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NDCX Discrete and NCDX Class D Amplifier modules

Ultra low 0.0003% typ distortion High End Class D Audio Amplifier modules

Test product for 30 days in your own system. Full money back warranty...

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Three different versions are offered. The Standard high value version NCDX, the buffer free version for surround sound and active filter setups, and lastly the high-end version NCDX-Discrete with a discrete buffer, built with discrete metal film resistors, and japanese audio grade transistors.
This Discrete buffer has shown superior performance over any ic-based OP-AMP we have used so far.

Technical Data

Output Power RMS250Watt 8 Ohms
Output Power RMS480Watt 4 Ohms
Output Power RMS480Watt 3.2 Ohms
Harmonic Distortion THD max0.003%@ 1 W 8 Ohms 50 - 20.000 Hz
Harmonic Distortion THD typ0.0003%@ 1 W 8 Ohms 1kHz
Harmonic Distortion THD typ0.005%@ 40 W 8 Ohms
Audio Bandwidth2 - 160.000 Hz@ 8 Ohms
Audio Bandwidth2 - 70.000 Hz@ 4 Ohms

The Discrete buffer is in charge of lifting the sonic performance of NCDX to new heights, for Class D technology, which is now comparable to even the best and most expensive factory power amplifiers in the world. If we should try to put words to the sound characteristics of these three different modules, the NCDX is the soft sounding version, a bit on the warm and dark side, if the differences are only minute. The NCDXi-627 has more air in the top, and more microprecision, and a more controlled bass. Both sound very clean, you can hear every detail in the recording. The NCDX Discrete has the most dynamic and open sound of the three, and also the most well defined and distinct bass reproduction. These are actually typical characteristics of discrete audio circuits compared to integrated OPAMP's.

The modules are tested, and ready built from us for your amplifier design. Add power, mounting base, signal, speakers and play!

The new bufferless version is intended for use in surround sound multichannel setups or active speaker setups. It does not have any buffer stage. This means it has a lower gain, only 22, compared to 50 for the standard version. Also it is always inverting, which can be counteracted simply by reversing the speaker wires. Lastly the power is limited to 200 W RMS in 8 Ohms or 4 Ohms, so no 480 W for this version. The benefit is lower idle consumption, so less heat, and also some circuit is removed from the signal path, which is always good for sound quality.

NCDXi-627 connection plan.

NCDXe-Discrete connection plan.


Here is all you need to build your own 2 x 400 Watt (4 Ohms) high end stereo amplifier, using the best parts:

2 NCDX modules.
1 Power Supply module.
4 Speaker binding post.
2 XLR or Phono plugs for input.
1-2 Meters of good speaker wire for hookup.
1-2 Meters of good (thin) signal wire for hookup.
1 Power Transformer 2x40V 800 VA.
1 optional Soft Start circuit.
1 Mains inlet with fuse.
1 Enclosure (with at least a little metal as cooling surface).

That's it! Now the great thing about DIY is you don't have to follow any specific recipe, you can build it exactly as you like. So for example you can go Dual Mono instead, then your checklist looks like this:

2 NCDX modules.
2 Power Supply module.
4 Speaker binding post.
2 XLR or Phono plugs for input.
1-2 Meters of good speaker wire for hookup.
1-2 Meters of good (thin) signal wire for hookup.
2 Power Transformer 2x40V 400 VA.
1 optional Soft Start circuit.
1 Mains inlet with fuse.
1 Enclosure (with at least a little metal as cooling surface).

You can also add a volume control to your setup if this interfaces better with your signal source.

Some of the above items you may have in your repository from previous projects, and these parts are great for reuse. The transformer does not have to be 2x40V, you can also use 2x33V, or even 2x24V, but the output power is reduced from 200W to 120W or 60W in 8 Ohms. Going the other way 2x45V or 2x50V is also usable, if you consider the allowable voltage on the main capacitors. For 63V caps, you should not exceed 42V transformer winding voltage. So with a 50V transformer you need to use 80 or 100V main caps. At 50V windings you get 480 Watts per channel in 4 Ohms of output power.

If you use our special silent ground power supplies with dual bridge rectifiers, you need to have a transformer with 4 secondary wires. This is standard for most torids, but some O or E core transformers only have 3 secondary wires. In this case it is not possible to use the dual bridge setup for silent ground. Then you have to use a classic power supply design with only one bridge.

