As most people here probably know the preamp runs on a single +48v power supply.  I'd like to see if I an utilize some higher quality dual rail power supplies that I have, but I'm not quite sure how to do it.  For the sake of this thread lets say it will use +/-16v.  From looking at the schematics, I think it could be done by keeping +48v as is, removing any jumper from the BD681 spot and injecting the +16v into the  Emitter hole of the bd681 spot and then.... not sure.  Any help is greatly appreciated!


Talk to Joe at JLM. Super nice and helpful guy


Leave out the parts I crossed. Replace the lower 10k with a wire bridge. Like you said connect the +16V  at the emitter of the BD861 (why are there no designators in the schematic). For the negative supply voltage you have to cut the ground connection of the opamp and connect it to -16V. Which is where you might run into a problem if it is not a ground trace but a plane on the pcb. If that's the case and you plan on using the dual opamp, you could bend up the pin and solder -16V to it directly. If you want to use the DOA, leave out the socket, make sure the pin is isolated from the pcb and connect it directly.

From the schematic it seems that there are no additional filter capacitors on the supply line after the regulator. You should try and add at least a 100nF ceramic capacitor from both +-16V to ground, and keep the wiring to the supply short.

Overall, you're probably better off just getting a APi 312 pcb or something similar.

Thank you Volker!  This pretty much confirms what I was thinking.  I inspected the pcb with a flashlight, and it looks like cutting the ground connection for the -16v will be easier than I thought.   There is an additional smoothing cap on the + side but not on - side.  Thanks again, I'll experiment and see if I can get it to work.


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