miniDSP SHD Power & Hypex NC400 Class D Amps

[Langston]

Finished the build and Claude was absolutely right - it was so easy that I put together both amps in 3 hours in slow motion (my top speed).

 

Parts, fit, design, everything is class A (pun!). Pictures now, bench tomorrow, weeping or joy Saturday. : )

 

 

 

 

 

 

 

 

God bless you and your precious family - Langston

[ClaudeJ1]

On 8/5/2021 at 9:45 AM, Delicious2 said:

After all these years I guess I still don’t understand how this works. I don’t see how attenuating the preamp processor output into the high powered amps gets the amps any higher above the noise floor.  It certainly doesn’t drive them closer to full output where their specs measure best.  For that we would have to attenuate the amp output between the amp and speaker.

It's mostly about 2 things. Greater physical knob rotational control on the Pre Amp, and in my case, getting the YPAO Microphone Feedback to the unit into it's best operational range.

 

A 2 channel pre amp is easy to explain: How many times have you heard people complain that with Khorns, they can only rotate their Volume Knob from 7 o'clock to 8 o'clock before they get blasted out of the room? Reducing the input voltage at the Power Amp input solves this to give you "normal" 12 O'clock knob indicator setting at normal listening and giving you Mechanical Rotational LATITUDE in the process, OK?

 

In the case of my Yamaha, which has balanced and unbalanced outputs, the BALANCED ones are capable of 8 volts output according to the specs. As you know Balanced cabling, while expensive allows for lower noise and longer runs, but that's not the main reason.

 

When the Yamaha "listens" to the room, it puts out some standard fast frequency sweeps at some pre-determined level. If the sound the Mike sees going back is too loud, it affects the gains at the Outputs going to the power amps and puts the Room Correction algorithms out of their "comfort zone" and calibration points.

 

Since most "standard" direct radiator speakers, on average have an 88 db sensitivity on a good day, THAT is what the Pre Pro looks for to adjust the Relative Levels. They are attempting to get an 83 db level (Reference Levels) when you have your digital volume display at Zero.zero db on the face of the unit. So in order to give the Pre Pro's feedback system the Lack of Sensitivity Speakers it's looking for, we need to knock down the power amp input signal by 14-20 db or so when we use HORNS to make the Room EQ and Level Setting happy in the Pre Pro.

 

Keep in mind that we "Horn Guys" are a 1% Minority in the electronics marketplace. IOW, they don't build electronics for Klipscheads!!

[babadono]

So do you have any idea how they do the balanced gain control? Is it just a four gang pot? I did not see any pics with the cover removed.

[ClaudeJ1]

On 7/11/2021 at 6:00 AM, Chris A said:

I don't personally recommend class D if fidelity is one of your measures of merit.  I'd stick with class A or good class AB instead, and let the class D gravy train go its own way.  My experience with class D has been uniformly poor--even the "high brow class D" amplifiers that have come into vogue. 

 

I read the paper in the link you posted. Pass does not even Mention Class D...................................only negative feedback in linear operation of transistors in Class A and AB.

 

Transistors are much better used as fast Switches, to achieve over 90% efficiency in the process. Bruno Putzeys, who spend 10 years at Philips Electronics Europe developing this technology, has managed to improve it for the 4th time. The measured distortion was so low, they needed to invent more sensitive test equipment the super low distortion.

 

What convince be about it's quality is when I heard the older tech. Hypes amp on the Sadurni Staccato Horns at Axpona in 2014. It was the best sounding speaker at the show and used no more than 1/4 watt of the amp which should not have worked with horns, but it did.

 

Basically I no longer use Spacer Heaters to make music since Hypex makes the best sound for the Buck, of which I'm always conscious about.

 

So instead of spending about 12 grand for 4 First Watt class A Amp channels (and using them to fry my Eggs for breakfast), since only 100 were made and are no longer available (or building my own, which is a real PITA), I went with the best sound I ever heard with what was his Hypex latest generation at the time (over 5  years ago) based on faith and never hearing them. They are a bargain at twice the price, which is still 1/4 the price of good Class A.

[ClaudeJ1]

8 minutes ago, babadono said:

So do you have any idea how they do the balanced gain control? Is it just a four gang pot? I did not see any pics with the cover removed.

Yep. And if you need to convert from XLR to RCA or vice versa, it does that with the push of a switch.

[ClaudeJ1]

14 hours ago, Langston said:

Finished the build and Claude was absolutely right - it was so easy that I put together both amps in 3 hours in slow motion (my top speed).

