Power Supply filtering question

[markm]

In this schem, what is the need for all of the extra .1uF caps in the power supply and, are they really necessary?
And, I am correct in assuming that the Vb voltage is going to be from pin 7 of IC2?
Thanks for the help guys!

[db]

The main 100uF is the main decoupler.  Electrolytics suffer from higher impedance at higher frequencies so usually a low value ceramic or other capacitor is put in parallel to compensate.  The reason for having more than one in that schematic is (I believe) down to the physical positioning.  i.e. dotted around the circuit close to ICs.  It is good practice to have local decoupling of ICs and any other active component which drain current from the supply.

[George Giblet]

The primary reason for the 100nF capacitors found across opamps is to prevent oscillation. 

The power supply tracks have inductance. The impedance of the power supply therefore increases with frequency and this situation can cause opamp circuits to oscillate.  Older opamp tended to be low bandwidth so by the time the inductance comes into play the opamp hasn't got enough gain left to form an oscillator.  The later generation opamp like the NE5532 and LM833 have wider bandwidth an can easily oscillate.

The 100nF caps ensure the supply rail is low impedance at high frequencies and they should/must be located close to the device, and on each device.  In some instances you can get a away with one near two devices etc.

At very high frequencies large caps don't provide a low impedance power rail.  While some layouts might work with suitable one large cap on the main rail alone it's hard to predict when it will work, and it's hard to know if all will be well on the next batch of opamps.   The susceptibility to oscillation depends on the specific circuit, for example feedback caps like C5 can often tame oscillation issues.

The main point is, if know you are dealing with opamps that are susceptible to oscillation using the 100nF cap decreases the likelyhood of oscillation issues.  Leaving them off or trying to skimp means there is a chance some people will have problems with some layouts.