I have a couple of active PA monitors with only unbalanced inputs. I want to be able to use the balanced monitor outputs from my mixer, so I am planning to build in a balanced to unbalanced converter in each monitor. I have build the boards using NE5532s. These works fine, then my next step should be to make a power supply taking power from the power lines for the amplifier and regulating it to approx +/- 15V using LM317 / LM337.
When I measured the power supply of the amplifier, it turned out to run on +/- 58V. As the NE5532s are rated to run at up to +/-22 V (recommended up to +/-15) and the LM317 / LM 337 can take a voltage drop of 40V, this should just work, but I do not like it - it is a bit too close to the limits. As I measured the voltage of the amplifier across the filter caps without any signal, the voltage will probably be slightly lower under normal use, but anyhow...
At the moment think I have these possibilities:
- Run it as planned, since the circuit is not pulling much current (< 100mA), it will probably work fine.
- Try to find other power lines in the amplifier with lower voltage. This may be more difficult and a bigger risk of somehow creating problems for the amplifier.
- Running two sets of LM317 / 337s in tandem, i.e. using the first stage to get from 58 to 30V then the next from 30 to 15. - I have never seen this been done, a slight waste of components, but I cannot see any reason why it should not work.
- Use some other voltage regulators, integrated or discrete, that can take a higher voltage drop. The only reason to use the LM317/LM337 is that I have a few of them in storage. But are there any recommended voltage regulators that can take a voltage drop in the order of 40V? The monitors are old Laneys, so I do not think I want to put a switched voltage regulator too close to the active circuits.
What would you recommend? Maybe I even have overlooked some possibilities...