 

Parts, fit, design, everything is class A (pun!). Pictures now, bench tomorrow, weeping or joy Saturday. : )

 

Well, I guess it's the first time I've ever been "Absolutely Right" about anything, so that is good.

 

What's even better is reading about your measurements and Listening impressions vs. the Benchmark Amp you own that is in the Number One spot (or tied for first place with the new Purifi Amp).

 

I'll be waiting to see if I'm right about that too!

[Chris A]

1 hour ago, ClaudeJ1 said:

Pass does not even Mention Class D...only negative feedback in linear operation of transistors in Class A and AB.

Here is a quote:

 

Quote

You would want to note that the Hypex and most other Class D amplifiers get their performance solely from large amounts of feedback.

I heard what I heard.  It wasn't good.  My wife also heard it and asked what I had done to our sound quality. 

 

Here is the link to the entire post in this thread that you only partially quoted, thus ignoring the core information that I had posted:

 

I don't recommend ignoring what is said in that post, or the quote that I added just above.  The source of that quote is unimpeachable.

 

And my ears agree with him.

 

Chris

[Langston]

Both Hypex NC400 amps measure the same and are so much better than the miniDSP amp that I'm going to drop the comparison after this post and compare the NC400 to the AHB2, which I consider to be the measurement and sonic champ in my limited experience.

 

Another really weird and wonderful thing about the NC400 is that it's self-oscillation noise is benign enough that I can measure the amp directly with my APx515 without the need of an external switching amp filter. Until this point this filter was required for every Class D amp I've measured. The Audio Precision AUX-0040 filter is so well designed that it is nearly transparent to the majority of audio measurements, but it's nice not to have to use it. This in itself sets a new bar for a Class D amp.

 

The output the NC400 is load-insensitive under 20kHz, another first for a Class D amp in my experience. I tinkered around with several APx515 measurements and the results were so good that I decided to turn everything off and plan what I'm gonna do. Plus the day is getting busy 'cause I just turned 62. : )

 

God bless you and your precious family - Langston

 

 

 

[ClaudeJ1]

53 minutes ago, Chris A said:

I don't recommend ignoring what is said in that post, or the quote that I added just above.  The source of that quote is unimpeachable.

 

And my ears agree with him.

 

Chris

I'm not ignoring anything. I read the entire Nelson Pass article and he did not mention Class D even once, just Negative Feedback. Read the white paper by Bruno Putzeys. Feedback in Class D is a whole different animal.

[Langston]

On 8/5/2021 at 8:45 AM, Delicious2 said:

After all these years I guess I still don’t understand how this works. I don’t see how attenuating the preamp processor output into the high powered amps gets the amps any higher above the noise floor.  It certainly doesn’t drive them closer to full output where their specs measure best.  For that we would have to attenuate the amp output between the amp and speaker.

 

Very true, but this is such an important question I'm going to have a go at it, though it's obvious you already understand the essentials.

 

Holding all else constant, increasing the electrical signal to noise (S/N) ratio when driving a highly efficient horn loaded loudspeaker system within a few meters or less of a critical listener is a very big deal.

 

The wider the dynamic range of the music, the more important it becomes. The quietest passages of Copland's Appalachian Spring or Vaughan William's The Lark Ascending lifting from a silhouette of playback system silence is breathtaking and more than worth the effort to achieve. Woe to you vinyl worshippers! : )

 

So.. What to do?

 

You have to have a music source, amplifier and loudspeakers. You can choose how many components (at your pleasure or peril) to add to this, but they are potentially additive noise sources.

 

Since we're talking electrical S/N optimization, we start with the amplifier because we're stuck with it's noise level as the absolute best (quietest) our system can be. The stuff that comes before it can only make it worse AND THAT is what must be avoided and the goal of "gain optimization".

 

Note: when adding noise, two components with equal noise levels will increase total noise by 3dB. Of course volume knobs can increase it more, but let's not make this messy. If you can keep the noise level of one components at least 10dB quieter than the other, there will be no increase in total noise. Want to calculate this for yourself?

