miniDSP SHD Power & Hypex NC400 Class D Amps

[babadono]

On 8/11/2021 at 8:00 PM, Langston said:

Hey Claude!

 

I thought a little salt for the wound would be medicinal. : ) I got another 6dB of S/N out of the NC400 to equal the AHB2 and Purifi amps by removing (Rg) from the instrumentation amp section. This means the NC400 now shares best in class noise specs with the AHB2 while having superior CMRR compared to the Purifi amp. The NC400's now have 13.37dB gain and clip at 8V instead of 2V. Got the padding I wanted and lost some noise as a bonus.

 

The schematic as a review

 

The location of (Rg) labeled R141 on the amp module

 

NC400 modified S/N

 

NC400 modified noise

 

God bless you and your precious family - Langston

So you changed it from a true IA to a Diff. amp with buffered (voltage follower) Inputs. How does this add 6 db to the S/N ratio? I am very curious about this, I have a lot to learn. The input buffers do have a bias resistor on their non inverting inputs correct? They are just not shown in the block diagram for simplicity? What is their value?

[babadono]

10 hours ago, Langston said:

You're supposed to go through 25 ABX trials before giving up, but I only made it to 11 tonight. Sometimes I finished a trial within seconds, sometimes it took several grueling minutes. I got 8 (73%) right and I'm sure I can get in the 90's tomorrow when I'm not tired. For me, a solo female soprano is usually the best amp separator.

As I alluded to in an earlier post I am a feared I could/would do no better that 50/50 in an ABX test of the AHB2 and the NC400. You my friend I think have very good/trained hearing. As does @Chris A. Cie la vie.

[babadono]

What is the unit in the top of this rack with all the phoenix connectors?

[Langston]

On 8/13/2021 at 1:45 PM, babadono said:

What is the unit in the top of this rack with all the phoenix connectors?

 

It's a Q-SYS processor. : )

 

On 8/13/2021 at 7:03 AM, gnarly said:

.what does the Q-SYS Core do?

 

As you know - anything you can imagine pretty much. : )

 

I got the Linux based 48k/24bit 250i Core (the top 2 space unit in the pictures) in 2012 (!) as a digital playground for my ideas in concert production. I had been using a Peavey Media Matrix processor prior to that for that purpose, but QSC bought almost all the Media Matrix engineers. If you've ever worked with the Media Matrix line that preceded Q-SYS, the programming and software component interfaces are obviously authored by the same people. QSC pretty much unleashed those engineers for a while and they achieved what is still sine qua non of the realm. Now Q-SYS development is focused on video and remote meeting integration which reminds me a bit of my beloved Mac computers morphing into cheesy web surfing iPhone extensions. I hope QSC can resist the Borg..

 

Oddly, my old 250i is still current - the I/O cards haven't changed and the software/firmware updates are still fully supported. QSC's tech support and service on these things is also without equal. I still have free 24/7 support if needed, which it isn't. That's for installers that learn just enough about a product to sell it, then find out the customer really needs it to work correctly for an event the next morning. On the ABX, which ceased production in 2004, I left a voicemail with QSC last night asking for a schematic (don't need it, just want it), and a tech guy I've dealt with for over a decade there replied this morning offering his help to solve any problems I had, but said he couldn't give me the schematic unless I was an authorized QSC service center. About a minute ago I got another reply from him with details on the audio path I was interested in.

 

/end QSC fanboy brag/

 

In my home setup, I use the Q-SYS in the digital domain only, it's analog A/D/A is very good, but I chose to output digital from my Mac mini Roon music server via the miniDSP UDIO-8 into the Q-SYS, then from the Q-SYS to Benchmark DAC3 converters.

 

I separate processing logic into pages to keep things simple and pretty. Doesn't cost any processing cycles.

 

 

Clicking on the Klipschorn DE750 page reveals its processing modules. I opened (2) of them to show you something you may not be aware of. Not only can you upload inverse FIR filters to convolve with the audio stream, but you can skip the zero latency minimum phase (Proportional Q) 32 filter parametric module and use the custom IIR module that takes up to 32 biquad sets. Biquads allow you to do anything you want with an IIR filter, vs. the constraint imposed by the standard parametric filters (not that it's much of a constraint, they are actually forcing you not to do stupid stuff by limiting things). Of course you can daisy chain components to increase filter counts, but that would mean you don't know what you're doing. Fewer is better. Do it Chris's way, make everything as perfect as possible physically first, acoustically second, then use this stuff as icing on the cake. If you want the best result, that's the way to pursue it.

