Giving up on Class D

Amplifier is the muscle behind every system, since I am running almost everything digitally, this is the only place I can add a bit of flavor to the character of music I like. I have tried hypex Class D amp before. They are good – powerful and detailed. But I also found them boring and tasteless. Not my taste after all. After a long listening session, I gets headache.

Back to google and I found Aussie Amp. They sell modules with Mosfet as power transistors. As we all know, Mosfet gives a warm sound and there are many who gave very positive feedback on Anthony’s amp. So I bought a few from him.

There are a number of features used in this design

  • Two Stage Nested Feedback Network
  • Complementary Folded Cascode Input stage
  • Improved Gate output stage protection
  • Very slim and compact design with SMD technology

Here is the spec
310 Watts RMS continuous sine wave into 8 Ω
550 Watts RMS continuous sine wave into 4 Ω
860 Watts RMS short term sine wave into 2 Ω
The HPA-nxV500 is 2 Ω Stable
Biased into Class A/B
Power Bandwidth 3.5hz to 500khz -3dB
Slew Rate = 90 volts / microsecond approximately
Dampening Factor At 100hz 8Ω = 1300
Dampening Factor At 1khz 8Ω = 915
Dampening Factor At 10khz 8Ω = 248
RCA Single ended Input impedance 20kΩ
XLR Balanced Input Impedance 40kΩ
Differential Input Gain = 33.8dB
Single Ended Input Gain = 28.1dB
THD+N – Typically 0.005%
Recommended Voltage Supply +-78 volts DC

Having a nice amp will also need a nice chassis to go along. Here is want I found


Not bad erh!
It is actually a 4 channels amp to drive a stereo 4-ways speaker. The modules may be overkill, but what’s not in audiophile world? It keeps me happy, and that’s good enough!

Here are some more photos.


Tonight, I finally connected the amp and it is so impressive. Using active crossover certainly bring out all the details of music, the good and the bad. But this amp also bring out the smoothness and musicality of the recordings that I have. One of the advantage of this amp is that it is stable with 2 ohms impedance, this makes it a perfect match for ribbon drivers like Raven which can go down to 2 ohms at certainly frequency. RAAL is much better in that sense.


Regarding the sound, the highs are silky smooth with no harshness at all, without any caps on the input path, I get every single drop of music via this amp. It is a pure pleasure to hear the soprano to hit that high note without breaking. Just like the real thing in concert hall. Someone asked me if I worried about damaging the tweeter with DC output without a cap. Well, I do have a speaker protection circuit, and a pair of spare ribbon!

For the mid, the voice is very typical of AT driver which is rich and with high density, you can detect that with male vocal. The texture of all instrument in the orchestra can be clearly heard.

If you are looking for a DIY amp that is value for money, you cannot go far beyond NVX500! Oh, May be you can try NVX800!