Anyone have a diagram / parts list for a good low noise 48v phantom power supply? Want to build a couple in stompboxes with XLR in/outs to power condenser mics into my tascam m312 mixer.
thanks!
Posted Jun 16, 2021, 3:47 AM UTC
FWIW, most condensers drop the voltage internally to 5 or 6 volts. You may be able to get by with just the 9V supply. If not, you can use a charge pump to step it up to 18V.
This is sort of true. The phantom power standard is 48V with a 3.4k source resistance (the 48V voltage source is connected to each differential signal line by a 6.81k <0.3% resistor). So as the mic's current draw increases, obviously the voltage available will drop across the source resistance.
There may be some mics that will run on 9V with low/no source resistance, but the only way to guarantee compatibility with all phantom-powered mics is to do 48V with the correct source resistance.
Here's Jorg Wuttke's analysis of the P48 standard:
https://www.microphone-data.com/media/filestore/articles/The%20feeble%20phantom-10\_.pdf
Yes, but if you look OP's question, they're wanting to build it into the stompbox itself. There's no need to add in a 48V step-up converter, which are hard to come by, when you can power the average condenser off the existing low voltage supply, provided the source resistances are adjusted accordingly. For a 9V supply, that would mean dividing the source resistance by about 5, which comes to 680. Close parallel resistor values are 1.2k and 1.5k. From the paper you referenced, "the current actually drawn by modern condenser microphones is typically at least 2 mA, with many products requiring 3 to 5 mA." A 5 mA draw across a 600R source resistance (parallel 1.2k) results in a voltage drop of 3V, which leaves 6V for the mic, and the 1.2k resistors won't load the mic too much. Will that not be enough for some mics or compress some transients? Sure. But stompboxes aren't exactly hi-fi. Better to keep it simple IMO.
https://sound-au.com/project30c.htm down a ways. You can power it with a voltage multiplier or any 48 V switching supply.