The old 741 opamp is nearly the slowest opamp available.
The 10uF filter capacitor will take "all day" to charge from the low output current of the opamp.
Use a fast opamp like a TL081 , increase the value of the 100k discharge resistor and reduce the value of the filter capacitor.
PHP:
Or the opamp could drive a transistor emitter-follower to quickly charge the capacitor with a high current. The signal must be 5V or less to avoid reverse breakdown of the transistor's emitter-base. The base-emitter becomes the rectifier.[/QUOTE]
Thanks for the ideas. Do you mean that i should purge after the op-amp using a transistor?
Anyway, i did try to do some simulations by increasing the resistor to 1MHz and the signal look nice. Somehow, if i decreased the input signal to few mV, the output signal seems to be 'clamped' above. May i know that if TL081 could be able to saturate the output signal??? (as a peak-detector)...
Thanks audioguru