miniDSP SHD Power & Hypex NC400 Class D Amps

[babadono]

Langston are you familiar with the InGenius balanced input IC from THAT Corp?

[Langston]

3 hours ago, babadono said:

Langston are you familiar with the InGenius balanced input IC from THAT Corp?

 

I am very familiar with THAT Corp, you obviously are too, but the following may be of interest to others. : )

 

Here's a reformatted summary of the why's and how's of the design.

 

The designer, Bill Whitlock, is tenacious, brilliant and one of the most giving people I've ever met in pro audio. He's retired now but still teaches on grounding and other topics at a level that no one else can or will compete with. He too wears "No BS" buttons, though with a bit more illustration. : )

 

He's a transformer man (ex-Jensen president) and designed and patented the circuit you're referring to that achieves about a fifth of the common mode impedance (10MΩ) of a top of the line Jensen transformer (50MΩ). That allowed it to achieve better than 90dB CMRR for source imbalances up to 1kΩ. That means an unbalanced RCA output feeding this thing will have 90dB+ full bandwidth common mode rejection! That's why the best pro audio mixing consoles offered transformer I/O back during analog's hey-day.

 

The one Achilles heel that all active input circuits have is the limitation (think clipping) of not being able to deal with common or differential mode voltages exceeding their power supply rail (24V max). Much above that you have to pre-clip the incoming voltage with diodes to protect the chips. Jensen's best input transformer, the JT-16-A, can handle 250V for a minute and peaks many times that.

 

Some of the best sounding audio gear ever made uses transformers - their problem is cost, size and weight relative to chips. This was the source of my interest in getting to the bottom of the autotransformers a couple of months ago after I saw one in my Klipschorns. It also accounts for my pro-autotransformer bias, which they proved to deserve. I'm very biased about many things. : )

 

I've read everything Bruno Putzeys has written that I can find and that guy knows his stuff and obviously has pro audio background. He's the first consumer amp guy I've seen that is serious about the "Pin-1 Problem" and the fact that he added an instrumentation amp frontend to the Hypex modules means he's fully knowledgable about common mode issues. He also mentioned that the Whitlock patent made the bootstrapped instrumentation amp too expensive for him, thus the NC400's common mode input impedance is "only" 1MΩ or so. Still world-class compared to every other amp input out there other than the AHB2, which also uses the non-Whitlock instrumentation input.

 

- - -

 

So back to the cheap and cheerful Little Bear passive attenuator. Its use of ganged potentiometers makes impedance unbalancing unavoidable, but nothing along the lines of the 1kΩ imbalance that Whitlock's design or transformers or the AHB2 or the NC400 would care about. But it will trip up the CMRR of standard balanced inputs ubiquitously used elsewhere, such as in the new Purifi modules. This STILL isn't a problem unless you have common mode voltages on pins 2-3 due to EMI near a much longer run of cables than a home setup will normally have. Even then you can simply move the cable a foot or two from the EMI source and all is well. A matched switched resistor attenuator will maintain tight balance, but again that's unnecessary if you have 1MΩ+ common mode input circuitry.

God bless you and your precious family - Langston

[ClaudeJ1]

14 hours ago, Langston said:

Back to the issue of padding the inputs of amps that have too much gain - the $37 passive attenuator that Claude provided a link to really is amazing for the money.

I don't have the Instrumentation or experiences you have in Measuring Audio.

 

However,  I know what actually works in the real world after setting up so many iterations of my various horn "stacks" and HT/2ch. configurations in 8 different domiciles in the last 14 years. I'm still working on one for the basement 2.2 setup.

 

Nice to see you find my simple and inexpensive solution (I use XLR to XLR short cables with my NC-400) that works Backwards from the Large, High Gain HORNS that have 10-20 db more SENSITIVITY than the average, small 88 db/W direct radiators that the Home HiFi Crowd seems to prefer, with their higher Intermodulation distortions!

 

Inserting a variable passive component where it does the most good in a benign manner has an approach that has worked for me. I was just sharing the good without trying to measure the bad, if any. It certainly made an audible improvement by giving Room Correction the Operational Window it was looking for to work within the voltage/gain range that produced optimum RESULTS in each of my rooms!

