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Topics - Tranquility Bass

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46
Introduction:

The Ultimate Preamplifier features a magnetic cartridge input that also incorporates the requisite inverse RIAA equalization curve. The phono amplification stage is a hybrid design and is a mixture of both analog and digital gain cells along with the inverse RIAA curve implemented in the digital domain exclusively by the DSP. This makes its frequency response extremely accurate to within 0.1dB with no inherent drift over time. What we are looking at when we measure the frequency response of the Phono stage should look something like this from  WikiPedia .



Conclusions:

The frequency response measurement of both channels of the Inverse RIAA response as implemented in the Ultimate Preamplifier shows a text book response with both channels displaying identical responses as you would expect from the accuracy of the digital domain ;)

47
Performance and Measurements / ADC frequency response
« on: August 30, 2020, 11:33:27 AM »
Test Methodology:

In this test we exclusively test the frequency response of the ADC by not including the the DAC in the measurements. We do this ny measuring the ADC output from an S/PDIF serial stream generated by the Preamp which we then feed directly into the digital input of the dScope. Since the Preamp samples at 192kHz by default. the Toslink output of the Preamp will not handle anything above 96kHz so we have to use the Coax out for this test. NB it is possible to switch the preamp into sampling at 48 or 96 kHz but by default the Preamp is shipped at its highest sampling rate so we use this for the test.

dScope Analog Output -> UP Analog Input

UP S/PDIF or Toslink output -> dScope S/PDIF or Tosiink Input

Conclusions:

Only 0.3dB down at 20Hz !!

48
Performance and Measurements / DAC - Jitter Tests
« on: August 30, 2020, 11:06:09 AM »
Test Methodology:

There are a variety ways of measuring jitter but the single single RMS or peak jitter metric is not very revealing since it does not reveal the nature of the jitter, so a more detailed analysis such as the J-test method is used to test the susceptibility and tolerance of the device under test. The J-test methodology is described on the ASR forum J-test methodology 1 and J-test methodology 2

Test Results:


Conclusion:

As one can see from the detailed spectra in the following tests any side bands from the J-test are buried way into the noise floor below the threshold of hearing and should not pose any audible issues at all ! In fact, because all three test results are very similar it is possible that we are measuring the jitter of the analyzer itself !! All in all an exceptional result and shows the effectiveness of the high quality oscillator used, the clock distribution network, the jitter reduction hardware in the Sabre DAC as well as the careful attention to detail that we placed in the design of the DAC and pcb layout ;)

Compared with the DEQX Pre-mate as measured by Stereophile we can see that the Ultimate-Preamplifier indeed has way superior jitter performance ;)


49
Performance and Measurements / dScope III Performance Upgrade
« on: August 28, 2020, 06:14:00 AM »
This thread is about improving the performance of an already great bit of test gear. If you don't have the necessary skills to do these mods or your instrument is still under manufacturers warranty then we don't suggest you perform these mods.

According to the specs the Prism dScopeIII has an equivalent input noise voltage of about 1.2uV which is equivalent to about -116dBu and which was also confirmed by NewAvGuy on his blog. We also confirmed this on our own dScope III by running a similar test by shorting the inputs and measuring the noise level over a 20kHz bandwidth and we also got close to -116 dBu which is only a few dB lower than the Audio-Precision analyzers which sell for a lot more than the dScope III ;)



Is it possible to improve on this ? The ADC converter use in the dScopeIII is a AKM AK5394A which has a S/N 123dB so there should be some room for improvement. Removing the top cover of the dScope III reveals that all of the ADC and DAC circuitry is contained on a riser board that plugs into the switched attenuator board. On further observation we note some of the IC's are plugged into sockets which would indicate that the manufacturer was contemplating replacing the chips with better devices as they became available or simply they may have been trying different chips from a batch until they found the ones that met their specs. Bear in mind the design of this analyzer dates back to 2001 so it is quite remarkable that they were able to achieve these specs with the silicon they had at the time ! We note that the two IC's closest to the ADC are standard NE5532 dual opamps which would be part of the buffers/level-shifters used to drive the ADC. As these devices have an equivalent noise voltage of 5nV/rtHz it would be a simple exercise to replace these with devices with better noise an distortion performance. As high quality opamps with DIP packaging are slim pickings these days we ended using the tried and true LME49720 which is a drop in replacement with much improved characteristics over the venerable NE5532. The LME49720 has an equivalent noise voltage of 2.7nV/rtHz and an order of magnitude lower distortion so we could expect at most an improvement of noise reduction of 5.35dB but in reality it would be somewhat less. Lets see what happens ;)



And from the new noise measurements we see an improvement of about 3dB from -116dBu down to -119dBu so well worth the few dollar investment of these opamps ;) The question arises could we improve on this yet again ? Since the DIP style of package is becoming very rare for audio opamps, to get a lower noise floor in a dual opamp configuration would mean that we'd have to go to an SMD package and use some sort of SMD to DIP adapter so probably not worth it for chasing down a few extra dB's. Maybe an experiment for a rainy day but the current mod is quite easy to achieve for an hours work and a few extra dollars for the opamps ;)




