I've had some time now to listen to it in the main system which uses a Sony CDP990, AudioSector NOS DAC, AKSA GK-1 SS section (no tubes), floor standing speakers using Scan Speak 18W/8531G00 & S2905/970000 drivers. 

The first impression is one of overall smoothness without a hint of harshness. Female vocals do not have any edginess and remain controlled at all times as do other instruments in the Mid’s. Top End has a nice quality but misses that last amount of shimmer.... only a very small amount but noticeable.

The stereo image is very good and there is depth appearing in the sound stage .

The vocals and instruments are well defined.

The bass has good tonal quality and is very powerful and maybe too much so for my system. but I did extend the speaker ports as an experiment and the bass became neutral and tonally balanced so it is just a matter of retuning the speaker to suit.

Overall, I'd say the sound is very accurate but I miss that extra charm, induced by H2 harmonics. The NX150 would kick a lot of commercial amps out of the way easily such as a Rotel I recently had.

I could easily live with the NX150, it is a Fine Amplifier.

The instructions are good for an experienced builder but maybe might need a few extra bits that we take for granted for the non experienced, such as heat sink mounting with Mica washers, checking for shorts onto the heat sink etc.  

I'm looking at this amp in a very critical view considering the equipment that is out there and has to compete with plus I've had over 35 years in this game and have my own listening idiosyncrasies.

Peter (aka rabbitz:DIYaudio.com)

www.RZaudio.com

Specifications   

+-56vdc Voltage Rails (Idle, No Signal)

146 Watts RMS into 8 Ohms

230 Watts RMS into 4 Ohms

+-63vdc Voltage Rails (Idle, No Signal)

185 Watts RMS into 8 Ohms

275 Watts RMS into 4 Ohms

Frequency Response: 2hz to 160khz (Input Filter Limited)

Power Bandwidth 2Hz - 500khz -3dB Filter Limited

THD Typically 0.05% @ 8 Ohms 1khz

Damping Factor 400

Input Impedance 34k Ohms

Input sensitivity for full power out into 8 Ohm load 900mv 

Features of the New NX150 Amplifier are....

• Fully Symmetrical Double Differential Input Stage

• All Hexfet Differential Input Stage    

• Fully Symmetrical Topology

• Bipolar VAS HEXFET Cascoded Driver Stage

• 4 x Single or Dual Die Lateral MOSFET O/P Stage

• HEXFET Constant Current Sources

• Very Low  Distortion

• Compact PCB measures only 100mm x 50mm

• Plated Through Holes, Solder Masked

• Double Sided and Screen Printed PCB 

• 3 Ounce Copper Foil on both sides of the PCB

• No Cross Conduction Problems 

• (Zero Cross Conduction @ 100khz)

This Topology I believe gives the best of both worlds.

The excellent sound one gets from an all Hexfet and Lateral gain stages as well a small signal Very High Gain Bipolar Voltage Amplification, then matched to a Hexfet Cascode Stage, which buffers the Bipolar VAS and goes on to drive the Lateral MOSFET output stage.

The performance is really something else, very high power bandwidth with the smoothness and detail of Hexfets and Lateral Fets. 

I will be releasing at a later date a Hexfet output stage version of this design.

This NX150 employs a new driver technology that totally eliminates overheating of the output stage, so much so that even at 100khz the output stage MOSFET's remain at the same temperature as if they were operating at 1khz.

Most amplifiers operating at 20khz with no load will over heat the output stage under these conditions, the NX150 remains cold at 100khz.

This translates into unsurpassed imaging and detail, not heard from most of the audio amplifiers on the world market today.

Not only that but the extra power that is available from the power supply, because it is not been used to over come the excessive heating of the output stage allows the NX150 to have the most effortless sound quality, even with just a modest 300VA toroidal transformer powering both channels at the same time.

Here shown below is some output waveforms from the NX150, showing excellent clipping behaviour and Very Wide Power Bandwidth.

1khz Sine Wave in Hard Clipping 

10khz Sine Wave in Hard Clipping 

Power Supply Requirements

The NX150 will operate on supply voltages as low as +-20 volts very well 

and as high as +-70volts

Recommended Supply Specifications

+-56vdc Voltage Rails

146 Watts RMS into 8 Ohms

230 Watts RMS into 4 Ohms

1 x 300VA toroidal transformer with 2 x 40 Vac secondary windings. +-56 Volt Rails (Idle)

Minimum 2 x 10,000uf 80v filter caps required

Or PSU-Two Power Supply Unit

1 x MDA3504 Bridge Rectifier

For Dual Channel  Stereo 

400-500VA Toroidal Transformer 

+-63vdc Voltage Rails

185 Watts RMS into 8 Ohms

275 Watts RMS into 4 Ohms

1 x 400VA toroidal transformer with 2 x 45 Vac secondary windings. +-63 Volt Rails (Idle)

Minimum 2 x 10,000uf 80v filter caps required

Or PSU-Two Power Supply Unit

1 x MDA3504 Bridge Rectifier

For Dual Channel  Stereo 

500-625VA Toroidal Transformer 

What do you need to Complete a Stereo NX150 Amplifier

• 2 x NX150 Amplifier Module Kits

• 1 x PSU-Two Power Supply Unit 

• 1 x 300-400VA Toroidal Transformer

• 2 x Conrad MF30-100 Heat Sinks

• 1 x Mains Rated Power Switch

• Power & Signal Cabling

• 2 x RCA Input Connectors

• 2 x Speaker Binding Posts

• Plus other small misc, hardware