[babadono]

8 hours ago, Langston said:

He also mentioned that the Whitlock patent made the bootstrapped instrumentation amp too expensive for him,

Hmmm... they're like $6.35 per and less than $3.50 in 1000 quantities. That's too expensive? When you can pass the cost to your customers?

[babadono]

BTW re the AHB2. You have two of those beasts?

[babadono]

@Langston, don't know if you ever saw my posts when I was building a Class D amp but i like using these little boards from SparkFun

https://www.sparkfun.com/products/14002

https://www.sparkfun.com/products/14003

I replace the 1206 with 1200 on the 14002 board because I don't want to give up the 6dB. I used the InGenius input to provide diff. input then ran the single ended signal to a "gain" pot, then ran the attenuated signal to the OutSmarts board to provide a true diff. signal to the  TI Class D amp. That's how I solved the 'no gain control" issue.

[Langston]

3 hours ago, ClaudeJ1 said:

However,  I know what actually works in the real world...

 

And that is what matters.

 

Measurement is my single greatest instructor that began in earnest to prevent and predict failures in my concert work and I never had a show go down or an installation fail largely because of it. I also found hundreds of low-lying cherries to pick to make things better, mainly with loudspeakers, due to measurement. The most important thing I continue to learn are measurement's shortcomings. It's a much longer list than its strengths.

 

Still, measurement is great fun and and I personally would not enjoy tinkering with my audio system without it. It weeds out most of the obvious and not-so-obvious stuff, but still leaves a large gap that can only be closed by listening. Many of the folks in the "measurement is god" camp will never experience a really good playback system because their religion prevents it. Same for many on the opposite end of the spectrum, but at least they may stumble onto it if they have any money left after buying cables.

 

Perhaps more than any other discipline, audio engineering involves not only purely objective characterization but also subjective interpretations. It is the listening experience, that personal and most private sensation, which is the intended result of our labors in audio engineering. No technical measurement, however glorified with mathematics, can escape that fact. - Richard C. Heyser

 

The "measurement is god" website I learn much from brings this to mind:

 

God bless you and your precious family - Langston

[ClaudeJ1]

1 minute ago, Langston said:

The most important thing I continue to learn are measurement's shortcomings. It's a much longer list than its strengths.

What do you think of the ABX box? I was there when they unveiled it at a local Michigan Chapter of the Audio Engineering Society. David L Clark did the demo over 44 years ago.

[Langston]

15 minutes ago, ClaudeJ1 said:

What do you think of the ABX box?

 

Subjective measurement?! You surely don't think that interests me??

 

I have one. Works great. We should do a meeting somewhere and embarrass ourselves with it! : )

 

 

 

God bless you and your precious family - Langston

[ClaudeJ1]

1 hour ago, Langston said:

Subjective measurement?! You surely don't think that interests me??

 

I have one. Works great. We should do a meeting somewhere and embarrass ourselves with it! : )

Since you have one. Why didn't you use it to compare the AHB2 to the NC-400? 

[babadono]

1 hour ago, Langston said:

We should do a meeting somewhere and embarrass ourselves with it! : )

https://getyarn.io/yarn-clip/d8ad202e-86e0-42b9-8d1d-347de3f6e8de

[babadono]

I will not be able to hear a difference between the AHB2 and the NC400

Now between a Jubilee and a Heresy yes I think so.

Is that QSC unit a full implementation of the Dave Clark ABX Comparator?

I had no idea that any company made those.

 

[ClaudeJ1]

21 minutes ago, babadono said:

I will not be able to hear a difference between the AHB2 and the NC400

Now between a Jubilee and a Heresy yes I think so.

Is that QSC unit a full implementation of the Dave Clark ABX Comparator?

I had no idea that any company made those.

 

The originals were maybe 300 in number. QSC made one, but you can get a better one for $999.00 from VanAlstine.

[Wirrunna]

Has anyone run this on Langston's recordings - https://www.libinst.com/Audio DiffMaker.htm

[Langston]

1 hour ago, Wirrunna said:

Has anyone run this on Langston's recordings - https://www.libinst.com/Audio DiffMaker.htm

 

DeltaWave does what DiffMaker does and a whole lot more. It showed the AHB2 modifying the audio much less than the NC400, but it showed most of that difference below 500Hz and above 20kHz (we're dealing with 96k/24bit files). Where I heard differences was in the midrange where this software said both amps were nearly the same. DeltaWave does all kinds of cool things like matching time, frequency and level, then plotting the results of over a dozen comparisons between the files and then allowing you to listen to the difference as well as the reference and file under test. It even has an ABX facility, but I much prefer hardware solutions for that kind of thing to eliminate the computer from the loop.

