Input Buffer for NC500 and Purifi Audio

Input buffer for HYPEX NC500 and PURIFI AUDIO

The Hypex NC500 and the Purifi Audio 1ET400A are two single-channel, extremely high-quality, analog input power amplifiers modules which operate in class D. They are capable of over 400 W of power and provides an audio quality level that sets the standard for power amplifiers of any operating class. Its compact sizes and high reliability make them fit a broad range of applications, while their audio qualities make them the undisputable choice even in applications where all the premium is on sound quality.

 

Input Buffer for NC500 and Purifi Audio - 1ET400A

Figure 1. Purifi Audio 1ET400A module.

 

However, despite of all these advantages, they are practically devoid of any sonic signature so they require an external input buffer to tuning in a “warm house sound”.

 

Input buffers

Buffers are electronic circuits with unity gain that provide electrical impedance transformation from one circuit to another, with the aim of preventing the signal source from being affected by whatever currents the load may be produced with.

The main element of the buffers are the operational amplifier, whose main characteristics are the very high input impedance and the very low output impedance. These features, together with the rest of the passive components of the circuit, prevent high frequency details from being lost in the signal, resulting in a signal with more “colour and warmth”. In short, a buffer makes the high fidelity system more pleasant to listen to.

 

Design process

At atm audio, we started to design a very low noise input buffer for the Hypex NC500 and the Purifi Audio 1ET400A, taking advantage of its pin compatibility.

After several prototypes and proofs of concept where we tested the operation of the buffer and its correct assembly in the chassis, we finally develop a product where the noise figure was reduce to a minimun. In addition, the footprints of the very low noise voltage regulators and the operational amplifier allowed integrating components of any manufacturer (Burson Audio, SparkosLabs…) into the design, giving the user the possibility to choose the best configuration for their audio system.

 

Input Buffer for NC500 and Purifi Audio First prototype

Figure 2. First prototype of the NC500 input buffer.

 

Input Buffer for NC500 and Purifi Audio Second prototype

Figure 3. Second prototype of the NC500 input buffer.

 

The input buffer was designed in close collaboration with Richard Doporto, of Sonic Imagery Labs, who provided us very valuable technical information to adapt the 994 Enh Ticha operational amplifier to our design so that it fits perfectly with the Hypex NC500, because the module needs a high current to attack the internal drivers and a few operational amplifiers in the market can provide that current.

 

Input Buffer for NC500 and Purifi Audio Final version

Figure 4. Final version of the NC500 input buffer.

 

Input Buffer for NC500 and Purifi Audio Front

Figure 5. Front view of the NC500 input buffer front view.

 

Input Buffer for NC500 and Purifi Audio Side

Figure 6. Side view of the NC500 input buffer.

 

Input Buffer for NC500 and Purifi Audio Assembled

Figure 7. The NC500 input buffer plugged into the power module.

 

Measures

Different measurements were made on the circuit using different operational amplifiers to check the behaviour of each of them individually and see how one option or another can affect the sound in the power module.

The operational amplifiers used were:

  • LM4562
  • LME49720
  • MUSES01
  • Burson Audio V5
  • Sparkos Labs SS3602
  • Sonic Imagery Labs SIL994

To perform the measurements, an Audio Precision distortion analyzer model APX515 was used.

These were the results:

Input Buffer for NC500 Spectral density mounting a LM4562

Figure 8. Spectral density of the NC500 mounting a LM4562.

 

Input Buffer for NC500 Spectral density mounting a LME49710

Figure 9. Spectral density of the NC500 mounting a LME49820.

 

Input Buffer for NC500 Spectral density mounting a MUSES01

Figure 10. Spectral density of the NC500 mounting a MUSES01.

 

Input Buffer for NC500 Spectral density mounting a Burson Audio V5

Figure 11. Spectral density of the NC500 mounting a Burson Audio V5.

 

Input Buffer for NC500 Spectral density mounting a SS3602

Figure 12. Spectral density of the NC500 mounting a Sparkos Labs SS3602.

 

Input Buffer for NC500 Spectral density mounting a SIL994

Figure 13. Spectral density of the NC500 mounting a Sonic Imagery SIL994.

 

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