The 470K on the Q1 base of the Buzzaround

[mordechai]

I've seen a few circuits out there that are versions of the original Buzzaround, but they up the value of the 470K to 680K.  What effect does this have?  Does it make the Q1-Q2 darlington pair drive Q3 a little harder when the resistor is at 470K, and a bit less intense when upped to 680K?

[Rob Strand]

What effect does this have?  Does it make the Q1-Q2 darlington pair drive Q3 a little harder when the resistor is at 470K, and a bit less intense when upped to 680K?

It would do that if the transistors were kept the same.   (Harder in the sense of more collector currents, not intense in sound.)

I suspect the reason the resistor is tweaked is to compensate for variations in the gain (or leakage) of the transistors.  Not all transistors are alike so we tweak the resistors to make the circuit behave like the ideal case.   A good measure of things being equal is the collector voltage of the Darlington.   For that circuit a good starting point would be a collector voltage of 5V (I saw someone post 5.18V).  One way to tweak the collector voltage is to adjust the 680k/470k resistor.  There are other ways to tweak the collector voltage, like adjusting the collector resistor value instead.