rev log 12 pos switch

[josan]

So I have a JLM board that requires a 2 gang 10k rev log pot if I want to use a 12 position 2 gang how would I go about determining r values as related to a rev log pot.

 

[JLM Audio]

Answer the questions below and I will calculate the resistor values for you.

Maximum gain do you would like?
Input transformer ratio are you using?
Output transformer ratio or not fitted?
Dual or single 99v,990,993 etc?

Joe

www.jlmaudio.com

 

[Guest]

Is there an online calculator for this? Though not related to the JLM kit I would like to figure out the resistor values for an API style pre with a 25K rlog taper. 1:10 input trasformer, 40 dB opamp gain range with 5 dB per step. 9 positions total.

Cheers,

elco

 

[Samuel Groner]

The math is not that difficult.

R=R_feedback/(10^(gain/20)-1)

where R_feedback is the resistor between opamp out and -in and R the resistor between -in and ground.

I did a quick-and-dirty Excel file for that:

http://n.ethz.ch/student/groners/download/DIY/GainCalculator.xls

Not well documented and tested yet, I hope you get it...
Samuel