 

Here the transfer function of the FIR (for the full loudspeaker system) and IIR filters (for the HF system) are shown:

 

 

The same thing, just impulse response view. Notice I only needed about 6ms delay with the FIR to correct the system-wide time domain:

 

 

God bless you and your precious family - Langston

[babadono]

Ok there's smoke comin' out  my ears now cuz ur blowin' my mind

[gnarly]

Thx, I saw the AES3 cards and was hoping you were using it for your digital signal processing.

But like you say, anything can be done with the Cores, and maybe you had something else going on with it...

 

I'm such a huge Q-SYS fanboy too...

Here's the schematic I'm currently listening to.  It's for a 4-way MEH on top a dual 18" sub.

500i fed via Q-Lan from a 110f. 16384 taps on all FIR filters!  (just to keep from messing with different delays Lol)  Now i just need the super amps you guys are talking about 😁

[Langston]

On 8/11/2021 at 6:12 PM, Langston said:

DeltaWave does what DiffMaker does and a whole lot more...

 

...Obviously this kind of software is yet another attempt to quantify perception, yet requires subjective interpretation to do that. It's not useless, and it is best of breed, but another miss just like DiffMaker. IMO...

 

After several days playing with DeltaWave, my opinion has changed. It's an excellent effort to do what may be impossible (quantifying perception), but just like other forms of measurement, it can help in this regard if you figure it out. I can't imagine how many hundreds of hours the author put into it only to release it for free. Audio has some amazing people in it. : )

 

The following plots are called Delta Spectrograms, which are 3 dimension difference plots of the frequency domain (amplitude, frequency, time) of the reference recording (direct output of the DAC3 converter) vs. the comparison recording (output of the AHB2 or NC400). If I were to use the same file for the reference and comparison, the plots would be solid green (no difference).

 

This is just for fun, but it continues to imply that there is more difference between the NC400 and the original than the AHB2 and the original.

 

AHB2 vs. Original

 

NC400 vs. Original

 

God bless you and your precious family - Langston

[Langston]

One more thing I thought would be interesting is to use the scope to measure the ultrasonic output of the NC400 at the end of a 25ft Canare 4S11 cable (14AWG quad) while connected to a biamped Khorn. There are no passive components, just the Crites cast-frame woofer and the DE750 compression driver.

 

I made (3) measurements, none of which had signal applied to the amp. The first was with a 4Ω resistor across the output without the loudspeaker cable, the second had the scope probes on the woofer input terminal block, the third had the probes on the input terminals of the DE750.

 

The take-away is that there's little difference between these measurements, thus the ultrasonic noise from the amp is very low impedance and the loudspeaker cable capacitance and driver loads did nothing to attenuate the noise. Nevertheless, both passbands are in the hundreds of ohms at these ultrasonic frequencies, thus almost no ultrasonic current is passing through the voice coils. (Approx. 0.4V at 400kHz fundamental switching frequency; current = volts/Ω).

 

4Ω Load

 

Khorn Woofer

 

DE750

 

God bless you and your precious family - Langston

[Edgar]

7 hours ago, Langston said:

Nevertheless, both passbands are in the hundreds of ohms at these ultrasonic frequencies, thus almost no ultrasonic current is passing through the voice coils. (Approx. 0.4V at 400kHz fundamental switching frequency; current = volts/Ω).

 

Crites specs the CW1526C at 1.0 mH inductance. That alone results in an impedance of 2.5K Ohm at 400 kHz, so there it almost no current flowing into the voice coil.

[Chris A]

Well...the saving grace is that, unless there are strong nonlinearities in the system somewhere, subharmonics are very difficult to generate, much less hear, and the bandpass nature of acoustic drivers act as a strong "crossover" to reject those frequencies.  The tests of human hearing above 20 kHz in the 1980s were apparently corrupted by aliasing, which is very audible, so for years, some people thought humans can hear above 20-21 kHz. Alas, such is not the case, and the frequency analyzer in the human ear (the cochlea and its associated structures) strongly rejects frequencies above 20-21 kHz--by apparent design. 