 

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. : )

 

I did listen to the files I made available to download as if I were one of you and the difference is there to hear. Not quite as clear as the original playback, but good enough if you have a very good playback system.

 

God bless you and your precious family - Langston

[mikebse2a3]

15 hours ago, Langston said:

The designer, Bill Whitlock, is tenacious, brilliant and one of the most giving people I've ever met in pro audio. He's retired now but still teaches on grounding and other topics at a level that no one else can or will compete with. He too wears "No BS" buttons, though with a bit more illustration. : )

 

He's a transformer man (ex-Jensen president) and designed and patented the circuit you're referring to that achieves about a fifth of the common mode impedance (10MΩ) of a top of the line Jensen transformer (50MΩ). That allowed it to achieve better than 90dB CMRR for source imbalances up to 1kΩ. That means an unbalanced RCA output feeding this thing will have 90dB+ full bandwidth common mode rejection! That's why the best pro audio mixing consoles offered transformer I/O back during analog's hey-day.

I have been researching Hum, Buzz and Ground Loop issues and CMR for over a year now and have been the most impressed with Bill Whitlock research and works..!!!

I have implemented Jensen Isolation Transformers in many key locations of my system not because I had any obvious audible issues but more so to guarantee the maintaining of the highest signal integrity. The logic, measurements and listening test have convinced me of the superior method of coupling equipment using high quality transformers (preferably input isolation transformers as the best option over output isolation transformers) like Jensen designed units.

 

miketn

 

 

 

 

[Langston]

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 12.37dB gain and clip at 8V (9.3V at 8Ω)* instead of 2V. Got the padding I wanted and cut the noise in half as a bonus.

 

* Line level consumer audio devices typically clip from 2V to 5V, line level pro audio gear typically clips at a minimum of 12V. There's a reason this amp came with 26dB of gain.

 

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

[Chris A]

9 hours ago, Langston said:

I thought a little salt for the wound would be medicinal. : )

😊  Perhaps the dust has settled just enough to comment now.

 

Note that my experience was with the Hypex FusionAmps (which were designed after the NC400)...was a fairly terrible experience...one that I couldn't believe was occurring when I first heard them after dialing everything in carefully. 

 

This leads me to believe that the designers of the Hypex FusionAmps either didn't catch the problems using their ears (and/or loudspeakers and listening rooms), or they just didn't care.  Neither case is very attractive to talk about, and it has shaken my trust in this company's products (i.e., all of their products). 

 

_______________________________________________________________________________

 

16 hours ago, Langston said:

...Measurement is my single greatest instructor that began in earnest to prevent and predict failures in my concert work and I never had a show go down or an installation fail largely because of it. I also found hundreds of low-lying cherries to pick to make things better, mainly with loudspeakers, due to measurement. The most important thing I continue to learn are measurement's shortcomings. It's a much longer list than its strengths.

 

Still, measurement is great fun and and I personally would not enjoy tinkering with my audio system without it. It weeds out most of the obvious and not-so-obvious stuff, but still leaves a large gap that can only be closed by listening. Many of the folks in the "measurement is god" camp will never experience a really good playback system because their religion prevents it. Same for many on the opposite end of the spectrum, but at least they may stumble onto it if they have any money left after buying cables.

 

Perhaps more than any other discipline, audio engineering involves not only purely objective characterization but also subjective interpretations. It is the listening experience, that personal and most private sensation, which is the intended result of our labors in audio engineering. No technical measurement, however glorified with mathematics, can escape that fact. - Richard C. Heyser

I think that this is a very good point of view, and one that should elicit a little self-reflection on this pastime/hobby (i.e., not a profession to make money for living).  I also think that a lot of folks like to obfuscate this point because they haven't taken the time/effort to learn how to do acoustic and electrical/electronic measurements--and interpretation of the results.  The onus is still on them, I think to negate this balanced viewpoint enunciated just above.  It includes both listening and measurements-together.

