Amplifier Board Design Assistance

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Goal: build only the output/driver stage on ±80 V for 8 Ω using seven complementary pairs of 2SC5200 and 2SA1943 with emitter feedback.

Plan:

Place 7× NPN/PNP pairs in parallel; add per-device emitter ballast Generic Resistor and base-stopper Generic Resistor.
Create a Kelvin-sensed summed emitter node for feedback; expose input-from-VAS and feedback pins.
Add high-voltage driver pair and Vbe multiplier (bias spreader with trimmer) mounted to the heatsink.
Add output network: Zobel Generic Resistor+Generic Capacitor, and series L//R Generic Inductor+Generic Resistor.
Add rail and speaker connectors, star ground, test points; name nets and review.

Questions:

EF2 or EF3 output topology?
Target idle bias per pair (e.g., low, medium, high)?
Include VI limiter pads and thermal sensor pads now?

Click Start on the plan bar to begin and I’ll implement this stage.

Plan

#Goal

Design a high-power output/driver stage for an audio amplifier using seven complementary pairs of 2SC5200 (NPN) and 2SA1943 (PNP) transistors powered by ±80 V rails. The design will drive an 8 Ω load while incorporating emitter feedback via ballast resistors, base stopper resistors for stability, a defined feedback sense node, a driver pair with a thermally tracking Vbe multiplier bias circuit, and an output stability network (Zobel network and series L//R) to ensure proper operation and current sharing.

#Implementation plan

Output Stage Assembly
1. Add seven complementary pairs of 2SC5200/2SA1943 transistors to the schematic. Ensure that each transistor entry includes B, C, and E terminals with proper pinouts.
2. Connect ±80 V rails to the collector nodes appropriately for each pair.
3. Attach individual emitter ballast resistors to each transistor’s emitter for current sharing and thermal stability.
4. Include base-stopper resistors on each transistor’s base to suppress high-frequency oscillations.
Feedback Node and Driver Integration
1. Define and expose a feedback takeoff node at the combined emitter node (or Kelvin-sense connection) summing the emitter resistors’ outputs.
2. Connect the feedback sense node to further stages (e.g., error amplifier in VAS) as required by system integration.
3. Integrate a driver pair stage as needed, referencing the VAS input for local driving to the output stage.
Bias and Stability Network
1. Add a thermally tracking Vbe multiplier (bias spreader) circuit on the heatsink, with an adjustable trimmer, to establish the proper bias voltage across the output stage.
2. Implement an output stability network including a Zobel network (capacitor and resistor) across the speaker output along with a series inductor and resistor to optimize high-frequency stability.
**Interconnections and Net Naming
1. Connect the emitter resistors to form the feedback takeoff node and ensure proper conduction with the bias network.
2. Connect power rails, feedback node, and speaker output properly according to design requirements.
3. Add test points for key nodes including input (VAS), feedback, and speaker output.
Design Review and Validation
1. Review all net connections to ensure correct emitter feedback, bias tracking, and stability networks are in place.
2. Verify the design for current sharing, thermal bias, and overall circuit stability before finalizing the schematic.

#Success criteria

All seven 2SC5200/2SA1943 complementary pairs are correctly placed with proper connections to ±80 V rails and include individual emitter ballast resistors.
The feedback takeoff node is properly formed from the emitter resistor network and connected to the external VAS input.
A driver pair and thermally tracking Vbe multiplier circuit are integrated to provide stable biasing across the output stage.
The output stability network (Zobel, series L//R) is correctly implemented and connected to the speaker output, ensuring overall circuit stability.

Clarify topology

Ask for specific values

Emitter feedback detail

Protection options

Thermal/bias details

Reviews

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