Tremolo easter egg whilst building a Wattson EFY-6

[Addy Bart]

I got a nice surprise when voltage starving the circuit:

https://youtu.be/OvmXb8X2sN4

So my question is what's causing it to tremolo? As you can hear in the video, it kicks in when the level drops below a certain point. It's quite a fun extra to an already great superfuzz! The rate is also somewhat adjustable via the voltage starve pot (5kB).

I didn't have the NTE109 diodes the circuit uses so instead I put a couple of 1N34A in.

[nzCdog]

Cool discovery... sounds fun