

I have substitute the component and now all it's OK.
After 20 years of electronics job this is the first time that i have found this type of problem.
We don't never finished to learn......

Thanks at all for the help
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