Friday, September 4, 2020

Filter the noise out

 Examine this series of shots with the idea that the bypass is filtering certain frequencies. Pay attention to the generator frequency, generator Z and load Z.

From the series of shots you should be able to see some relationship between the generator Z and the bypass resistor value.

In order to function we would set R bypass less than Z gen. The filter is less effective when Z gen is 50 ohms.

Z bypass also needs to be less than Z load. Simply stated the bypass must be lower than the source and load.

You should be able to see a reaction to the input frequency.

That reaction is defined as 1 / ( 2 PI * F * C).

The calculated value for the cutoff or bypass frequency is 1.6Khz.
Final screen shot shows the response to 1600hz.
The last amp I built was very stable with the input shorted but would pick up strays when the input was open. Putting a low value resistor across the input helped but it would then load the tuner so a filter was called for. I used a simple L filter and it worked but this filter is used on LM386 amps so it could be a good alternate.

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