Deep Blue Delay with Expression Pedal Jack

[Getomonk]

Hi

I am going to build the Deep Blue Delay for my next project and would like to add an expression pedal jack to control the MIX remotely.

According to the information here: http://www.geofex.com/Article_Folders/xprnped.htm the mod itself should be relatively simple. But as for the expression pedal I would like to use my Ernie Ball VpJr with a TRS Cable like shown here: http://www.strymon.net/2011/10/10/strymon-tech-corner-3-volume-pedal-as-an-expression-pedal/

The article on adding an expression pedal jack states that I need to use a pot for the expression that matches the one in the effect - in this case a 50k lin. The pot in my VPJr is 250k log. I know that the taper is going to be different when using an audio pot, but how much will the added value matter?

Alternatively i have a broken Crybaby lying around that can be rebuilt.

[nocentelli]

I think it might work without any modification (e.g. parallel resistors to lower the effective value of the pot from 250k 50k). The mix pot is just a voltage divider, with the wiper sending a fraction of the delayed signal to the mixer opamp: in these circumstances, the value of the pot used for the divider is rarely critical to the successful operation of the circuit. You just need to wire a switching stereo jack to the mix pot lugs, so when the expression jack is inserted, it disconnects the on-board mix pot and connects the expression pot in it's place; if you want the same value you could connect a 68k resistor across the outer lugs on the switched jack.

[Getomonk]

Thanks for the reply. I thought that would probably be the case,  since the information I have found elsewhere states that the pot value is only critical when it is wired as a variable resistor. In the Secret Life of Pots it says that wiring a resistor from the wiper to the cw lug will make a linear pot behave like a log. If I would like to try that to make the log pot behave more like a linear one (which I have read somewhere is possible) does the resistor value still need to be 68k?