NCDX has one of the lowest distortion figures in the world. Here recorded at 1Wrms in 4 Ohms, and with feedback loop set to 'pre' (before output inductor). Around 0.0007% THD from 20-20.000 Hz, (note the 20 Hz sample is a break-in sample) Typical value. Measurements on NCDXi-627 and NCDX Discrete have THD levels which are below our measurable limit of 0.0003%.

You might notice that the output inductor, if carefully designed adds no distortion to a Class D amplifier. The bandwidth is a full 1-125.000 Hz in 8 Ohms -6dB, which is adequate for the most demanding high end audio applications. (Or 200.000 Hz in 8 Ohms -6dB in Post mode).

NCDX is compatible with existing NewClassD fast recovery power supplies, and
has compatible gain, and same input/output connection setup with unbalanced and fully balanced input options. It requires a power supply of + - 58V to give 200 W rms in 8 Ohms, and also a gate drive voltage of ~20V, 200 mA is required.
NCDX will work perfectly with +/- 70V supply rail, giving extra power in 8 Ohms and up to 480 Watts RMS in 4 Ohms.

NCDX Versions

Three different wersions are offered, a standard high quality version NCDX, a high end version NCDXi-627 (using OPA627AU), and finally the new NCDX-Discrete with a discrete audio opamp. Note! The display option is no longer available, as the LCD part went out of production in summer of 2014.

Pre- and Post filter mode

Most Class D amplifiers operate in Post filter mode, meaning the feedback signal is taken after the output filter. This gives some advantages like frequency response is not or less dependent on the load impedance, and also in theory lower THD because the distortion of the output filter is compensated by the feedback loop. Other Class D amplifiers operate in Pre filter mode, meaning the feedback signal is taken before the output filter. This has other advantages, like the stability of the loop is not affected by capacitive loads, and the amplifier sounds more open.
NCDX offers you the possibility to chose either of these modes, as the only Class D amplifier on the market. By default it runs in Pre mode, because this usually sounds best, but you can change this simply by moving the solder bubble from the Pre pad to the Post pad. These pads are located close to the output terminals of the board.

Frequency Response

By October 2012 more than a thousand NCDX modules are operating all over the world.

Need to know installation info

You can find a complete installation guide, or as we call it a Cookbook for free download on the left hand menu buttons. However for quick reference here is a list of things you absolutely need to know before installing the NCDX modules.
Read all points before you turn on the power for the first time...

1..A Gate Voltage is required to drive the logic circuit on the module. This gate voltage should be 16-25V DC, with reference to V- (NOT GND!). V- is the -60V power rail, and the '-' of the rail voltage should be connected to this V-, and not GND. There is an on-board 7812 to regulate the gate voltage, so it does not have to be high prescision. So the total list of power supplies required are: +60V, -60V and 20V (over -60V) Vgate. The Vgate draws about 120 mA max. Vgate may be switched on and off with a low power switch or relay, while the module is in operation. The 60V's can also be anything from 33V to 68V.

2..If you are using low impedance loudspeakers, be sure to design the power supply accordingly. The power can be calculated as: (V+/1.4)^2 / R. So with 60V and 8 Ohms you get (60/1.41)^2 / 8 = 226 Watts RMS. With 2 Ohms you get 4 times as much, about 900 Watts. This will overload the module. Be sure to hit a maximum of 480 Watts RMS.

3..Do not modify the modules in any way. Do not submit them to extreme temperatures (below -10 Celcius or above 70 Celcius).

4..Mount the modules on a heat sink before connecting power. After switching power on, the first half hour keep attention on temperature of the module. It should not get warmer than it is comfortable to touch the heat block with your hand. Do not touch the components on the board while it's powered!

5..Be sure you connected V+ and V- right. Be sure you didn't rotate the power plug, it should only fit one way in the power supply and module. However if you are determined you can press it in the wrong way. V+ and V- are clearly marked on top of the board (maybe underneath the display).

6..Starting without load on input and output is now fully allowed. No problem.

7..Do Not use '- input' as GND. It should be obvious, however we still see many people making this mistake with disastrous result. You can connect '- input' to GND, but not use it as single GND or 'Cold' in an unbalanced signal chain.

8..If the module is very cold, wait 10 minutes before powering it on, dew can form on the module when going from cold to hot. Dew can kill the module.

9..Check the output terminals for shorts or leaks to the enclosure. Use a multimeter in Ohms position. Leaks can destroy the module.

10..Do not use very low impedance loads. Allowable limits to be determined. 3 Ohms and above is allowed at this point.

NewClassD ApS | DK7500 Holstebro | Denmark | tel +45 32130963 | E-Mail: |24016