Reverse Log taper math

I'm looking to build some ssl 9k preamps and use rotary switches instead of a pot, can anyone point me in to right direction as to how to calculate the values of the resistors I need? I imagine this has been covered, but I've searched and I can't seem to find anything that is clear to me.


Thanks alot.

> how to calculate the values of the resistors I need?

The gain is "the ratio of two resistors".

In most differential mike-amps, "one" of the resistors is really two equal resistors, often 5K, coming from two outputs or an output and ground. Add them together and call it 10K.

We vary the other resistor. If that resisor is 10 ohms, the gain is 10K/10 or 1,000 or 60dB. If it is 100 ohms, it is 10K/100= 100= 40dB. If it is 1K, 1K/100= 10= 20dB.

Almost. Actually you add 1 to the ratio. So "1,000" is really 1,001, 100 is 101. Nobody notices. 10 is really 11, and prissy techs will notice the 1dB error. And if you go as far as 10K, hoping for gain of 1, you really get gain of 2, a 6dB error.

So figure what numbers you want on the knob, work backward, figure your resistors.

Many thanks to both of you... Prr I think I've got a much better understanding now, thank you.

I would say that sumproduct might shorten your formula - ask at Mr Excel if you feel inclined.