30 May 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.
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”.
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.
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.
Figure 2. First prototype of the NC500 input buffer.
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.
Figure 4. Final version of the NC500 input buffer.
Figure 5. Front view of the NC500 input buffer front view.
Figure 6. Side view of the NC500 input buffer.
Figure 7. The NC500 input buffer plugged into the power module.
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:
- 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:
Figure 8. Spectral density of the NC500 mounting a LM4562.
Figure 9. Spectral density of the NC500 mounting a LME49820.
Figure 10. Spectral density of the NC500 mounting a MUSES01.
Figure 11. Spectral density of the NC500 mounting a Burson Audio V5.
Figure 12. Spectral density of the NC500 mounting a Sparkos Labs SS3602.
Figure 13. Spectral density of the NC500 mounting a Sonic Imagery SIL994.