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If the mic and pot are connected with ordinary wires then they are antennas that pickup hum.
Shielded audio cable MUST be used.
The lowpass filter is designed to cut 973Hz a little but gradually reduce higher frequencies and still produce 9700Hz.
The lowpass filter is not a filter if it feeds a normal low impedance mic input on an amplifier.
IF the amplifier has a very high input impedance of 2M or more (but a mic input might be only a few thousand ohms) then you can use a 100k series resistor then a 2nF capacitor ground to cut all mid and high frequencies above 800Hz.
But a normal low impedance mic input will attenuate the signal level to almost nothing.
You said the mic is 25 ohms. Then to cut all frequencies above 800Hz, connect a 8uF capacitor parallel with the mic.
Why do you want to cut all mid and high frequencies? Then speech will be only vowels, AY, EE, EYE, O, and OO.
IF the amplifier has a very high input impedance of 2M or more (but a mic input might be only a few thousand ohms) then you can use a 100k series resistor then a 2nF capacitor ground to cut all mid and high frequencies above 800Hz.
But a normal low impedance mic input will attenuate the signal level to almost nothing.
You said the mic is 25 ohms. Then to cut all frequencies above 800Hz, connect a 8uF capacitor parallel with the mic.
Why do you want to cut all mid and high frequencies? Then speech will be only vowels, AY, EE, EYE, O, and OO.
A resistor in series then a capacitor to ground is a lowpass filter that can feed an amplifier that has a very high input impedance. If the resistor is 100k ohms and the amplifier input impedance is 5k ohms (a normal mic input) then the output level at low passing frequencies is reduced 1/21 times.
The 10k input resistance of the amplifier loads down the signal level to near nothing.
The mic already has a fairly low resistance of 25 ohms and can feed a 5k amplifier input resistance with almost no signal level loss. Then filter the mic with a capacitor in parallel with the mic like I said in your other thread about it.
If an amplifier has a microphone input it probably has an input resistance of 5k ohms for a dynamic (coil and magnet) mic. It has a very high gain.
A an electric guitar input input has a resistance of a few million ohms and not much gain.
Aren't you connecting your mic to a mic input?
Oh, sorry.You can use any shielded cable you want. I am talking about which input on an amplifier, not which cable.
Usually a mic is plugged into the mic input on an amplifier.
The output level of a mic is about 0.01V feeding about 5000 ohms. The electric guitar input on an amplifier is about 1V at 3 million ohms. A huge difference of signal level and resistance.
Hi,
The circuit for the pots is obviously wrong.
What is your idea? How should they work? What should they do?
Klaus
Hi Daniel! I haven't try it, but I should give it a try! I'll let you know what the results are. Thank you!Hi,
I'm not sure if this has already been suggested as a solution to the problem described in post #1 regarding the humming when turning the trimpot from 0 to 10 or viceversa, I'm a bit lost in this thread by now, interesting as it is. Out of curiosity, have you tried a 55HZ or a 100Hz band-reject filter across that potentiometer and turned the potentiometer from 0 to 10 and back again to see if it does anything to get rid of the noise/hum. Probably won't work, and it would attenuate any signal of interest at the same time, but just to see if the noise/hum goes away at all.
I did a simulation for 55Hz. You could use 1k and 1.47uF for around 100Hz.
I used this calculator called Band Stop Filter Calculator for the original values, the simulation begged to differ a little about RC values needed, normal. While not a great representation of your actual set-up, at least it's helpful to see what the band-stop should do.
View attachment 165212
I don´t know what your idea is. That´s why I asked for it. I still don´t know - or not understand.but why is the idea wrong?
Hi,
obvious...
* they are not related to the filter
* both pots are in parallel
* they just act as a variable ohmic load to the input signal.
and if the wiper is at one side, it will short circuit any input signal. (at least for the simulation, but not for a real pot)
For sure there will be no hum anymore.
And you have the simulation tool. So use it.
--> Does the pot position make any difference from 1% to 100%?. I doubt it.
I don´t know what your idea is. That´s why I asked for it. I still don´t know - or not understand.
Klaus
You know there is no capacitor involved in the pot circuit that can act as low pass filter ?the idea first was to put a 100k potentiometer with a capacitor to act as a lowpass filter
With the pot lower_end connected to the star point and nowhere else? I still don´t see this in your circuits.The main problem was that when I turned the pot down to "0" it started to hum.
I don´t see this. What schematic are you talking about?I put a 100 ohm resistor in series (I couldn't find a potentiometer with that low value) and a 2nF capacitor to ground and it worked out!
Your filter reduces 53Hz only -3dB which is barely noticeable. Besides, a video of the hum makes it sound like a 100Hz triangle waveform that has many harmonics.Hi,
I'm not sure if this has already been suggested as a solution to the problem described in post #1 regarding the humming when turning the trimpot from 0 to 10 or viceversa, I'm a bit lost in this thread by now, interesting as it is. Out of curiosity, have you tried a 55HZ or a 100Hz band-reject filter across that potentiometer and turned the potentiometer from 0 to 10 and back again to see if it does anything to get rid of the noise/hum. Probably won't work, and it would attenuate any signal of interest at the same time, but just to see if the noise/hum goes away at all.
I did a simulation for 55Hz. You could use 1k and 1.47uF for around 100Hz.
I used this calculator called Band Stop Filter Calculator for the original values, the simulation begged to differ a little about RC values needed, normal. While not a great representation of your actual set-up, at least it's helpful to see what the band-stop should do.
View attachment 165212
Hi,
You know there is no capacitor involved in the pot circuit that can act as low pass filter ?
With the pot lower_end connected to the star point and nowhere else? I still don´t see this in your circuits.
I don´t see this. What schematic are you talking about?
Klaus
He says the hum sound is high frequencies so he is making a lowpass filter with a 100 ohm resistor in series with the 25 ohm mic and a 2uF capacitor to ground for a 640Hz cutoff of all higher frequencies.Hi,
You know there is no capacitor involved in the pot circuit that can act as low pass filter ?
With the pot lower_end connected to the star point and nowhere else? I still don´t see this in your circuits.
I don´t see this. What schematic are you talking about?
Klaus
Hi,
obvious...
* they are not related to the filter
* both pots are in parallel
* they just act as a variable ohmic load to the input signal.
and if the wiper is at one side, it will short circuit any input signal. (at least for the simulation, but not for a real pot)
For sure there will be no hum anymore.
And you have the simulation tool. So use it.
--> Does the pot position make any difference from 1% to 100%?. I doubt it.
I don´t know what your idea is. That´s why I asked for it. I still don´t know - or not understand.
Klaus
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