Calculating Dual Gang Potentiometer calculation

Can some kindly explain to me how to use Ohms law to calculate some potentiometers I need for level control after my console?

I'd like to  have an external headphone level control from my stereo headphone outs -3 dBu no load, -8 dBu 60"

I'd also like to be able to to trim the balanced line level outputs I am sending to the house +4 dBu, Zout ! 100"

I was told to use 100ohm on my headphone, and 600 on the line level but I'd like to understand why, and if that is indeed what I need.

Thanks

The line level outs will be designed to drive a load of 600 ohms or higher so you cannot use a pot value less than 600. You want to maintain as low an output impedance as possible so use the lowest value pot you can which in this case is 600 ohms.

For the phones output, most phones are happy being driven from 100 ohms or less. Your phones output is very probably a very low source impedance (a few ohms if that). A 100 ohm pot will therefore  never look less than 100/4 - 25 ohms to the headphones which is well below the required minimum.

Don't forget any trim pot of this type will only allow you to reduce the available signal level.

Cheers

Ian

qwertypo said:

Can some kindly explain to me how to use Ohms law to calculate some potentiometers I need for level control after my console?

I'd like to  have an external headphone level control from my stereo headphone outs -3 dBu no load, -8 dBu 60"

I'd also like to be able to to trim the balanced line level outputs I am sending to the house +4 dBu, Zout ! 100"

I was told to use 100ohm on my headphone, and 600 on the line level but I'd like to understand why, and if that is indeed what I need.

Thanks

Click to expand...

You need Ohm's law and some maths. Check "voltage divider" and "decibel conversion".

Thanks for the research info!  Very helpful.... I'll do some reading and try to better arm myself for this little project.

cheers

Or you can use pot smaller than 600ohms but make sure you terminate it with a 600 ohm or higher resistance in series with the terminal going to GND.