Review and Measurements of NuForce STA-200 Power Amp

[graz_lag]

I looked at Job 225 specs/website before finishing this review. They show the same poor distortion metrics as I got/NuForce advertises. So they are no better in this regard.

Hi :

Ferrite cores, ferrite beds & THD ...

Today, I have been asking to an engineer I know, who's working in the R&D of a French company (Atoll) that makes amplifiers and DACs, his opinion.
He told me they were experimenting with ferrite AC filtering but they did not like it.
The sound was "contaminated" with some kind of grunge effect (I am sorry for the Nirvana ... Soundgarden' fans in here ...)
They faced magnetic buildup within the cores, and that was degrading the quality of sound over the time.

Going back to the class D amplifiers and THD, he's forwarded a technical document, which I would like to share.
Pls. see the attachment : Predicting the Impact of Magnetic Components Used for EMI Suppression on the Base-Band of a Power Amplifier

It details researches conducted by a French team in 2016 ... with some very interesting discoveries ...

 

[restorer-john]

t details researches conducted by a French team in 2016 ... with some very interesting discoveries ...

An interesting link and read. Thanks for posting it.

I can't help myself. I scavenge ferrite toroids, EMI clamps off power leads, laptop SMPS DC ferrite clamp feeds, even the ferrite used over ribbon cables, when I strip stuff. You can make up trigger transformers, filters and all sorts of 'fun things with ferrite'.

 

[Sal1950]

I can't help myself. I scavenge ferrite toroids, EMI clamps off power leads, laptop SMPS DC ferrite clamp feeds, even the ferrite used over ribbon cables, when I strip stuff. You can make up trigger transformers, filters and all sorts of 'fun things with ferrite

John, maybe you should consider a 12 step program?

"God, grant me the serenity to accept the things I cannot change,
Courage to change the things I can,
And wisdom to know the difference. "

 

[bigx5murf]

I wonder if this thing would perform better if there was a way to lower the gain setting.

 

[boded]

Interesting that they state "designed by ear", and have the distortion dominated by 2nd harmonics. I don't think that is an accident. Very interesting presentation by Nelson Pass at San Francisco's Burning Amp Festival where he explained the effect on perceived sound in the room with addition of 2nd harmonic distortion to a musical signal.

 

[graz_lag]

Interesting that they state "designed by ear", and have the distortion dominated by 2nd harmonics. I don't think that is an accident. Very interesting presentation by Nelson Pass at San Francisco's Burning Amp Festival where he explained the effect on perceived sound in the room with addition of 2nd harmonic distortion to a musical signal.

... The even harmonics provides the complex, warm, rich sound that so many musicians (guitarists most of all) desire ...

 

[boded]

And it goes further than "warm and rich". See the Nelson Pass interview on Stereophile website "Circuit Topology and the End of Science". He is, of course, an excellent engineer, who also does measurements, but has a knack for stimulating people's thinking.
"We floated some prototypes around and found that most people preferred a particular setting. There was a consistent subjective observation that there was a difference not only with the level of second harmonic, but phase also. Negative-phase second harmonic tends to expand the perception of front-to-back space in the soundstage, separating instruments a bit. Positive phase does the opposite, putting things subjectively closer and "in your face." I have heard this sort of comment from people who were not in a position to have expectation bias, so I treat it seriously."
Read more at https://www.stereophile.com/content...gy-and-end-science-page-2#j49zyqDLA1PcIGrb.99

Since people are trying throughout the playing/recording/mixing/mastering/listening chain, where some type of distortion is added at every step, to create a sense of realism of the instruments in your listening room, understanding the subjective perceptions of distortion becomes interesting.

 

[Sal1950]

Interesting that they state "designed by ear", and have the distortion dominated by 2nd harmonics. I don't think that is an accident. Very interesting presentation by Nelson Pass at San Francisco's Burning Amp Festival where he explained the effect on perceived sound in the room with addition of 2nd harmonic distortion to a musical signal.