 

But as you are probably about to say, one never knows the effects of that added ultrasonic noise--that is impossible to completely filter out in the amplification loop during playback.

_____________________________________________________________________________

 

In the case of SACDs (i.e., DSD music files), they also have huge amounts of ultrasonic noise or aliasing effects that must be filtered out during recording and playback.  To my ears, the anti-aliasing filters used during recording do a good job of filtering out recorded frequencies above 20 kHz to prevent aliasing problems. SACDs, as provided by the record companies, seem to have the least amount of editing of the original downmix tracks, which of course preserves the their SPL and phase (transfer function) fidelity, and is probably what I hear as "higher quality" and "much more engaging" subjective listening effects.  They are, in fact, extremely enjoyable to listen to in my experience, especially multichannel (5.1) recordings of higher overall recording and production quality than the norm for PCM 44.1 CD files.

 

As most good engineers know, there are always tradeoffs in design--always.  I've had a bad experience with class D amplification with DSP-front-end, but extremely good luck with many DSD recordings. Apparently the design tradeoffs selected in the prior case were not as successful as in the succeeding (completely different) case.

 

Chris

[ClaudeJ1]

25 minutes ago, Chris A said:

I've had a bad experience with class D amplification with DSP-front-end, but extremely good luck with many DSD recordings.

Like those who say "Analog is better than Digital, without specifics. The world is full of irrelevant contradictions, aye?

[Edgar]

50 minutes ago, Chris A said:

In the case of SACDs (i.e., DSD music files), they also have huge amounts of ultrasonic noise or aliasing effects that must be filtered out during recording and playback.  To my ears, the anti-aliasing filters used during recording do a good job of filtering out recorded frequencies above 20 kHz to prevent aliasing problems.

Unfortunately, SACD/DSD/1-Bit Sigma-Delta is fundamentally flawed: https://timbreluces.com/assets/sacd.pdf

[Chris A]

1 hour ago, ClaudeJ1 said:

Like those who say "Analog is better than Digital, without specifics. The world is full of irrelevant contradictions, aye?

 

I'm an engineer by upbringing, education and career.  My experience has been that it's the choices made during design that predominantly determine the success of the produced products in the marketplace. 

 

By way of a now-famous example of this point: in the 1960s-1980s, the "big three" Detroit automakers generally engineered autos with not-so-good quality/reliability standards (by comparative standards to their across-the-Pacific competitors), and the result of what was to become a defining management cultural clash which became "The Machine that Changed the World". 

 

It wasn't the assembly workers, but the engineers that designed the finished products (the autos) and the system that produced the product (the manufacturing and supply systems).  Ford largely led the way in the US to their own recovery after they were basically being handed their heads by Toyota's and Honda's then-comparatively superior auto design and manufacturing systems in the 1970s-1980s.

 

So yes, largely, it's in the hands of those doing the design (and that especially includes upper management of the organizations that control what the engineers do).  We since have gone through "lean", "six sigma", and other "revolutionary" practices (which really disguised how bad their system designs really were beforehand, in terms of what the buying customers got--but not the profits reaped by those holding stock options). 

 

That also applied to electronics--and Motorola led the way to their own recovery vs. their competitors in the 1980s.  See "The Parable of the Boiled Frog" for the story of those companies that didn't make that transition.

 

So in a long-winded fashion (...I must be suffering from K-forum withdrawal, or at least subjectively realizing the importance of this forum what its loss might mean...), I think I answered your rhetorical question, above. 

 

Apparently Class D is much more difficult to do well than it appears, and probably still has a distance to go before it really does overcome class A and AB design performance, and the hunt for, I believe, is still on for the source of the sonic differences between the two approaches.  This viewpoint was one I adopted from reading Nelson Pass' views on this subject.  I trust that guy in this particular domain.  I believe he said that class D will probably ultimately triumph--but just not that he's actually seen/heard yet.

 

Chris

[ClaudeJ1]

26 minutes ago, Chris A said:

Apparently Class D is much more difficult to do well than it appears, and probably still has a distance to go before it really does overcome class A and AB design performance, and the hunt for, I believe, is still on for the source of the sonic differences between the two approaches.  This viewpoint was one I adopted from reading Nelson Pass' views on this subject.  I trust that guy in this particular domain.  He I believe said that class D will probably ultimately triumph--but just not that he's actually seen/heard yet.

