Amplifier operation voltages

Crescendo amplifier in Elektor magazine....
And I have questions about operating voltage of Cresendo ME.
In schematic recommend 45-50 VDC (about 35 VAC) so can I use lower or higher voltages?
I can get transformers with 30 VAC (about 42VDC) or 38 VAC (about 53 VDC).
Which one is better? And do I have make some modifications in schema if I use lower or higher voltages?

Thanks!
 
I have other question now about Crescendo ME.
Can I replace OP77GP with OP07CP, OP27GP or OP37GP. This OP77GP are used in a sort of Offset compensation.
Because I can´t get this OP77GP.

OP77GP Input Offset Voltage -values typical 50yV(micro V) and Max 100yV.
OP07CP Input Offset Voltage -values typical 60yV and Max 150yV.
OP27GP and OP37GP Input Offset Voltage -values typical 30yV and Max 100yV.




Sorry my very bad English... :)