Bob Carver played this game years ago. After the famous (infamous) Carver challange at Stereophile, Carver started producing a line of amps "designed by transfer function tuning" to sound exactly like some very expensive tube amps. These amps were part of his successful mainstream marketing for a number of year after.
https://www.stereophile.com/content/carver-challenge

 

[maxxevv]

And it goes further than "warm and rich". See the Nelson Pass interview on Stereophile website "Circuit Topology and the End of Science". He is, of course, an excellent engineer, who also does measurements, but has a knack for stimulating people's thinking.
"We floated some prototypes around and found that most people preferred a particular setting. There was a consistent subjective observation that there was a difference not only with the level of second harmonic, but phase also. Negative-phase second harmonic tends to expand the perception of front-to-back space in the soundstage, separating instruments a bit. Positive phase does the opposite, putting things subjectively closer and "in your face." I have heard this sort of comment from people who were not in a position to have expectation bias, so I treat it seriously."
Read more at https://www.stereophile.com/content...gy-and-end-science-page-2#j49zyqDLA1PcIGrb.99

Since people are trying throughout the playing/recording/mixing/mastering/listening chain, where some type of distortion is added at every step, to create a sense of realism of the instruments in your listening room, understanding the subjective perceptions of distortion becomes interesting.

How would the "Negative Phase second harmonics " look like in instrumentation measurements from a purely layman's perspective of things ?

Do they show up as being in opposite phase to that of the prime test signal ( example 1khz ) in the FFT measurement graphs ?

 

[HammerSandwich]

Herb Reichert writes about Burning Amp & the Pass H2 circuit in his latest column.

 

[maxxevv]

Herb Reichert writes about Burning Amp & the Pass H2 circuit in his latest column.

Have the so called subjective observation results been remotely duplicated?

He doesn't go into details on how it shows up in instrument measurements either ?

 

[amirm]

Interesting that they state "designed by ear", and have the distortion dominated by 2nd harmonics. I don't think that is an accident. Very interesting presentation by Nelson Pass at San Francisco's Burning Amp Festival where he explained the effect on perceived sound in the room with addition of 2nd harmonic distortion to a musical signal.

I have yet to see such things confirmed in controlled testing. In every case of high distortion, I have failed to hear anything positive. The effects are either inaudible, or slight degradation of high-frequencies (due to additional harmonics they get higher pitched), distortion of bass and loss of some detail because of it.

For distortions to be readily audible as such, it would need to be of considerable amount, not just a fraction of percent.

 

[RayDunzl]

How would the "Negative Phase second harmonics " look like in instrumentation measurements from a purely layman's perspective of things ?

Sample Waveforms, Sine at 0.5 and harmonic at 0.25 amplitude. The harmonic starts at the same time (in-phase) or starts at the same time with inverted polarity (out of phase).

Frequency analysis would look the same, because the same frequencies are present at the same levels irregardless of phase during the measurement window (I think)

Let's see:

2nd in-phase or inverted looks like this:

Other software would be able to display the phase of the harmonic in addition to the level.

REW has that capability in the RTA window.

Do they show up as being in opposite phase to that of the prime test signal ( example 1khz ) in the FFT measurement graphs ?

Not in the above display.

Now sending the tones to REW.

In-phase 2nd harmonic

An the inverted:

 

[andrewinukm]

I happened to own quite a few things that was measured here.

D50 (bought it due to the hype here. It sounds really good).
DAC DAC HS (as an upgrade to D50)
Nuforce STA200

No measurements as I don't own any measurement stuff. But in my home, D50 with STA200 cause audible hum on the speakers. Ground loop? Mains contamination? I can't tell.

The DAC DAC HS with STA200 is silent.

And also I'm a tweaker. I do all sorts of tweaks that drives measurement/objective guys to rage.
Despite the measurements, I cannot n
agree that the Nuforce performs poorly from listening point of view.