50
Performance and Measurements / DAC - THD + Noise @ 1kHz
« on: August 28, 2020, 02:58:04 AM »
Test Results:


Conclusions:

The Ultimate-Preamp 2/+ has vanishing low levels of distortion and noise, so much so that it is approaching the limits of our dScope III audio analyzer and most likely exceeding it !! Even at much higher output voltages compared to your typical DAC the UP2/+ does not disappoint as shown by the following screen shots of the THD+N measurements 😁 The difference in distortion between the two channels is most likely due to the differences in the analyzer ADC and not the Preamp because reversing the channels does not appear to have any effect on this 😉 To get better measurements we would need access to an analyzer such as the Audio Precision APx555 which nulls out the fundamental so that it can more accurately read the harmonics from the output of the Preamp rather than the added distortion from its own ADC. However, we are not complaining about these results because it looks like all of the work we have done on the DAC and post DAC circuitry in this new Preamp has payed off

The THD + Noise performance of the unbalanced output is a whisker higher than the balanced output but still does not disappoint ! Below 1kHz one can clearly see the mains artifacts that are not present in the balanced output spectrum but are still buried way down below the threshold of hearing of -120dB and so of no concern !! These artifacts are caused by leakage flux from the transformer used in the linear power supply setting up earth loops in the internal wiring from the DSP board to the Unbalanced output board. Yes folks, balanced always wins out simply because common mode noise is cancelled out !! Above the 1kHz fundamental test signal we can see the usual harmonic distortion spikes mainly attributable to the distortion of the ADC used inside the analyzer. There are no spurious noise spikes from an external switch mode power suppliy simply because we don't use one and the on-board switching regulator used to power all of the digital circuitry runs at 500kHz which is well outside the audio bandwidth !

51
Performance and Measurements / Noise Performance (No Signal)
« on: August 28, 2020, 01:20:08 AM »
Test Results:


Conclusions:

The noise floor of the balanced output of the UP/2+ is only 6dB above the noise floor of the dScope III audio analyzer which is approaching -116dBu or 1.2uV  RMS ! Bear in mind that unlike standard DACs we have incorporated a buffer amplifier on each balanced output to boost the output level from the output of the IV converters which will of course add some additional noise of its own. Also in the 2nd image capture below we have expanded the frequency axis from 0-1kHz to show the almost non existent mains components sitting above the noise floor which is a tribute to the balanced design.

The noise performance of the unbalanced output is slightly higher than the balanced out but still does not disappoint ! On the expanded frequency scale one can clearly see the mains artifacts that are not present in the balanced spectrum but are still buried way down below 120dB !! This is caused by leakage flux from the transformer setting up earth loops in the internal wiring from the DSP board to the Unbalanced output board. Yes folks balanced always wins out simply because common mode noise is cancelled out !!

dScope III Noise Performance:

  • Unmodified dScope III Noise with inputs shorted



  • Upgraded dScope III Noise with inputs shorted



  • Upgraded dScope III Noise with inputs shorted (A-weighted)






52
Performance and Measurements / Measurement Equipment
« on: August 28, 2020, 01:13:06 AM »
Measurements are done with a variety of instruments namely :-

  • Prism dScope III Audio Analyzer,
  • Agilent 34401A 6.5 digit Precision Digital Multi-meter
  • Tektronix Digital Oscilloscope models, TDS784A, TDS3052, TDS7054
  • Tektronix CRO model 2246A
  • Tektronix Arbitrary Function Generator model AFG310
  • Hewlett Packard AC RMS Voltmeter model 3400A
  • Leader LDC-824 6.5 digit 500MHz Frequency Counter with Oven Controlled crystal oscillator

References:







53
And now for the Hypex NC252MP Ncore power amp measurements. The Ultimate amplifier uses two of these modules to give 4 channels of additional amplification. The name plate rating of these amps are 250 and 200 watts into 4 and 8 ohms respectively @1% THD. We measured the power to be 306 and 159 watts into 4 ohms and 8 ohms respectively at 1kHz and 1% THD. Whilst the 8 ohm power measurement is down on the manufacturers name plate rating the doubling down of power into 4 ohms shows how well regulated the switch mode power supplies are.  ;)

Hypex NC252MP THD+N vs Power @ 1kHz into 4 ohms, Single Channel Driven



Hypex NC252MP Power at 1%THD @ 1kHz into 4 ohms, Single Channel Driven



Hypex NC252MP THD+N vs Power @ 1kHz into 8 ohms, Single Channel Driven



Hypex NC252MP Power at 1%THD @ 1kHz into 8 ohms, Single Channel Driven


 

54
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




55
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




56
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.





57
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


58
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

Cheers
David






59
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 ;)



60
Ultimate-Amplifier by Analog-Precision / Please Read !
« on: June 10, 2020, 10:21:50 AM »
Please use this forum to discuss anything regarding the Analog-Precision Ultimate-Amplifier.

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