 

Analog audio components such as amplifiers have S/N ratios all over the map, but I aim for at least 96dB (16bit CD resolution). I have a Mark Levinson 532H that specs ">85dB" and a Benchmark AHB2 that specs 130dB. The latter sounds better and this may be part of the reason. (The Hypex NC400 measured in the 120's on my bench today)

 

By S/N, I refer to the largest undistorted signal a component can output vs. a noise floor that pretty much stays the same no matter the volume control setting, if any. With a big amplifier feeding high efficiency horn loudspeakers, you will be throwing away S/N and possibly hear noise through the loudspeakers even without music playing. An amp that outputs 10x more power than you will ever use will have you 10dB closer to its noise floor during playback.

 

You have to buy a less expensive amp to achieve better sound! Paul Klipsch was a genius.

 

On the preamp, etc., that feeds your amplifier, you are able to drive it to its full output and you should. This will take full advantage of its S/N ratio, but you'll probably have to turn down the gain on your amp if it has that feature or pad the input like Claude does. This will allow you to keep your amplifier's S/N ratio as the limiting factor in your system.

 

Like everything else in audio, there are diminishing returns where additional optimization (and money) won't audibly help, but we certainly should do the best we can with what we have. Pro amps have always had input gains. Just do it. : )

 

God bless you and your precious family - Langston
 

[Chris A]

6 hours ago, ClaudeJ1 said:

I read the entire Nelson Pass article and he did not mention Class D even once, just Negative Feedback.

That quote was directly from the source you mention. 

 

I'm sure that he doesn't wish to get pulled into this kind of discussion by the person I quoted just above, however.  The person I originally quoted has categorically produced products that have been uniformly praised by those who have tried them on their high fidelity fully horn loaded loudspeakers. 

 

6 hours ago, ClaudeJ1 said:

Read the white paper by Bruno Putzeys. Feedback in Class D is a whole different animal.

To others contemplating Hypex products, clearly Claude hasn't heard what I heard with two FA122s on TAD TD-4002/KPT-KHJ-LF Jubilees, carefully dialed-in (SPL and phase response). 

 

It doesn't matter what somebody else said about feedback in class D amplifiers, and how it's "different".  I cannot recommend any Hypex product or any other class D amplifier based on the same type of technology--based on what we heard here.  It was that bad...at least as bad as any amplifier that I've heard on this setup.  This is why I am speaking up on what I heard based on that personal experience.  The fact that Hypex produced such inferior products (both amplifiers) and put their name on them leads me to believe that all they are doing is linearizing amplifier output via large amounts of feedback so that it measures well with the measures that they have picked.  However, listening to the result of Hypex's approach clearly shows that they are not picking the measures that show the problems that are induced by using those methods. 

 

Chris

[ClaudeJ1]

5 hours ago, Chris A said:

The person I originally quoted has categorically produced products that have been uniformly praised by those who have tried them on their high fidelity fully horn loaded loudspeakers. 

 

I owned 2 of those products (F3 and AlephJ) which sounded fabulous. I also own 2 more Class A amplifiers not designed by him. When I sold my Jube Clones with TAD 4002 drivers (because they did not accomplish my goals in the small space I have) I set them up for the buyer who has SIT-3 and SIT-2 amplifiers, as well as Single Ended Tubes. All sounded excellent. Even the original designer agrees that they all produce PHD, which I use to describe "Pleasant Harmonic Distortion," that is euphoric in nature, just like all the Amps listed here. It's also why he tells all his readers to go build them because he doesn't want to rate the Listening of his own products.

 

I'm pretty sure that you have managed to squeeze the very best performance out of your relatively new, modified Jubilees/K-402s with TAD Drivers as the very best hybrid solution you can hear and measure. I'm also aware that you have helped countless others here and continue to do so.

 

I must also say that when using the very best measuring tools available today, it allows us to see graphs and assign Objectivity and Repeatability to the Quest for best sound. Sadly, the listening part has live humans as the greatest unrepeatable variable and it's distilled down to simply Opinion. Educated or not.

 

Regardless of all that, I agree that the best arbiter of sound Systems is our hearing mechanism, which includes the science of psychoacoustics in different ROOMS, the most expensive and Variable component next to our ears/brains.

 

I don't think that any Klipschead and frequent reader/poster here has an IDENTICAL system/room/amps/program material as you or I, or anyone else. When you throw in each respective hearing mechanisms and those of spouses or girlfriends, we have  further contributions to the UNIQUENESS of all things involved in the process.

 

All this boils down to individual OPINIONS with various preferences. Heck most of the people in this HiFi world don't like horns for various reasons.

