In your case where you only need to source 1 or 2 opamp chips you can use a voltage inverter which can be made from a 555 timer or you can get a dedicated voltage inverter IC (Often called Charge Pumps).... You will lose a couple of volts so with a 12 volt supply I'd shoot for +/- 8V which will still give you more than enough headroom and use 78L08 and 79L08 regulators to clean things up (This will also help isolate the audio circuit power supply from the RF power supply) ... I'd also consider building the inverter in a PCB box or other small shielded enclosure because although the inverter only runs at a few khz, it is a square wave before filtering and regulation with plenty of harmonics in the LF region ... You'll also want to keep the fundamental out of the audio circuits
Just Google '555 voltage inverter' and you find plenty of circuits When done correctly this is actually a better solution than using a center tapped transformer dual supply because you end up with a fairly high amount of current in the positive side and very little in the negative supply which leads to imbalance which can make noise induced into the supply a bigger problem ... The inverter circuit helps to avoid this when you only need less than 100mA negative supply as long as it's well filtered and shielded JR --- In [email protected], "Adnan Yusuf" <[EMAIL PROTECTED]> wrote: > > i was making the sdr for the masses circuit, and came a cross this > problem. How do i give the lt1115 ic +12v power and -12v power at the > same time. >