 

Chris

I worked a summer job driving cars off the Chrysler assembly line and experienced the "quality variable" first hand in the 70's after High school.

Working in Automotive Electronics Engineering in the 80's, I agree 100% of your points about Japanese Quality standards and methods created by W. Edwards Deming initially.  (I've also owned all of the brands of cars, including Toyota (GM's quality benchmark), and currently, Honda.

My project got the very first QSP Award from General Motors in the late 80's when they finally giving the Q more than lip service, but let's not forget about the PRICE portion.

 We also did some E Modules for Honda, and I discovered first hand how Picky they can be about Non Compromising on Quality. Ford was our biggest customer and they were into Taguchi Methods. The Dean of UofM Engineering school had dinner at my house, when I lived next door to a Ford VP. He said they took apart the Honda Accord at Ford Motor Engineering and were surprised to find that it went back together without using any Force. The Japanese simply knew how to hit the peak of the variance curve consistently and make higher quality parts, across the board, while maintaining a lower price.

Same is true with Audio Components. Using 1/2 percent, Low Noise, metal film resistors and poly capacitors yields a better product, all other things being equal in Design, which they seldom are. Surface Mount Technology (of which, I was a Pioneer) shortens the distance between 2 points and reduces the dreaded Parasitics in PCB design.

But State of the Art does advance for all products regardless. I agree that Management drives the Bus that Engineers are forced to ride in.

I still have 2 class A amplifiers which I intend to use with my modified (by me) Edgar Titan II's. I've always been a fan of the better Phase behavior of LaScalas vs. Khorns (PWK, AFAIK, didn't think phase was important). I also felt that Straight Axis Horns would be better than folded ones, where a practical size limit would demand a Subwoofer below 80 Hz.

Either way, I'm glad you and Langston belong to both the Measure AND Listen camps, which supports my own viewpoints about Audio, and Horns, more specifically.

Either way ALL amplifiers today are better than they were in the 70's and 80's with very few exceptions!

 

 

[Langston]

Claude! I thought maybe I'd lost you forever! OT, but you are probably the most encouraging person on this forum. As I catch up on things around here I've noticed that you make a habit of complementing everyone throughout your years of involvement and I feel bad about this semi-Class D smackdown. OTOH, it's hilarious that there's another much larger thread about "Class D amps are cool" right next to this one! What a wonderful world! : )

 

You will have to put up with me in your home when I visit my son in Chicago again. I want to hear that system. And of course make fun of the amps (after I steal the K-402's). : )

 

The paper that @Edgar referenced is amazing and relevant. I was too busy with concert production to pay much attention to SACD when it appeared, but kept hearing that there was more to the story than the marketers were publishing. Lipshitz and Vanderkooy have always been entertaining - my favorites were their arguments vs. Heyser about group delay and arrival time of drivers in multiway systems. The exclamation marks are the best. What's also fascinating at the end of the paper is the tight correlation between their SACD criticisms and those I'm learning about Class D.

 

A final point that Chris made about production quality vs. format shouldn't be missed. Formats intended for the audiophile community such as SACD and higher than CD multi-bit recordings almost always bring more effort to the recording and mastering of the final product. I noticed this the first time on my laptop just clicking on the song clips available on HDTracks while switching resolutions. The higher resolutions on the same album often sounded much better on my dumb laptop speakers - that cannot have anything to do with bit rate and digital resolution - they're either dumbing down the 44.1k previews or the high res. stuff is mastered differently.

 

God bless you and your precious family - Langston

[Chris A]

12 minutes ago, Langston said:

The higher resolutions on the same album often sounded much better on my dumb laptop speakers - that cannot have anything to do with bit rate and digital resolution - they're either dumbing down the 44.1k previews or the high res. stuff is mastered differently.

Yes...

