We are proud to present AUDIOPHONICS HPA-S400ET, a class D stereo power amplifier based on two PURIFI 1ET400A modules. This ready-to-use version is designed for audiophiles needing a foolproof amplification solution, with a considerable power reserve as well as impeccable linearity. The PURIFI modules are indeed among the most rigorous Class D amplification solutions on the market, with simply exceptional measured performance.

This device offers high level sound reproduction which will be suitable to drive demanding speakers, to sonorize large listening rooms or for studio applications requiring a considerable headroom without compromising on the precision and richness of the audio message.

All of the components are integrated in a sober and robust 100% Aluminum housing with openings and heatsinks to help heat dissipation. Its design also allows it to block signal interference.

• The output noise is negligible, which allows deep silences and prevents losing details when listening at low volume.
• The circuit benefits from a high level of rejection (PSRR) which minimizes the impact of power supply on audio performance.
• Load-invariant frequency response and negligible output impedance enables the HPA-S400ET to drive the most demanding speakers with ease.
• Very low idle losses and reduced electromagnetic interference (EMI). The High loop gain allows relaxed timing of the power MOSFETs without degrading audio performance.
• The HPA-S400ET uses these amplifier modules with an interface card specially developed for optimal integration.

Audiophonics Interface Card

Both modules are driven in opposite phase, to cancel out the «Power-Supply Pumping» effect. This allows greater stability in the power supply by alternately distributing current draws on each rail, thus increasing its overall capacities.

We opted for a regulation with two voltage levels in order to optimize the power supply to the PDOs and the auxiliary voltage supplied to the modules. This allows the OPAs to be powered with a high voltage (18V) for better overall performance, and allows them in turn to provide the voltage needed to reach the amplifier's maximum output level. While still maintaining the auxiliary voltage required by the modules.

Each channel uses its own Analog Devices OP275 AOP. they are based on a hybrid Bipolar / JFET technology. bringing precision and musicality. They are mounted on a socket allowing their possible replacement.

To suit all uses we opted for 3 gain settings, adjustable by jumper on the interface card:

• Gain of + 7.2dB, for a total of 20dB (default) - Maximum power reached with a signal of ~ 4.2V RMS
• Gain of + 12.5dB, for a total of 25.3dB - Maximum power reached with a signal of ~ 2.2V RMS
• Bypass: in this case the signal passes directly from the inputs to the modules, allowing the lowest possible gain of 12.8dB. This mode can be interesting when using a powerful preamplifier, capable of driving a load of 2 to 4kOhm and reaching a voltage of ~ 10V RMS

Connectivity

Designed for easy integration, the HPA-S400ET has a balanced stereo (XLR) and unbalanced (RCA) input. Bipolar selectors make it easy to change the input source and even allow independent channel control.

On output side, BP-207 Carbon / Gold 24K Ø5.5mm speaker terminals ensure excellent connection with the speakers.

THD+N

Frequency response

THD vs Freq