convert 0v to -13.5v, trigger a sample and hold circuit

i am trying to modify an old synthesizer to accept a 0v / 5v or 15v trigger input to trigger a sample / hold circuit.

currently there is a slider that controls the sample time (frequency) of a sample and hold circuit. the dc output on scope after the slider/op amp circuit looks like a -13.5 / +13.5 v square wave, which charges/discharges a cap into the sample and hold circuit.

so, my input signal would be a gate, where when i am doing nothing the input signal is 0v, and the output into the circuit during the 0v input should be -13.5v. when i trigger a gate (which i can set to either 5v+ or 15v+ depending on which way makes the circuit easier to implement) i would like the signal to move from -13.5 to +13.5v while the gate is held. when the gate is released and the input moves back to 0v i want the output to be -13.5 again.

here is an example of what the input would look like and what i need the output to look like:
**broken link removed**

Added after 5 minutes:

sorry got excited before finishing thoughts, if anyone has any ideas for how to accomplish this it would be great. ideally to power the circuit i can tap into the -15/+15v/ground already running in the synth. thanks for any suggestions in advance!

Hi, I think its a simple (+/-15V supplyed)OpAmp application...
You can the "zero in leve"l to -12-13V output shift & with the logic 1 (+5V in pulse) try i.e. a factor 2 amplifing/ or comparation for +12-+13V output
Some poormans solution can be, what bunalmis loaded up in 2003 to EdaBoard ..
K.

thanks i have been looking at opamps but im no engineer. i have limited knowledge of actual design and electronic engineering, but am ok to follow schematics. if you have any further details that would be excellent..

Added after 4 hours 6 minutes:

are you able to point to a type of op amp application i can model?

https://en.wikipedia.org/wiki/Operational_amplifier_applications

Hi,
ou can refer pls. to "Differential amplifier" part of that side. ://en.wikipedia.org/wiki/File:Op-Amp_Differential_Amplifier.svg
If calculate it i.e. with 10 & 20Kohms & U1=ca+13V; at U2=0V you will have an output of ca.+13V....
(U1 is best to have from an other OpAmp used as simple Buffer/voltage follower of your +13V voltage attenuator)...
K.

thanks! i will check it out. much appreciated.