[ClaudeJ1]

On 8/21/2021 at 12:38 PM, Langston said:

Claude! I thought maybe I'd lost you forever! OT, but you are probably the most encouraging person on this forum. As I catch up on things around here I've noticed that you make a habit of complementing everyone throughout your years of involvement and I feel bad about this semi-Class D smackdown. OTOH, it's hilarious that there's another much larger thread about "Class D amps are cool" right next to this one! What a wonderful world! : )

 

You will have to put up with me in your home when I visit my son in Chicago again. I want to hear that system. And of course make fun of the amps (after I steal the K-402's). : )

The K-402's are heavily guarded by a Dobie-O-Matic mechnical attack dog, so you will have to be quick. "You can't steal in slow motion" is a truism. You are welcome any time. I consider you and ChrisA as some of the sharpest leaves on the Klipsch Tree. Many Klipscheads have been over here to satisfy their curiosity.

 

I did not take your findings as an smackdown to Hypex tech at all. Just the very best A/B, I've ever seen.

 

Also, I'm not of 100% the "Stereo Review/Julian Hisrch" school of thought that "all amps sound the same" if they measure the same (only 50% actually, LOL). I used to be indecisive, but now I'm not so sure. LOL.

 

That being said, one must wonder the eternal question about anything man made in this world: "When is good enough, enough?"

 

I remember when the Sonic Impact Chip T-amps in the early 2000's blowing away reviewers with their sound coming "close" to $20,000 tube amplifiers, which knocked them on their butts for only $25! Since I'm all about "get it while you can" as the best bang for buck attitude, I bought 3 of them. I even sold my Khorns in 2007 with that amp on 8 AA batteries driven by a Sony Walkman CD player and Roy's Demo tunes after a trip to Hope!!!

 

I brought one to Klipsch HQ in Indy and had it tested by an Engineer who concluded it was a "very good 6 watt Amplifier" which I still use for curving drivers and complete speakers using an overkill power supply for it.

 

Different is never the same, but at some point, one has to declare "Close enough."

 

Besides, anyone in this world who thinks ANYTHING man-made is Perfect, needs to increase their Magnification! LOL.

 

I have an autographed copy of the book by my good buddy Richard F. Lyon (inventor of the Optical Mouse and Google Street Camera) former Chief Engineer at Foveon, founded by Carver Mead, creator of all things digital and author of "Moore's Law." I was part of a 3-year "Mentor" program with them 20 years ago in testing the best digital camera in the world at the time, that bore the Hasselblad name in Europe. It's called "Human and Machine Hearing." It's an incredible work that can fill in a few gaps left by the inadequacies of bench measurement equipment, but it's too deep for my tired brain. I'd rather just listen to music on my horns.

[NBPK402]

Basically, the NC-400 is the Easiest Kit you will ever build, guaranteed. Then when you compare the sound of it's First Watt to a Real First Watt Amplifier (Pass Class A) on HORNS, you will realize that your have the same Sound Quality as the Class A, without the built in "space heater" of Class A.
 
FYI, I never shut of my NC-400's, only the Pre Pro, CD player and 4K Blue Ray/4K OLED are shut off. Same is true for the subwoofer power amps, and the TI Chip Amps I use for the surround channels, their Quiescent Current wouldn't even charge my iPhone, so they are on too.
 
The Hypex is like Class A sound quality with Seemingly Unlimited Headroom with HORNS, which I only come close to "using up" on my demo drum recording that hits 124 db peaks!!
 
One word of caution that I mentioned before with the Hypex and other amps with no gain controls:
It bears repeating, with Horn Speakers, you need to attenuate the drive Voltage from your preamp with Potentiometers.
 
The Extreme Sensitivity of Horns requires lowering the always Too High Voltage gain of all High Power Amplifiers, and FORCE the Pre Amp or Pre Pro to put out a much higher Voltage Swing for Audio.
 
Remember that all Signal to Noise ratios of Power Amps are measured and REFERENCED TO full output, way above the noise floor. You'll thank me later for this technical tidbit!
 
This is what I use on my NC-400. I have several of these. Worth every penny!!!
 
https://www.ebay.com/itm/253180664213?hash=item3af2be5995:g:6sgAAOSwzExgZTkA

Why not attenuate via your active crossover?

Sent from my SM-G985F using Tapatalk

[ClaudeJ1]

2 minutes ago, NBPK402 said:

Why not attenuate via your active crossover?

Not using one.

[ClaudeJ1]

3 minutes ago, NBPK402 said:

Why not attenuate via your active crossover?

Sent from my SM-G985F using Tapatalk
 

Not using one. All passive for all channels, except Sub. Yamaha 5200 and 5000, soon to be replaced by Nad DAC/PreAmp.