Also, the ISO Regen that was thrashed and made a big deal about, it absolutely has a significant audible effect on sound of D50, which to me (and many of my visitors) is an improvement.

I guess besides measurement, you just gotta be curious enough to try some stuff to know for sure. I love the measurements, but listening ultimately makes the decision.

 

[Sal1950]

Also, the ISO Regen that was thrashed and made a big deal about, it absolutely has a significant audible effect on sound of D50, which to me (and many of my visitors) is an improvement.

What were the conditions under, and statistical outcome of your bias controlled blind listening tests?

 

[andrewinukm]

What can I say: it was in my room, using my audio setup. It's barely controlled (if at all). Read my description again: it works in my system. And the observation is significant enough, that I can confidently say it has an effect (i did not say good or bad. Wonder why measurement guys goes all excited if an effect is deemed negative, but goes indignant when the effects are deemed positive... when in fact the measurement data shows that it should not have an effect. Any effect only serves to prove them wrong.). If only you were here, I am confident that you would agree.

I don't own any measurement devices. Let's never forget this: I (and others) am a consumer just like you. So I'm not here to sell. I'm just here to share and hope to figure out the correlation between measurements and my individual listening observations... and maybe discover why good measurements sounds good, why some bad measurements also sound good, and why some unexplainable tweaks can change a sound. (Yes I've heard enough of these: some has an effect, some don't. And I'm objective enough to admit it when I made bad decisions buying something that i can't hear a difference. And objective enough to admit it that my scientific mind is boggled when I can hear an effect.) I have some background sensory analysis. In food testing, different tests equipments measures different aspects, and they are unable to measure everything that humans can sense. It is important do conduct trials using human's senses as measurement tools.

Also, you guys do realise that doing blind tests with sufficient confidence level and robust statistical outcome requires a lot of work, planning, time, and resources? And that it is close to impossible for most people to do them well in a home environment. I hope whenever a person demands for DBT/ABX trials, he/she has some sort of decency to be respectful, even if an individual is just conducting a simple non-controlled basic test.

If you guys are dead set on some crazy controlled experiment designs, I'll dig up my old notes on sensory analysis and figure out some kind of single blinded tests and controlled bias with maybe 20 screened test subject (10 expert testers, 10 non-experts), conducted over a period of 6 months (not easy to gather people all at the same time). No need for double blind, it's a home test for internet forums, not medical research.

Anyway, here was a simple NON CONTROLLED, test I did to determine if I was crazy that I heard a difference (I consider the differences an improvement considering that it sounds better, and I like it). It wasn't done to fulfill objectivists' undying need for the perfect test. <-- keep this in mind before anyone starts running around with pitchforks test probes screaming blasphemy against measurement gods.

Objective: To determine if addition and removal of ISO Regen in owner's hifi system produces observable difference in sound to-be-heard by other audiophiles.

Test subjects/evaluators: 4 semi-expert evaluators (audiophiles age 18-35 who listen using high head-fi equipments.)

Gear setup:
Laptop (Foobar) > Supra USB cables 2m > ISO Regen > USPCB ultra short USB cable > Topping D50 > Audience Ohno IC > Nuforce STA200 > Audience Ohno cables > Audience The One V2 speakers.

Experiment design:
Sighted test.
Simple A-B-A test methodology.
Subjects purpose of visit is to listen to music through speakers and check out other audio stuff, it just so happened I also own the ISO Regen.
Subjects take turn to sit in the sweet spot.

1. Start with full setup with ISO Regen in the chain. Listen to music.
2. Remove ISO Regen. Listen to music for the 2nd time.
3. Insert back ISO Regen. Listen to music for the third time.

Results:
All evaluators heard a difference when ISO Regen was removed (Step 2). The level of observable difference being easily observable and heard, casual listening is sufficient to hear the difference.
All evaluators heard a difference when ISO Regen was inserted back (Step 3). Level of observable difference is similar as step 2.

