Hi, this will hopefully be a pretty straightforward question...this preamp board requires a 12VAC-CT-12VAC input to power up. I read on some reviews that they were able to get it working with batteries or just straight VDC...how would this be possible? I have a power amp that has an auxillary VDC supply (+ and - 18V)...could I use this to power the preamp and if so, how? Hopefully can get around purchasing a ~$20 transformer? Just seems so unusual for such a cheap board. Thanks!
Just connect the +/-18V to the two ac inputs and connect up the ground and it will work. Order of the +/-18V is unimportant. Why?
The rectifier on your board which would rectify the 12V ac will automagically route the right supply polarity to the right opamp pins - that's what rectifiers are about.
And, it so happens, that when you rectify 12V ac, the rectified values comes out very close to 18V DC.
So, you're all set! Just wire it up!
But, if I would do it, I would take out the rectifiers and connect up the +/-18V to the capacitors that were fed by the rectifiers in the original setup. Save a volt drop across the diodes.
Jan
The rectifier on your board which would rectify the 12V ac will automagically route the right supply polarity to the right opamp pins - that's what rectifiers are about.
And, it so happens, that when you rectify 12V ac, the rectified values comes out very close to 18V DC.
So, you're all set! Just wire it up!
But, if I would do it, I would take out the rectifiers and connect up the +/-18V to the capacitors that were fed by the rectifiers in the original setup. Save a volt drop across the diodes.
Jan
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The NE5532 will work from voltage up to and including -/+22 volts and so there is no issue using a clean -/+18 volt supply.
If the board accepts AC voltages direct from a transformer then this means that rectifiers and reservoir caps are already on the board. There should be three connections, a 0V one and two AC inputs.
You could simply connect +18 volts DC and -18 volts DC to the two AC input terminals together with the ground or 0V wire. The bridge rectifier will sort the polarity out, in other words it doesn't matter which way around you connect the two DC input wires.
If the board accepts AC voltages direct from a transformer then this means that rectifiers and reservoir caps are already on the board. There should be three connections, a 0V one and two AC inputs.
You could simply connect +18 volts DC and -18 volts DC to the two AC input terminals together with the ground or 0V wire. The bridge rectifier will sort the polarity out, in other words it doesn't matter which way around you connect the two DC input wires.
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