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Messages - Tranquility Bass

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The Hypex NC502MP is the most powerful amplifier used in the Ultimate Amplifier and represents the first two channels (1-2) out of the 8-channels of amplification. Typically it would be used to drive the woofers in a stereo active speaker system so it is imperative that it does this without any problems. With a name plate power rating of at least 500 and 350 watts per channel into 4 and 8 ohms respectively the measurements we made did not disappoint. The following measurements were made using the dScope III by sweeping the power from 10mW to beyond clipping and plotting the THD at 1kHz. The maximum power output is measured at 1% THD @ 1kHz the same as in the Hypex data sheet. The results show that the 4 ohm single channel measurements of 750 watts @ 1% THD showed that the manufacturers power rating is very conservative for these modules. Also there is doubling of power from 8 ohms to 4 ohms which shows that the switch-mode power supplies are extremely well regulated which is a testament to whoever designed the power supplies ! The low actual distortion measurements also confirm the measurements presented in the manufacturers datasheets for this module ;)

Hypex NC502MP THD+N vs Power @ 1kHz into 4 ohms, Single Channel Driven

Hypex NC502MP Power at 1%THD @ 1kHz into 4 ohms, Single Channel Driven

Hypex NC502MP THD+N vs Power @ 1kHz into 8 ohms, Single Channel Driven

Hypex NC502MP Power at 1%THD @ 1kHz into 8 ohms, Single Channel Driven

Performance and Measurements / Re: Measurement Equipment
« on: August 08, 2020, 09:06:25 AM »
To measure class-D amps using an audio analyzer with digital processing it is prudent to filter out any ultrasonic carrier noise (300kHz and above) as this can fold back into the audio spectrum and interfere with the measurements by exaggerating the noise measurements even though the noise is not part of the audible spectrum and for all intents and purposes is essentially filtered out by the speakers and certainly cannot be heard by the ear !.

Both Prism Measurements and Audio Precision sell outboard filters designed for this very purpose however we decided to build our own based on Prism's own specs which is very similar to a Chebychev 3rd order low pass filter with a 0.05dB equi-ripple response in audio pass-band and at least 50 dB attenuation at 200kHz.

Our filter design yields a very similar response ;)

The first incarnation resulted in a 1dB drop at 20KHz :(

For some reason the calculated values for the components was yielding an attenuation of nearly 1dB at 20KHz but with some experimentation with the simulator a better match was obtained and now the filter is within 0.05dB from 20-20KHz

Performance and Measurements / Measurement Equipment
« on: August 08, 2020, 05:36:55 AM »
Measurements are done with a variety of instruments namely :-

Prism dScope III Audio Analyzer,
Custom designed LPF for measurement of class-D amplifiers similar to Prism ds-LPF
Agilent 34401A 6.5 digit Digital Multi-meter
Tektronix Digital Oscilloscope models, TDS784A, TDS3012, TDS7054
Tektronix CRO model 2246A
Leader LDC-824 6.5 digit 500MHz Frequency Counter with Oven Controlled crystal oscillator
E-MU 0404 external 24 bit 192KHz sound card

Ultimate-Amplifier by Analog-Precision / Thermal Management
« on: August 07, 2020, 11:14:29 AM »
Although one of the benefits of class-D amplifiers that has been touted for so long is efficiency, in practice the amps can still generate a sufficient amount of heat and the switch-mode power supplies also contribute to this heat. The Hypex NCore amps are no exception. A look at the data sheet shows that for the NC502MP producing 400 watts a channel into 4 ohms the amps will dissipate about 200 watts which equates to around 80% efficiency. Whilst this looks good on paper, 200 watts of power dissipation will quickly raise the temperature of the small plate heat-sink on the amp module to unsafe levels unless this heat can be channeled away quickly. Then there is the question of dealing with 3 more stereo amps for a total channel count of eight amps each dissipating a given amount of power depending on the frequency response and program content. Although the power output of the amps should diminish the higher the frequency range they are ask to handle, the thermal requirements should not be assumed to be negligible. This a mistake many people make with class-D amps by mounting them on a thread-bare chassis with minimal thermal capacity thus questioning the long-term reliability of the design as a whole.

Our custom designed case works exceptionally well at dissipating huge amounts of thermal energy away from the amp. All of the amps are mounted on a 10 mm thick aluminium heat spreading plate with a large surface area the size of the bottom of the case. This acts as a transient thermal sink with a huge thermal capacity and which can sink a huge amount of transient energy without raising the temperature quickly to unsafe levels. Then the wrap around case with a large amount of surface area acts to slowly dissipate away this energy using convection.

Add to this is our thermal management system which monitors and reports temperature extremes on a channel by channel basis whilst maintaining temperatures inside the case at safe levels.  We deploy a 60mm fan chosen for its low noise level along with a dedicated fan controller which employ both a fan and thermal closed loop control system which carefully ramps up the fan speed over a range of temperatures in order to keep the temperature of the system at a sustainable level and without generating intrusive noise.

The firmware has a diagnostic mode which can continually report the amplifier status over a serial port, including temperatures and fan speed. We can see the first two channels are working hard because the on-board thermistors are reporting higher temperatures than the other channels which are sitting idle. The last two channels are not showing anything because the HF100 modules do not include the thermistors. The temperature of the heat spreading plate has risen to 34 degrees and the fan has already spun up to 1500 RPM to get rid of any excess heat inside the case.  If the thermistor temperature rises to 80 degrees C the respective channel indicator LED will turn white. Further increases above 90 degrees will shut down the amplifier until the temperature is reduced to 80 degrees.

