Okay... been trying to improve my DC-DC power supply.
The "frying bacon" sound has been greatly reduced... still there, but very much reduced. Added inductors and caps to the proto board.
If you put your ears maybe 1-1.5" above the PCB, you'd hear it coming from the inductor.... in the inverting section -18V.
I checked the PSU outputs via oscilloscopes... ripple is about 20mV, with some spikes going up to 50mV at very high frequencies... (what freq? I didn't measure... but based on the Switching PSU design, probably about 75Khz.)
So using an SC-1 with a MINI-IO board module as my load... set the preamp gain to 54dB
, unterminated XLR inputs, I recorded the resulting output hiss/hum/noise....
What do you think?
I *think* it's pretty good and okay, but am wondering if it can still be further improved.
So I think prototype #002 is finalized and we got a good DC-DC PSU here.
Next... I'll build prototype #003 and see if we can improve it further, and wring out the last possible performance out of this PSU.
I've started a redesign of a new PCB design revision too... made the critical paths shorter to reduce RF noise... will also try to add the additional caps I added on the prototype to the final board design.