Stereo buffer | preamp with isolated output aimed at 19 Inch rack equipment. Input volume can be boosted up-to 10dB.

This design is intended to be used in a modular configuration, where it functions as the input / output stage for an audio effect or preamp.

This version includes a relay and simple switch connector for toggling the isolation on|off.

Please make sure to check the solderable jumpers that need to be soldered in order for the output buffer to work!

The design is intentionally made to have different gain-staging possibilities depending on the assembly of components.

Transformer isolation:

• Zin ~1M Ohm
• Zout ~600 Ohm
• THD+N @ 1kHz ~0.05% (Increased THD below ~200Hz).
• SNR ~100dB
• Crosstalk ~70dB
• For a flat (±1dB) frequency response: requires an additional load on the output of 680Ohm in series with 10nF.

Without transformer isolation:

• Zout ~0.3 Ohm
• THD+N improves to ~0.0015%
• Frequency response improves to ±0.04dB