We are excited about the release of this amp. It has been under construction for a long time and we have put a lot of effort into finding optimum solutions throughout the amplifier. We do not believe in snake oil theories or old audiophile myths and there is nothing mystical going on here. Just hardcore engineering using the best components available today.
Our goal is a lot of power, compact design, a clean look with no visible screws or seams, low noise, high CMRR and low THD+N. We are confident this is a well engineered product that will last for many years.
We also want to be transparent and privide ALL measurements and technical information about the product.
A lot of power combined with compact design without compromising on life expectancy due to raised temperatures was a challenge and it became early clear that this is only acheivable by introducing fans.
Fans are often frown upon in in Hi-Fi communities. Who wants an amp with noisy fans that wear out and needs servicing every second year?
After testing many fan solutions we landed on two Noctua NF-A6x25 4-pins with PWM speed control. These fans can operate down to 300RPM and are
truly 100% silent up to 1000RPM. At 1600RPM the noise is 8,2dB(A) according to Noctua.
https://noctua.at/en/nf-a6x25-flx/specification
The fan tunnels are designed with unequal length to avoid amplification of coinciding frequencies if run at higher RPMs. It is impossible for the fans to create any vibration in the cabinet since it is milled out of a massive aluminium block and the fan tunnels are in fact several centimeters thick. To further safeguard from any possible vibrations they are decoupled from the chassis using rubber mounting screws.
The fans are controlled using intelligent fan control software that monitors how the user uses the amplifier and how high the environmental temperature is. The input to the intelligent fan control is taken from three temperature sensors. One inside the cabinet and one mounted on each output coil.
As long as the temperature is under a certain limit the fans will not start at all.
I have run torture tests of the amp at 1200W RMS continous into 8 ohms for two hours straight (a sine wave) and the fans kept the temperature under control when running at 2000RPM. While not truly silent anymore the sound emitted is well damped and really not noticable at a couple of meters distance. 1200W RMS sine wave has a crest factor of 3dB and is an impossible music signal. A music signal has almost allways a crest factor of more than 12dB and even when playing music with 1300W RMS in peaks (140V peak voltage) the fans will operate below a truly silent 1000RPM. And to be frank, at those levels it does not really matter anymore...
This a picture picture of the amplifier after two hours of torture. The hottest external temperature was 58 degrees and the hottest internal part was 79 degrees. I measured on 13 different locations inside the cabinet during the test. In the background we can see my dummy load dissipating 1200W of power.
No electronic device should not be left on when not in use. This also applies to Class D amplifiers and contradictory to old Hi-Fi myths this amplifier actually measures slightly better when cold. There is no gain in sound quality by leaving it on, and to have the longest life expectancy from the product we strongly advice to turn the amplifier off using the front panel button when not in use. The power supply and the NC500 modules are then shut down and only the microcontroller and front LED is active. These are powered from an extremely power effective small SMPS power supply using only about 0.25W.
The intelligent fan control allow for a certain raise in the temperature the first 48 hours of use without starting the fans at all if the environmental temperature is less than 30 degrees celsius. If the user decides to leave the amp on continously the fans will start a more active state and will activate at about 500RPM to make sure the temperature of the NC500 modules are held at low levels. All this ensures a long life of the product regardless of the use, environmental temperature or power delivery without compromising at all on the noise. Worst possible life expectancy is calculated to 15 years if used 6 hours a day every day.
The fans have a MTBF of 150.000 hours (17 years) at full speed so this should not really be a problem either.
The fan filters are attached using magnets and are easily removed and re-attached if cleaning is neccessary. They are prduced by Demciflex and are a quality product with high air flow and are easly rinsed.
https://www.demcifilter.com/how-it-works-2
The fans air flow is concentrated around the hottest parts of the amplifier with 3D printed fan ducts. This enables even very moderate air flow to be effective. Nothing more to them than that.
The air exhaust is in front bottom of the cabinet through generously sized holes. When the fans are
not active there is a moderate natural convection cooling effect from the air going the opposite direction and exiting through the fans.
Both fans RPM are individually monitored by the microcontroller. If a fan fails to maintain it's correct RPM this will be indicated on the front LED with RED flashes.
This is the MCU card.
With the DIP switches OPT1 and OPT2 is is possible to choose from four different fan "profiles"
1. "SILENT". In this mode slightly elevated temperatures are allowed before the fans increase speed. Of course at the expense of slightly increased temperatures and life expectancy. Otherwise equal to default.
2. "DEFAULT". The recommended setting ensuring silent operation under all normal conditions.
3. "COOL". In this mode the fans will increase RPM at a slightly lower temperature than default. Otherwise equal to default.
4. "POWER" This mode is intended for use in installations with elevated temperatures or in installations with high power requirement and where fan noise is not an issue. The fans are still intelligent and will not run at higher speed than neccessary, but main focus here is adequate cooling from the second it is turned on. The fans are allowed to speed up to their maximum 3000RPM and will keep the amplifier cool under ANY circumstance.
We are using the SMPS3kA700 PSU. We started with two SMPS1200 PSU's but we were not happy with the heat generated in the transformers. When driven hard the temperature reached 120 degrees! The SMPS3kA is surprisingly much better and the hottest spot on the transformer reaches only 88 degrees under same conditions. In fact the SMPS3K is about 50% more powerful than two SMPS1200s.
3D printed parts are used many places in the amplifier. We use high temperature resistant PETG plastic. For instance is the input buffer card and the XLR connectors in the back fastened using only two specially modelled plastic pieces. No screws
The microcontroller is a AVR MEGA 2560. Not the most powerful MCU, but it has a lot of I/O for everthing we measure throughout the amplifer. More about this later.
About the unisolated speaker leadout: Nicely spotted
This is a part of the optimization of the feedback system in bridged mode.
Nobody mentioned the aluminum cooling bar?
This cooling bar lowers the temperature on the NC500's coils by 15 degrees celcius.
Heat is transported away from the output coils and into the massive cabinet through the cable channel. Some heat is also transported down to the bottom lid through the alumunum spring that keeps this cooling bar securly in place. This arrangement gives us probably the coolest running NC500's in the market. At least NC500's capable of the same or near the same power output.
Since we are in the technical corner I want to talk a little about the things we measure and control using the microcontroller (MCU).
It continuously measures the status of the NC500 modules and the SMPS power supply.
* Speaker output current (up to 25A).
* NC500 overcurrent conditions individually on both channels (500.000 times per second).
* NC500 signal clipping individually on both channels (up to 20kHz).
* NC500 error status signal from both modules.
* SMPS rail voltages.
* SMPS error status.
These signals are used to give the user information on the front panel RGB LED. Different colours and combination of colours will inform the user if the output is overloaded. Both overcurrent conditions and clipping conditions are reported individually for both channels through different colour combination. The user can then easily indentify if the clipping is due to too high current or too high voltage and if this occurs on left, right or both channels.
It can also mute the two channels. This is important in bridged mode. If one channel fails, the other have to be muted very fast to avoid damage to connected speakers. Much faster than just disabling the SMPS and just wating for the SMPS filter caps to discharge.
Other jobs for the MCU is of course the operation of the front RGB LED, the fans, the on/off button and the on/off of the SMPS.
If you are interested I can talk a little about the design of the input buffer also. But that is for another day.
