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The Tårns Audio 2Diffseries 225C is a high-power, fully discrete Class-AB audio power amplifier designed around a dual differential input topology with global negative feedback for low distortion and high stability.
It delivers 225 W RMS into 4 Ω, powered from a high-voltage split supply, providing strong current capability and reliable control of low-impedance loads. The amplifier features a wide but deliberately controlled bandwidth, with a frequency response of 5 Hz to 23.6 kHz (–1 dB), ensuring flat audio performance across the audible range while maintaining excellent stability with real loudspeaker loads.
With an input sensitivity of 618 mV, the gain structure is optimized for compatibility with standard line-level sources and preamplifiers, allowing full output without excessive front-end amplification.
The design employs:
• Dual differential input stages for high CMRR and low DC offset
• A dominant-pole compensated VAS for stable global feedback
• Thermally compensated Class-AB biasing
• Parallel output transistors with emitter resistors for current sharing
• Output Zobel network and series inductor for load-independent stability
Expected THD (Total Harmonic Distortion)
1 kHz, rated operating conditions
At 1 W into 4–8 Ω
• THD: 0.003 % – 0.01 %
• Dominated by 2nd and 3rd harmonics
• Essentially inaudible
At 10–50 W
• THD: 0.005 % – 0.02 %
• Sweet spot of operation
• Core stages still well within linear region
At rated power (≈225 W RMS @ 4 Ω)
• THD: 0.03 % – 0.08 %
• Rise caused mainly by:
• Output stage stress
• Supply sag
• Finite open-loop gain at HF
This is normal and correct for a conservatively biased Class-AB amplifier.
Overall character: a robust, conservative, professional-grade amplifier focused on stability, low distortion, and long-term reliability, rather than extreme bandwidth or marginal operating points.
Tårns Audio designs amplifiers the way professional engineers do: conservative, stable, honest in power, and optimized for real loudspeakers rather than laboratory ideals.
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