[vline~] is not a lowpass filter, so I guess you use [vline~] to control a signal controlled lowpass filter. To make this exponentional you could connect [vline~] to the right inlet of [pow~] and make sure the output of [vline~] is [0-1] (and never exceeds 1). Then choose your range (e.g. [500-1000]). Connect [sig~ 2] to the left inlet of [pow~] and multiply the output by 500. To scale the range, just use [*~] or [/~] and never [+~] or [-~], for you're working on an exponential scale. This means that an output of 0 is impossible, so for a logarithmic amplitude control choose a very large range (e.g. 1-100000) and divide the output by the same value to get the range [1/100000-1].

Hope this helps.