4069 envelope follower
I suspect these are very unstable as I recall the phase shift and BW was very supplier sensitive and as suggested already, this old design may no long be guaranteed to work with any supplier and subject to HF oscillations.

So if you have an Op Amp, you are better off with a precision diode  rectifier and control the desired attack time and decay time for your instrument.

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These handy CD4000 series gates work like inverting OP AMPs  where the ratio determines the Analog Voltage Gain , Av=Rf/Ri over a limited range up to 1000 on buffered gates.

If the input is floating then it will just amplify noise.  

Impressions

You didn't  mention the output voltages of each stage, (do so in future). 

I suspect you neglected to AC couple your signal with a suitable cap that is much lower impedance, Zc(f) than the input Ri.    (33k)

If not sure use a  calculator and if using a polarized cap choose + to input at Vcc/2.

(Zc=1/(2pi*f) with Zc(fmin) &lt; Ri   

Stage 1  Av=-2
Stage 2  Av=-100 with rectifier
Stage 3  Av=-1

You must AC couple your signal into the Input since it it is self biased automatically to ~Vcc/2 with the feedback Rf.

Std practice is 0.1uF across Vdd-Vss. (p14-p7) *must have