 

14 hours ago, babadono said:

I will not be able to hear a difference between the AHB2 and the NC400

Perhaps...or perhaps you might...  I'd re-read what Langston said:

  

On 8/9/2021 at 8:05 PM, Langston said:

After a while of listening, "dryness" became my primary impression, everything was there but it wasn't pulling me into the music like usual. Maybe I'm just tired or something I thought, so it was time to switch the AHB2 back to the horns.

 

The moment I started playing music again it was over. The AHB2 brought back the liquid, not more detail, but the smooth spread of the recording environment was filling the space between the loudspeakers again with increased depth and pulling me into the music.

 

The difference was pretty significant, though I could easily see myself enjoying the NC400's if I hadn't heard the AHB2. The NC400 reminds me in a way of my MC275 tube amps, just the opposite end of the spectrum. The MC275 is too liquid and too soft, the detail is there but too laid back for my taste. Whatever that means. : )

 

It's been my experience that the subjective aspects of listening can sometimes reveal great truths about our pastime (listening to great music being reproduced), if we allow ourselves the opportunity.

 

I found a great truth a couple of years ago that was astounding to actually hear, and one that basically no one apparently talks about.  I attribute this situation to the problems that most people experience in terms of the capabilities of their setup:

 

1) not having full-range loudspeaker directivity,

2) not having full-range horn loading (to achieve extremely low modulation distortion), and

3) not controlling nearfield (early) reflections. 

 

Once you control for these three deficiencies (all simultaneously), then phase response, the other half of the transfer function, becomes an audible variable that differentiates "so-so" subjective sound quality from "outstanding", and suddenly becomes a key performance criterion.  Apparently, few people have taken the required steps to hear this effect (especially researchers who write technical articles).  Such is the one-sided nature of a world that is overwhelmingly populated with direct-radiating loudspeakers that have no real directivity control below 1-2 kHz, lots of limitations on the dynamic range of their loudspeakers before modulation distortion dishes out so much "mud" that they can't hear the music details (including the same issues in the recording that they select to do their subjective listening studies--as Greenfield and Hawksford apparently found), and in-room early reflections that destroy the subjective effects of flat phase response loudspeakers in-room.

 

Apparently, this same type of experience exists in amplifier performance, but perhaps not as well understood as in loudspeakers, and the measures used to date that apparently don't identify the objective measurable differences between amplifiers that lead to the differences in these sort of subjective listening experiences.

 

Your mileage may vary (...but not by very much, in my experience).

 

Chris

[Langston]

On 8/11/2021 at 4:06 PM, ClaudeJ1 said:

Since you have one. Why didn't you use it to compare the AHB2 to the NC-400?

 

If you've done a double blind thing before you know why I didn't - it's just a tad less painful than waterboarding. Maybe. I much prefer saturating myself with a few tracks over the course of a half hour or so, then switching amps. The change is immediately apparent usually.

 

I looked into the apparently unavailable VanAlstine ABX unit and it doesn't appear nearly as well executed as the QSC. Whatever the case, I cleaned and calibrated my unit today and it measures like it's supposed to - like a wire. Switching with the IR remote is silent and the audio path is DC coupled and completely passive. It accepts balanced and unbalanced line level devices and ground referenced or bridged amps. It has an internal 1kHz 1V generator that is used to make both channels of both amps the same volume. The 3 digit numerical display shows the voltage reading after it passes through the amp channel. I used a balanced switched resistor passive attenuator to bring down the NC400's within 0.29dB of the AHB2.

 

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 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.

 

God bless you and your precious family - Langston

 

* Edit on 27 Oct 2021: I just figured out the probability math on this and you divide the possible "combinations" of getting 8 right (r) out of 11 trials (n) "without repetition" by the compound probability of two possible outcomes (right or wrong choice) over 11 trials. This latter number is the denominator and in this case is simply 2^11 = 2,048. The numerator requires a tiny bit of statistics math that can be done here and works out to be 165. Then the probability or level of confidence that I in fact heard a difference between the two amps when selecting 8 right out of 11 ABX trials = 1 - 165/2048 = 92%. Pretty good, but the rule of thumb the stats folks use is 95% or better to be sure enough to start bragging. : )

 

ABX testing requires a bunch of wiring

 

Classic excellence

[gnarly]

Langston, may i ask a quick question unrelated to thread topic.........what does the Q-SYS Core do?

Thx,  Mark