K&K Audio / Lundahl Transformers

RE: passive DAC output stage

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Hi David,

Will the Passive Output work on any DAC output stage? That is a broad question and of course the answer is no.

Here are some general guidelines for use with DACs other than the PCM1794.

First, there must be no magnetic flux due to current when the signal is idle. This means that if the input is single-ended, the input must be at 0 volts (or 0 mA) when idle. If the input is differential (push-pull), the voltage (and current) on both inputs must be equal when idle.

Current-to-voltage conversion is always done by a resistor. This resistor may be on the input of the transformer or on the output of the transformer. For the transformer, if the resistor is on the input, think in terms of voltage, if the resistor is on the output, think in terms of current.

When using the transformer for gain, you must know the impedance of the load and consider if the DAC chip can drive this impedance when reflected back through the transformer. Remember, neglecting losses, power gain = 1 through a transformer.

Dave


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