Performance and Measurements / Re: Measurements
« on: August 05, 2020, 05:58:47 AM »
Testing the clipping indicators. The Hypex amplifier modules can assert their channel clipping flag if the output of the amplifier exceeds either a set voltage or current limit. The clipping flag from the Hypex amplifiers are non-latched which means we need to latch the clipping flags in hardware otherwise the software could miss it if it is relying on polling. As a result each channel can report the clipping status in real time by making the LED turn red for at least 100mS so it can't possibly be missed by the user. This tells the user that amplifier is being over driven and the level should be reduced !

Scope image of the first two channels of the amplifier being driven into voltage clipping.

Indicator LEDs turn red when its respective channel is being over-driven into clipping thus signalling to the user to reduce the level !

Performance and Measurements / Scope Measurements
« on: August 01, 2020, 02:40:30 AM »
Some simple power measurements on the Ultimate Amplifier using a scope. The first two channels are powered by a Hypex NCore NC502MP amplifier module which would typically be assigned to the low frequency channels in an active speaker system. This is the most powerful of all amplifiers in the Ultimate Amplifier with a name plate rating of 500 watts per channel into 4 ohms. We used the channel clipping indicators to determine the maximum power threshold before clipping but later on we will use the dScope III audio analyzer to accurately measure the power output at a given THD level and show how conservatively rated these amps really are ;) The results will shock you at how powerful these amps really are and how well designed the switch mode power supplies are to maintain tight regulation and almost doubling power into 4 ohms ;)

Continuous 1KHz Sinewave into 4 ohms before clipping with one channel driven corresponding to 595 watts into 4 ohms.

Continuous 1KHz Sinewave into 8 ohms before clipping with both channels driven corresponding to 321 and 317 watts respectively.

Full Power 20Hz Tone-burst with 1 to 5 duty-cycle (5 cycle on 20 cycle off) single channel into 4 ohms

Full Power 100Hz Tone-burst with 1 to 5 duty-cycle (5 cycle on 20 cycle off) single channel into 4 ohms

Full Power 1000Hz Tone-burst with 1 to 5 duty-cycle (5 cycle on 20 cycle off) single channel into 4 ohms

Top Trace = Full Power 100Hz Tone-burst with 1 to 5 duty cycle with 5 cycle on 20 cycle off single channel into 4 ohms
Bottom Trace = Current measurement of voltage across a 0.1 ohm sense resistor (20 amps per division)

Full Power 1000Hz Tone-burst with 1 to 5 duty-cycle (5 cycle on 20 cycle off) single channel into 8 ohms

Continuous Sinewave at 1000Hz After Clipping with both channels driven into 8 ohms

Green lights mean all channels are go ! What do you do in lockdown whilst waiting for Ultimate-Preamp DSP boards to be manufactured by our production house ? Answer is to write an operating system for our multi-channel power amp. This time we are cutting code for an STM32 M3 ARM micro and not a SHARC DSP. So far everything is going to plan.

  • Power Amp Mains Sequencing tick !
  • Main-switch and trigger-IO monitoring and relaying   tick !
  • LED display driver tick !
  • Real-time Amplifier/clipping/DC error/Over-Temp-Alarm and general fault monitoring and display tick !
  • Thermal management in testing phase !

The custom all stainless steel case is earmarked for a customer who along with the still to be delivered Ultimate Preamp Plus (sorry for the delays) will be using it in a custom active speaker system of their own design. Using all Hypex NCore amplifier modules in a custom case that matches the Preamp we found the Hypex modules to be the ideal choice for this application with no shortage of power and performance.

Feature Requests / Re: Network Connection / Roon Support
« on: July 25, 2020, 01:38:08 PM »
To implement this on our hardware we would have to steal away potential DSP resources that could be used for normal DSP processing ! Can you use daphile as a Roon Endpoint ?? Because if you can it is free software that can run on any PC hardware ;)


Ultimate-Amplifier by Analog-Precision / Coming along nicely !
« on: July 15, 2020, 03:01:25 AM »
The wiring looms require some thought as you don't really want to mix up the high current mains and speaker wiring with the sensitive small signal wiring ;)

Ultimate-Amplifier by Analog-Precision / Some assembly required !
« on: July 15, 2020, 02:58:49 AM »
Yes lots of assembly required !

Ultimate-Amplifier by Analog-Precision / Parts arrivethed !
« on: July 15, 2020, 02:46:10 AM »
Nice little package from Mouser arrived !


Ultimate-Amplifier by Analog-Precision / The amplifier modules.
« on: July 15, 2020, 01:01:49 AM »
The Hypex Ncore amplifier modules used in this build consist of:-

1 x NC502MP
2 x NC252MP
2 x HF100


Feature Requests / Re: Phono input
« on: June 18, 2020, 09:45:54 AM »

Request for a switch to reverse polarity for the single LP

Request  to modify via software the gain of the first stage

Request  to modify the complete RIAA to an incomplete  RIAA without the 75μS (2122Hz) turnover frequency

Many thanks


Thanks Alberto

We can add those features and even have a user customizable RIAA curve as well as the industry standard ones ;)


Zee boards have arrivethed !

A present from DHL ;) Partially assembled boards from our prototype assembly service. The rest of the assembly to be done by yours truly  :-X


News Updates / New test equipment for the lab
« on: June 12, 2020, 04:28:54 AM »
We are always on the lookout for new and useful test equipment to add to our lab, and one of the things we have always wanted was a decent audio analyser. Although we have a couple of external sound cards which have been quite useful, nothing beats a dedicated audio analyzer, so when a Prism dScope III came along at the right price we jumped at the chance and purchased it. The Audio-Precision APx555 at $28,000 USD was way out of our budget and save for a few dB less dynamic range, in terms of over all features and customization, the dScope III offers everything we need a plus a whole lot more. We have already used it to chase down a few illusive issues in our existing preamp design and incorporated the changes in our new Preamp designs. Such is the benefit of having access to the right test gear ;)

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