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Hi-Z to Balanced Line Level Converter

Posted December 16th, 2013 by

Presented is a schematic for a simple circuit with a high-impedance, unbalanced input suitable for an electric (or bass) guitar or some sort of piezo pickup, and balanced, line-level output suitable for use with an audio interface with an appropriate input.

Hi-Z to Line-Level converter schematic

It is a simple circuit consisting of a non-inverting FET-input op-amp gain stage providing the ‘hot’ output, which then goes through a unity gain inverter (or gain of -1) stage which provides the ‘cold’ output. 10pF capacitors may be placed in parallel with the 22k resistors in the feedback loop (R4, R6, R10, R12) to counter oscillation, but these have been proven unnecessary in my prototyping.

Be sure to place the 0.1uF capacitors (C3 to C6) as close as possible to the op-amp supply pins to ensure stability and clean power. This circuit may be powered by the power supply shown here.

Other op-amps may be substituted, but IC1 should be FET-input for the high input impedance necessary.

Gain is varied using potentiometers R3 and R9, and these should be anti-log (or reverse taper logarithmic) potentiometers, or, if these prove to be unattainable, linear. (Do not use regular logarithmic potentiometers; these will be uncontrollable.)

Also, 100 ohm resistors may be placed in series with the hot and cold outputs and these may tame oscillations.

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