Strings of LED's
The image below is from an electronics magazine. The circuit is designed to light a string of LEDs (Light Emitting Diodes) to indicate the intensity of an audio signal presented at "INPUT." The combination of the diode and C1 form a peak detector. As the amplitude of the input increases more of the LED's should light up (i.e., D23 lights for even a small input, but D28 won't light up until the signal gets very large). All of the diodes are standard Silicon diodes (i.e., not ideal) except for the bottom ones (D23-D28), which are LEDs . For our purposes, assume the LEDs have current-voltage characteristics like the other diodes, but emit light when current (>1mA) flows through them. You can use either the constant drop model or the exponential model of a diode (the ideal model is not useful in this case).
Can you explain in two or three sentences (note) why it doesn't work. Can you think of an easy fix?