Tonewinner AD-PA+ silver

Two channels, 300 watts per channel into 8 ohms, more than 43 kilos on the scale. The AD-PA+ is the flagship of Tonewinner’s hi-fi range, a Chinese manufacturer active in audio electronics since the early 1990s. This stereo power amplifier operates in class A, class AB, or automatic mode, depending on user preferences or thermal conditions. It succeeds the AD-1PA, from which it inherits the core design with an optimized circuit.

A power supply built for large speakers

The heart of the AD-PA+ is a 1200-watt toroidal transformer, a power rating rarely found in this price category. Each channel has its own dedicated winding on this transformer, which ensures complete electrical separation between the left and right channels.

The current reserve comes from 16 filter capacitors with a total capacity of 180,000 µF. This reserve makes it possible to maintain a stable voltage during sudden current demands, such as percussion strikes or fortissimo orchestral passages. The signal-to-noise ratio exceeds 115 dB on the unbalanced input, a figure that reflects the care taken with the power supply chain.

Class A, class AB, or both depending on temperature

The AD-PA+ offers three operating modes selectable via a front-panel switch. Pure class A provides constant biasing of the output transistors: the signal passes through a stage that is always active, never reaching the cutoff region. This approach eliminates crossover distortion but generates significant heat dissipation, around 260 to 300 watts at idle.

Class AB reduces this consumption to 70–110 watts at idle by only partially biasing the transistors. The compromise lies between the sonic purity of class A and energy efficiency.

The automatic mode monitors the internal temperature and switches from class A to class AB when a critical threshold is reached, then returns to class A once the unit has cooled down. This function prevents thermal shutdowns during long listening sessions at high volume while preserving the benefits of class A when conditions allow.

Eight pairs of transistors per channel

The output stage uses Toshiba TTC5200 and TTA1943 transistors, matched in sets of eight. These bipolar transistors are renowned in the audio amplification world for their linearity and predictable behavior under varying loads. Their arrangement in a three-stage Darlington circuit in BTL (Bridge-Tied Load) configuration makes it possible to drive demanding speakers with authority.

The circuit topology is fully symmetrical: differential input, differential amplification, differential output. This symmetry effectively rejects common-mode interference and contributes to the low stated total harmonic distortion (less than 0.008% at 1 kHz).

Compartmentalized internal layout

The inside of the chassis is divided into separate compartments that physically isolate the transformer, filter capacitors, and amplification circuits. This separation reduces magnetic and electrostatic coupling between sections. The toroidal transformer, by its geometry, already radiates very little outward; its placement in a dedicated space reinforces this isolation.

The left and right channels each occupy their own area of the chassis, with independent heatsinks. On models in the Tonewinner range, the heatsinks are exposed on the sides of the unit, facilitating natural convection.

Connectivity and integration into an existing system

The AD-PA+ accepts two types of inputs: a pair of unbalanced RCA and a pair of balanced XLR. The balanced input will be preferable for long runs to a preamplifier or to maximize the signal-to-noise ratio in installations sensitive to electromagnetic interference.

On the output side, each channel has a double pair of binding posts, allowing bi-wiring to speakers equipped with separate terminals for the bass and mid/tweeter sections. This layout reduces magnetic interactions in the cables and can improve perceived definition on certain systems.

A 12-volt trigger input and output allow the amplifier to be integrated into an automated installation. Tonewinner’s AD-1PRE+ preamplifier, designed as the natural companion to the AD-PA+, can trigger the amplifier’s power-up via this link.

Technical specifications

Highlights

• Power of 2 x 300 W RMS into 8 Ω
• Operation in Class A, AB or Auto
• High-performance 1200 W toroidal transformer
• High current capacity
  • 16 capacitors
  • 180,000 µF
• Unbalanced RCA and balanced XLR inputs
• Bi-wiring capability and automatic trigger

Design

• Class A / AB stereo amplifier
• 1200 W toroidal transformer
• 16 capacitors of 180,000 µF
• Class selection: A, AB, Auto

Measurements

• Power: 2 x 300 W RMS into 8 Ω
• Frequency response: 10 Hz – 100 kHz ±3 dB
• Gain: 29.5 dB ±1 dB
• Signal-to-noise ratio: greater than 115 dB
• Total harmonic distortion: less than 0.008%

Connectivity

• 1 stereo RCA input
• 1 stereo XLR input
• Screw speaker terminals
  • Double pair for bi-wiring
• Trigger input and output

Advantages

• Generous power supply for stable, dynamic power
• Natural, detailed sound reproduction
• Bi-wiring capability and easy integration into any system
• Auto function to switch between Class A and AB depending on temperature

General information

• Dimensions: 444 x 294 x 449 mm
• Weight: 43.4 kg
• Colors: black, silver
• Material: aluminum