thanks richard , the second link helped clear why it works ,

i happened to have LM324 onhand and the first cct seems to work well , changing the r4, r9 in the diagram to 200k pot allows easy way to set the best display level as a dephalt setting for the display that is in use for testing , and will go back to a set resistors now that it has been found

the display i am using has a -9.5v VEE generated output , seems best display with -7v ( relative to GND) applied to to V0

for anyone using this cct the OP amp series LM321( single) LM358(duel),LM324(quad) , has a voltage range of upto 32v ( combined 5v + VEE = 32v( VEE upto -27v))

ill do further testing , but i found the best results to be for a freq of 1300 , which gave a smooth voltage output from the op amp , a duty of 140 , ranging from 80 - 200 gave a voltage shift of +/- 2V from pot setting

in the end it was alot easier to use the HPWM command , as the freq required was well below 32767Hz no direct chip register setting up was required

cheers guys