# Through-Zero waveforms

When I say ‘Through Zero’ I mean the waveform goes positive and negative, if you generate a waveform with a DAC for example, whatever that wave might be: sine, triangle, saw: the wave will sit on the 0 volt line (if you look on an oscilloscope)

To get the centre of the wave at 0, so the top half is +ve and the bottom half is -ve (you’re AC sine wave at home is like this) then we can use a simple op amp circuit, an inverting summing amplifier with a reference to a negative voltage. Resistor values: Alot is open to experimentation but I use Rin: 100K, Rf: 100K (gain of 1, so same out as in)
R1 and RV1, the RV is a trimmer to adjust the zero cross point, so this could be 100K or so as it’s adjustable. R1 I’d put to 47K at -5 volts and 220K at -15 volts, again connect a source and oscilloscope and experiment.

The setting of the zero point can be adjusted but this is related to the input voltage, so if you have a waveform that changes amplitude then this circuit would need to be placed where the voltage was stable. So if you have a VCA or something then you would put this before that.

The purpose of this is mainly as an educational experiment, you could use this to match a waveform generated by another part of a synth for example, or if you wanted to design a function generator then you could use this circuit.