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11-26-2018, 06:58 PM
Hi jmcd
Your drawing shows a standard high-pass filter, which is opposite to the MV situation, but we can use it anyway.
As R is made smaller, the roll-off point for the high-pass filter moves upward in frequency, and that is what happens as the MV wiper is swept from one end of the pot to the other. At the half-resistance point, 500k is in series with the signal and 500k is in parallel for a net effect of 250k. In circuit analysis, these portions of the pot are effectively in parallel, so you can see that as the wiper is moved from the half-resistance position towards either end, the net resistance goes to zero.
In your circuit, R can be made variable and you have the same result.
Now add a fixed-R in series with the cap. Changing the original R still has an effect but it always adds to the fixed-R and there is no a limit as to how high the bass roll-off can shift upwards in frequency - the new maximum bass roll-off frequency is much lower than without the fixed-R.
Your drawing shows a standard high-pass filter, which is opposite to the MV situation, but we can use it anyway.
As R is made smaller, the roll-off point for the high-pass filter moves upward in frequency, and that is what happens as the MV wiper is swept from one end of the pot to the other. At the half-resistance point, 500k is in series with the signal and 500k is in parallel for a net effect of 250k. In circuit analysis, these portions of the pot are effectively in parallel, so you can see that as the wiper is moved from the half-resistance position towards either end, the net resistance goes to zero.
In your circuit, R can be made variable and you have the same result.
Now add a fixed-R in series with the cap. Changing the original R still has an effect but it always adds to the fixed-R and there is no a limit as to how high the bass roll-off can shift upwards in frequency - the new maximum bass roll-off frequency is much lower than without the fixed-R.
