Input impedance for spring reverb tank in pedal

[BluffChill]

I've been thinking about making a spring reverb pedal with Belton's mini 'blue' spring reverb tank.
They offer two different ones - with 600 Ohm input impedance, and 150 Ohm. I was wondering which is best if I were going to be putting this in a pedal (ie, before any pre-amplification as if it were in an amplifier)?

http://www.hotroxuk.com/accutronics-blue-reverb-amc2ef3.html
http://www.hotroxuk.com/accutronics-blue-reverb-amc2bf3.html

I'm probably going to go for an op-amp summing mixer based design.

[anotherjim]

For a low voltage pre-amp, I think the lower impedance the better - so that would be 150ohm. A single ended 9v powered amp might still be too weak for a good drive.

[BluffChill]

Thanks jim. It might end up being an 18v job, but I'd really just like one to experiment with. 150 it is. Cheers!