Topics

Note: The following is a mailing list posting by John Dunlavy, a well known audio designer. I stashed a copy of this posting because I wanted to cite it in my stereo equipment page, and at the time there were no good repository of the mailing list or usenet articles that was accessible via a stable URL. I would suggest you check out audio postings by dunlavy for even more information.

96.11.5 - Cable Nonsense - Long.pdf

A white paper on the performance attributes of various loudspeaker designs.

CONES, PLANARS & DOMES.pdf

LISTENING ROOM CONSIDERATIONS.pdf

Various Measurements used by Dunlavy

Step response.pdf

Competitor Impulse Responses

BKn competitor impulses YUK.pdf 

Click here to view John Dunlavy's CV

https://audiokarma.org/forums/index.php?threads/dunlavy-audio-labs-archive-from-the-mind-of-a-legend.769216/

https://forum.polkaudio.com/discussion/65807/worlds-most-accurate-loudspeaker/p2

https://www.audiosciencereview.com/forum/index.php?threads/the-dunlavy-interview-1996.14646/

https://www.diyaudio.com/community/threads/designing-creating-a-dunlavy-type-speaker-from-the-ground-up.368244/

https://tmraudio.com/blog/duntech-to-dunlavy-legend-with-a-colorado-connection/



Loudspeaker Measurements

Quality Control Program at DAL

DAL's listening rooms

Tech Talk

Since our original facebook page was hacked we were never able to recover the ability to login no matter what we did so we gave up on it. Since then facebook has upgraded its security with 2FA so it is harder for hackers to do this.

Anyway, rather than keep hitting our heads against a brickwall trying to recover the unrecoverable I have created a new facebook page at https://www.facebook.com/NewAnalogPrecision

And for those playing along at home the old facebook page is still accessible

https://www.facebook.com/AnalogPrecision/

On the drawing board is our next Revision(D) of the main DSP board which now features an upgraded ADC (Analog to Digital Converter) from the existing 24 bit TI part to the Flagship ES9822PRO 32 bit ESSTech ADC. The ES9822PRO ADC features ESS proprietary Hyperstream II ADC Architecture, which delivers unprecedented conversion performance and yields top notch specs of 124 dB DNR and -117 dB THD+Noise. The ES9822PRO has an Ultra-Low Noise Floor Bandwidth of 200kHz. This bandwidth is up to 10 times wider than the competition, enabling higher resolution at higher sampling rates and along with the ESS 8-channel ES9038PRO Sabre DAC and our own onboard FEMTO master clock providing infinitesimal jitter we are certain this should satisfy the most fastidious analog aficionados who are into vinyl or reel-to-reel playback ! 

[These preamps operate in perfect sync with each other and the master preamp controls the volume, balance and muting on all of the other slave preamps in perfect unison.]

We had a recent enquiry by someone who wanted us to build a preamp with 16 outputs ! But what if someone asked us to build a 24 or 32 or even a 48 channel or more hi-end stereo pre-amp and our preamp only had 8 outputs? Fear not with the external Link-Port on both the UP2 and UPP you can chain as many preamps together as you need to get as many outputs as you need with no loss of information or performance ! Why would you need such high channel count ? One application comes to mind and that is a phased array loudspeaker or wave shaped loudspeaker with many independent driver channels such as the B&O kii audio etc or even a multiple active speaker that are all controlled by the same pre-amp.

By itself the Ultimate Preamp 2/+ has 8 outputs plus an optional digital output to drive an external stereo DAC bringing the total output count to 10 channels which is still far short of 48 channels. However, the main DSP board used in the preamp has provision for connecting multiple DSP boards as a master and many slave arrangement in the one chassis using the on-board Link-Port connector.

However, from a practical point of view this would require a redesign of the enclosure and power supply to handle multiple boards and output connectors which is just not practical at this point in time. We just needed to extend this facility outside the chassis so that we could link multiple preamps in 8-output clusters and they all needed to sync perfectly together when changing things like the volume, balance, mute etc because you don’t want to have to adjust each preamp’s volume control every time you need to adjust the volume.

Because this was a planned feature for the UP2 and UPP we needed to make sure it worked perfectly before we started shipping the preamps so whilst we still have all of the preamps in our lab undergoing testing before we ship them what better time to test out this feature which is why we have spent the last week updating the firmware and hardware to make sure it all works as advertised. As an example we took 6 preamps and chained them all together in a one-master five-slave system to give a total channel count of 48 channels !. We also loaded the simple Audioweaver pass through example which feeds a stereo signal directly to all 8 channels but this could be any design of your choosing. It also helps us test the HDMI I2S input and the Link-Port HDMI output ports on the preamp at the same time 😉

The bottom preamp is assigned the master preamp and the top five preamps are assigned slave preamps connected in daisy chain fashion using HDMI cables.

These preamps operate in perfect sync with each other and the master preamp controls the volume, balance and muting on all of the other slave preamps in perfect unison.



48 channel VU meter operating in real time !



Muting works across all preamps as well.



A 48 channel Preamp playing vinyl

Since we have an interest in using some of the products from Purifi Audio in a new project this article makes for interesting reading

https://www.hifishark.com/article/visiting-purifi-audio

The Latest test results and measurements from our Lab show the Ultimate-Preamplifer 2/+ meets or exceeds its design objectives by a huge margin ! Click here to view more.

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

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

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

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

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

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

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

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