How about an amplifier and buffer stage in front...
I was looking for the simplest signal detector that I could find for a twin noise gate type thingie I had to do few years ago. I have one mixer project which I maybe never get done ready so I know I might need such detectors anyway, so was looking for these.
I have an old circuit somewhere, it is just one cmos 555 monostable and few passive parts, treshold is set with multiturn pot and audio signal is taken with a cap to the chip, and if reference voltage set with pot plus signal peak is enough, even short peaks are easily seen because you can tailor the monostable time long enough. I did not build it because the project text told that you can zap the cmos 555 if you feed signal in when the unit is not powered. I think it can not detect unsymmetrical signals not so accurately but who cares if it does the job.
For my opto gate project I used TLC271 comparator and put 555 retriggerable monostable after that, worked like dream. Maybe I could have done it with just one 555 but I did not want it to stop working...
If I remeber well there was a peak detector circuit in Cristmas (or was it Summer) Elektor done with cmos gate, tuned near changeover with a trimmer and signal applied there with a cap...
I have old Alesis Microverb somewhere, it has nice tricolor led input level indicator. Both leds light when thre is no signal or it is low level (I dont have the words for the colour, sorry my english) and goes green when signal level is "normal" level, and finally bright red when input is overloaded. Could be done with few opamps...