I'm looking for a 9v transformer that I can use as my ac voltage reference that I can wire directly to (I want to put this in a case with other components, and don't want to have to plug the transformer directly into a 13a socket). Most I see have dual secondaries, either separate or centre tapped.
If I don't load the secondaries that I'm not using for the the reference, and leave unconnected, will that affect the waveform?
Also, will a slightly larger transformer than what would be required by just looking at the current requirements give a better shape waveform?
Thanks
Lloyd
Re: 9v ac transformer choice
It should not.
The current required is to all intents and purposes zero (0.1 uA or so). A larger transformer is likely to have better regulation (the voltage rise when unloaded). But much more importantly, get a transformer whose primary is rated correctly for your mains voltage (i.e. if you are in the UK, a 250 V primary will give you less distortion than a 230 V primary). You can always tweak the calibration or the voltage divider resistors if needs be.