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Old 20th December 2005, 10:54 AM   #1
YUTK is offline YUTK  Thailand
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Default Reduce input noise

How I can reduce input noise at input stage ,How many solution to fix it
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Old 20th December 2005, 11:03 AM   #2
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signal capacitor(no electrolytic,m/f or poly cap recomended)
100k resistance to gnd(m/f recommended)

see image.

Sagar
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Old 20th December 2005, 11:23 AM   #3
murphy is online now murphy  Germany
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Default Solution: Low Input Resistance

Reduce the input resistance of your circuit. So vou reduce the voltage noise ! If possible, it ist he best solution at lowest cost.
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Old 20th December 2005, 12:19 PM   #4
lineup is offline lineup  Sweden
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Hello

Put one 1nF capacitor
from input transistor base
to input ground
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Old 21st December 2005, 03:34 PM   #5
K-amps is offline K-amps  United States
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Quote:
Originally posted by lineup
Hello

Put one 1nF capacitor
from input transistor base
to input ground

That would reduce the HF extension wouldnt it? i.e. roll it off.
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Old 21st December 2005, 05:25 PM   #6
lineup is offline lineup  Sweden
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Quote:
Originally posted by K-amps

That would reduce the HF extension wouldnt it? i.e. roll it off.
Yes, it is a lowpass filter, for high freq. Say like above 500 kHz.
The size of this cap depends on how much resitance from source output.
It is a simple RC filter.
Most every serious amplifier design use this little cap
to input ground.

Sometimes, if not using this cap,
amplifier input can act as a radio receiver and we can hear radio programs!
The components before input, if not shielded,
act as an radio antenna.
Even if we can not hear anything, the HF-noise will disturb
the amplifier operation.
Increase distortion within circuit.
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Old 21st December 2005, 05:44 PM   #7
K-amps is offline K-amps  United States
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SO what kind of noise can be reduced by the 1nf...Audible Hiss? radio programs?

thanks.
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Old 21st December 2005, 06:05 PM   #8
lineup is offline lineup  Sweden
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Quote:
Originally posted by K-amps
SO what kind of noise can be reduced by the 1nf...Audible Hiss? radio programs?

thanks.
Anything that enters a sensitive input stage will effect the circuit.
There is no musical information above 500 kHz.
There is nothing lost by blocking HF-noise.

We are surrounded by a constant HF-noise. A background noise.
It is a mixture of many different frequencies.
We can not hear it
, by our mobile telephones and radio recievers
can filter out some information and transform it into data and sound
that a human can hear and understand.

For a sound signal amplifier this noise have no value.
So we filter away this BEFORE it enters amp.
It can only disturb, upset circuit opration.

I do not know if I can explain this more clearly.
I am sure there is more on the web on this subject.
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Old 21st December 2005, 06:30 PM   #9
K-amps is offline K-amps  United States
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Spare a thought for the bats that enjoy a good track or two...

By the way, from what I hear, the effects of phase shifts caused by rolling off HF at inaudible frequencies can themselves be audible. Now having said that I do not know if 500kHz roll off would have any appreciable phase shift, hence my prodding you for info.

thanks again.
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Old 21st December 2005, 06:40 PM   #10
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Wouldn't it be a better option to treat the source component that's producing the noise?
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