 

Within the context and personal choice based on science and Opinion. After the evolution of system components and configurations for 55 years since I was an ignorant kid, I choose Amplifier Sonic Neutrality with lots of headroom over Low Output Power Inefficient Space Heaters with the Pleasant Euphoric Distortions of Tubes and Class A, which is what you and your wife, I suspect, discovered was missing from the sound you live with and got acclimated to when you heard the extremely Neutral Hypex NC technology.

 

But again, that's nothing more than my OPINION regardless of yours or other's here. But I do acknowledge and respect your choices in the quest for sonic nirvana. There is no wrong, only freedom of choice.

 

 

[ClaudeJ1]

8 hours ago, Langston said:

Analog audio components such as amplifiers have S/N ratios all over the map, but I aim for at least 96dB (16bit CD resolution). I have a Mark Levinson 532H that specs ">85dB" and a Benchmark AHB2 that specs 130dB. The latter sounds better and this may be part of the reason. (The Hypex NC400 measured in the 120's on my bench today)

Since power amp S/N ratios are rated at full output in a specified load, did you account for the full output differential of 6 db between the AHB2 and the NC-400?

 

And yes, having been a PWK fan since the late 60's, when I was a kid with a paper route.

 

I have historically told everyone that the less power your use, the less distortion you produce in a SPEAKER. Attributing this to IMD, for which,  PWK received an AES Silver Medal in the 70's.

 

However, you do get a funny look when you say "the fewer watts you use, the better it sounds" to the majority of people. HAH.

[ClaudeJ1]

20 hours ago, Langston said:

The output the NC400 is load-insensitive under 20kHz, another first for a Class D amp in my experience. I tinkered around with several APx515 measurements and the results were so good that I decided to turn everything off and plan what I'm gonna do. Plus the day is getting busy 'cause I just turned 62. : )

The fact that it's load insensitive is what makes it such a great amplifier for speakers with lots of passive components before the power reaches the drivers.

 

Not everyone is driving their voice coils directly, which is part of the chain of events.

[Langston]

13 hours ago, ClaudeJ1 said:

Since power amp S/N ratios are rated at full output in a specified load, did you account for the full output differential of 6 db between the AHB2 and the NC-400?

 

Nah, I was just throwing out a teaser based on the few measurements I made yesterday that showed me the NC400 was serious and required a planned measurement session. I drove the NC400 1dB shy of clipping (defined as 1% THD, 1kHz, 8Ω) and saw S/N numbers in the mid 120's. I was also using convenience outlets on my bench, when I do the real measurements I'll be using a dedicated 120V/30A and 240V/30A supplies.

 

I got the AHB2 S/N out of the manual and have never given it a full measurement run-through because I trust the designer so much. He's actually been one of my mentors in this stuff and (almost) everything I've ever fussed at him about concerning one of his products (the DAC3 phase via USB was a recent one), I got a polite slap-down and he'd walk me through the solution. On the (almost), I do want to submit for the record that I was right once a long time ago concerning the latency of the original DAC1. He used a bunch of math to calculate the serial group delays of every component in the system using mfg. specs for each part and I had a shiny new calibrated AP analyzer and, genius that I am, hit a button and measured it - Ha! : )

[ClaudeJ1]

5 minutes ago, Langston said:

I got the AHB2 S/N out of the manual and have never given it a full measurement run-through because I trust the designer so much.

I've been pondering the purchase of that amp based on it's incredible specs alone, and may still do so after you put the NC-400 to the Listening Tests.

 

My new horns (Driver Modded Edgar Titan II's) are in final stages of finishing. Since they are 6 db more sensitive than my upstairs setup, getting the AHB2 might be a great option. Even keeping in mind that their cost per watt is 8 Times that of the Hypex! Only needing 100 watts max. for 20 db peaks in the basement reduces the real cost to only 2X the Hypex.

[Langston]

9 minutes ago, ClaudeJ1 said:

I've been pondering the purchase of that amp based on it's incredible specs alone,

 

Benchmark will let you return the AHB2 after 30-days if you don't like it. "Risk Free" is BS 'cause you might keep it! : )

[Panelhead]

  The Benchmark AHB2 is way overkill. Thirty watts are plenty. But I think Class A/B with a resonant mode supply is a ticket to happy listening. Just not the only ticket. 

  Owned and built several Pass designed products. All seemed great. Some did not measure great.

[Shiva]

Nice back and forth discussion on this thread.   The Benchmark AHB2 is on the top of the amps tested list over at ASR.

 

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-benchmark-ahb2-amp.7628/ 

[richieb]

- and as I recall the nCore nc400’s were a very close second?