Thanks again for all your help, it is very much appreciated.
On the circuit information documentation it says the circuit is "designed for a standard input level 750mv. In case of a lower input level, resistor R1 shall be replaced with a higher rating resistor. Dynamics is determined by the C3 capacitor. Supply voltage: in the range of 9 - 15 v"
The PSU I was going to purchase is 9v, 12v, 15v & 18V (switchable) 1200mA.
Would it be necessary to change R1 because it is 1200mA?
Would I expect to see a difference in brightness between 12v and 15v PSU? (12v ones are much cheaper)
I have accepted that this circuit is not designed for my application so I am treating it as a conceptual design and will live with its faults (LEDs that are not as bright as the could be, inconsistency in brightness across different coloured LEDs)
If it is a successful prototype and the band likes it, I will try to design are better and brighter version from the ground up. At the moment I'm pushed for time and I have already purchased four of the level meter kits so I will have to make do.