Op Amp peak detector not working
First of all an LM741 is like a dinosaur. It is ancient technology which means odd behaviour at times. R2 at 1 K is much to low for the op-amp to drive. As suggested in comments make it at least 10 K. Use a quality op-amp like a TL071 JFET. It will not load down feedback and input resistors and has very low distortion.

Use of the TL071 is best if you have a +/- 12 volt rails, so the (+) input is common ground in the center of the power rails. You can use an OP220EZ for single ended supply up to 30 volts, but it cost a bit more. If you use a single ended supply you should have a DC blocking capacitor on the input, so any DC offset is blocked.

No matter which op-amp you use keep R2 at least 10 K, as most op-amps can supply only 5 mA at most. Keep the capacitor at 10 uF or less so you get close to true peaks.

If you want a faster decay time put a 10 K (minimum) resistor in parallel with the capacitor. A 0.1 uF capacitor will give a fast response to peaks but not hold the value for long, unless your decay resistor is upped to 100 K or so.

With extra diodes and a two potentiometers you can control both attack and decay times.

This would be a better version of what you posted:







simulate this circuit &ndash; Schematic created using CircuitLab