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circuit. This will unbalance the input impedance of the circuit. To restore the balance the 1 meg resistor that connects to ground and the positive input should be replaced with a 50K resistor, which when paralleled with the effective impedance of the resistor string will equal the value of the input impedance of the negative input. (This could have been included in the schematic, but at the risk of confusing many a reader. It is amazing how often we must first learn what is wrong first before we can learn what is right.)
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global feedback, and a single polarity power supply.
For those listeners that primarily listen to vinyl, a balanced phono preamplifier is a great idea. The phono cartridge has two output leads per channel and they usually floating, i.e. they are not connected to ground via the case. This allows us to reference their output to ground through a voltage divider and treat their output as a balanced source. Next month we will go in to detail how this can be done.
// JRB
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Uses
Now that we have devised a virtual transformer that converts balanced signals to an unbalanced output, what do we do with it? Obviously, if we have a balanced microphone preamp and an unbalanced preamplifier, this converter will come in handy.
There are more this circuit could be used for than converting balanced sources to unbalanced ones. This circuit can be used inside an amplifier that has an unbalanced input and output. An example is shown above. The fist stage is a simple Grounded Cathode amplifier that cascades into a Split load phase splitter. The two 100k resistors are used to drop the plate voltage of the first stage to half its value. The top resistor is not bypassed by a capacitor the signal level will drop with the DC voltage level. (This was done so as to equalize the power supply noise at the output of the phase splitter, which I turn would be cancelled by the final stage.) The Split load phase splitter converts the unbalanced signal into balanced without adding any gain. The last stage receives the balanced signal and converts it back to unbalanced and provides a low output impedance. This amplifier is the anti-Op-Amp in many ways, low gain no
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