Toshiba SD-3990

After circuit trace...

Note: I have removed the two muting transistors since above photo was taken. This resulted in a subtle improvement in audio fidelity. Continuing the mod...

PeAK from head-fi.org traced the PCB out a bit more:

Next steps:

Determine whether Zoran DAC produces current-output or voltage-output.

If latter, then one can bypass all stock circuitry -- including 4558 op amp -- between DAC and output jack. And follow up by connecting DAC output to 30-gauge and create a new output circuit, with high-quality capacitors (e.g. Auricap, Solen, Hovland, and Sonicaps) and better RCA output jacks. May require an op amp or buffer as used by Reference Audio Mods (Burr-Brown BUF634).

If former, replace 4558 op amp with OPA637, BUF634 or other.

Questions:

What are A in- and B in- on the op amp used for?

For more information and price, click the link or image below...

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