I've had this one in mind for a long while. Finally got around to putting it all together the way I wanted recently after finishing the mixer prototype.
I built two so far. One with alpha pots and one with fixed gain. There really isn't proper room for pots so I came up with the following, which was sort of what I originally wanted from the beginning.
I used the lt3265 for the negative rail, left out all the positive rail passives. It switches at 500khz so I figured this might be better than the other inverter offerings that switch closer to audio. The phantom circuit is what I used in the mini mixer- lt8330 into lt3012 Theoretically it should possibly be noisy, but so far in practice there is no audible noise. Measurements might reveal noise though.
Real simple: 1 9V battery, alternate footprint for dc input, on/off power switch, phantom on/off, 10 way grayhill $witches for matched gain settings from 12-66db in 6db increments, 2 mini balanced input jacks, one unbalanced mini out intended to interface with portable recorders, altoids friendly(tm).
There is a little bit of board space now next to the battery, not sure what to do with it.
I have not yet tested battery run time but it should be over 2 hours.
I'd like to have this all turnkey and have them built in china and somehow make them available if there is interest. If china does it properly then the cases can be made with 3 easy hole punches in a mint tin, or 4 if someone wants to use the dc input jack.
render of next version with the grayhill switches
Shutterfly
first build
Shutterfly
I built two so far. One with alpha pots and one with fixed gain. There really isn't proper room for pots so I came up with the following, which was sort of what I originally wanted from the beginning.
I used the lt3265 for the negative rail, left out all the positive rail passives. It switches at 500khz so I figured this might be better than the other inverter offerings that switch closer to audio. The phantom circuit is what I used in the mini mixer- lt8330 into lt3012 Theoretically it should possibly be noisy, but so far in practice there is no audible noise. Measurements might reveal noise though.
Real simple: 1 9V battery, alternate footprint for dc input, on/off power switch, phantom on/off, 10 way grayhill $witches for matched gain settings from 12-66db in 6db increments, 2 mini balanced input jacks, one unbalanced mini out intended to interface with portable recorders, altoids friendly(tm).
There is a little bit of board space now next to the battery, not sure what to do with it.
I have not yet tested battery run time but it should be over 2 hours.
I'd like to have this all turnkey and have them built in china and somehow make them available if there is interest. If china does it properly then the cases can be made with 3 easy hole punches in a mint tin, or 4 if someone wants to use the dc input jack.
render of next version with the grayhill switches
Shutterfly
first build
Shutterfly