stupid question re: series resistors in OD section

[TimS]

I'm looking at the ODS-101-NON-HRM schematic and I see two mods to the series resistors prior to the trim and level pots. The first suggests lowering the 220k resistor before the trim pot to 150k-200k, saying that it will "remove low midrange mud". The second suggests raising the 100k resistor before the level pot to 150k, saying that it will "add upper midrange clarity".

Now for my stupid question: how does that work? I understand how RC highpass and lowpass filters operate, but these are a little different.

[dogears]

The first mod is valid. The second is a typo. It is not a mod. It should not be on there.

The first mod raises the knee and cleans out some bass. It also adds a little high end. You will need to adjust the trimmer to compensate the increased gain of reducing the resistor that feeds it. It is an RC with the CL2 cap.

I'm looking at the ODS-101-NON-HRM schematic and I see two mods to the series resistors prior to the trim and level pots. The first suggests lowering the 220k resistor before the trim pot to 150k-200k, saying that it will "remove low midrange mud". The second suggests raising the 100k resistor before the level pot to 150k, saying that it will "add upper midrange clarity".

Now for my stupid question: how does that work? I understand how RC highpass and lowpass filters operate, but these are a little different.

[TimS]

The first mod is valid. The second is a typo. It is not a mod. It should not be on there.

Ahh, that makes sense. I thought the idea of increasing the resistor value to add upper midrange clarity sounded wrong. If anything, you would want to decrease that value to add high end, right?

The first mod raises the knee and cleans out some bass. It also adds a little high end. You will need to adjust the trimmer to compensate the increased gain of reducing the resistor that feeds it. It is an RC with the CL2 cap.

I guess where I get confused here is in the way the circuit differs from a typical RC, where you have a cap in series with the signal path and a resistor in parallel. Here there's also some series resistance from both the 220k resistor and whatever portion of the pot is "above" the wiper. How do you account for that series resistance when calculating the cutoff frequency?

[dogears]

The series resistance is part of the path to ground. Lowering it, changes the impedence. Thus, raises the knee.

As far as the other "typo" mod, if one were to raise that resistor, the knee would be lowered and you would increase the miller effect. More bass, less highs....

[Bob-I]

Scott mentioned Miller effect, this is really the C in the RC equation. Miller capacitance couples with the series resistance creating the path to ground.

[dogears]

But C is also the interstage coupling caps.....

Scott mentioned Miller effect, this is really the C in the RC equation. Miller capacitance couples with the series resistance creating the path to ground.