3 evaluators prefer the sound with ISO Regen in the chain.
1 evaluator prefer the sound without ISO Regen in the chain. However, he noted an increase in clarity and "better/more precise" sound stage with ISO Regen, but still prefers the warmer and "less precise" sound without ISO Regen.

Statistical analysis: None. Number of test subjects/evaluators are too small, and the investigator was lazy and incompetent.

Discussion and conclusion:
The owner of the system and investigator (yours truly) is happy with the result, knowing that he is not the only crazy individual that he heard a significantly observable difference with the ISO Regen. Objective of experiment is achieved.

Disclaimer:
I'm all for science and measurements, but I also prefer to spend my time listening and enjoying music, and conduct tests according to my convenience and whims. Most guys do not have any idea regarding the scientific methods of sensory analysis, so these individuals really shouldn't run around shouting about DBT and controlled testings, and recognise that an individual observation is also useful data. In medical world, individual case reports of unusual observations are also treated as important data, even if it could not be explained scientifically. If one is to have a truly objective mind, no data is rejected without given due process in thought and analysis. Even outlier(s) has to be explained. And if there are sufficient outliers that are consistent, these outliers become a common phenomena that needs to be analysed without bias by the investigator, and not with a prejudiced mind assuming placebo being the only possible explanation.

 

[amirm]

1. Start with full setup with ISO Regen in the chain. Listen to music.
2. Remove ISO Regen. Listen to music for the 2nd time.
3. Insert back ISO Regen. Listen to music for the third time.

Results:
All evaluators heard a difference when ISO Regen was removed (Step 2). The level of observable difference being easily observable and heard, casual listening is sufficient to hear the difference.

This is easy to replicate and observe with any audio device/tweak regardless of efficacy. Even though I am fully aware of what causes it, I can still fall prey to it. And easily so.

The example I use is playing the same piece of audio file multiple times. I guarantee that in every playback cycle, if you focus, you will hear difference in fidelity even though you have changed absolutely nothing! You don't have to have an expectation of difference to hear a difference. And knowing what I just told you is not sufficient to not hear it!

The brain works differently when it is analyzing fidelity between pieces of audio/instances. It is that difference that causes your observation, not what the device did or did not do. Until such time that you conduct a single controlled test to see how reliable your observations are wrong, you are just feeding yourself junk conclusions.

I don't expect any of this to make sense to you as the level of conviction in your testing is so strong. You will have to be forced into that controlled test at least once to realize the error in that.

 

[Sal1950]

And if there are sufficient outliers that are consistent, these outliers become a common phenomena that needs to be analysed without bias by the investigator, and not with a prejudiced mind assuming placebo being the only possible explanation.

But yet you insist that you have no time to insert any real controls over your listening experience since it is only for enjoying music. How do you expect to be taken seriously on a science based forum when you will go no further than "I hear it so it is so". I have no time to debate with someone that refuses to participate in or produce any verifiable evidence for what he "thinks" he hears.

 

[andrewinukm]

This is easy to replicate and observe with any audio device/tweak regardless of efficacy. Even though I am fully aware of what causes it, I can still fall prey to it. And easily so.

The example I use is playing the same piece of audio file multiple times. I guarantee that in every playback cycle, if you focus, you will hear difference in fidelity even though you have changed absolutely nothing! You don't have to have an expectation of difference to hear a difference. And knowing what I just told you is not sufficient to not hear it!

The brain works differently when it is analyzing fidelity between pieces of audio/instances. It is that difference that causes your observation, not what the device did or did not do. Until such time that you conduct a single controlled test to see how reliable your observations are wrong, you are just feeding yourself junk conclusions.

I don't expect any of this to make sense to you as the level of conviction in your testing is so strong. You will have to be forced into that controlled test at least once to realize the error in that.

Please note that the comments from the evaluators were: the difference is easily observable even with casual listening without focused listening. Yes, the effects are that strong that single blinded test are redundant. Blinded testing is only required if the effects are too minimal, and require being "blind" to control the conditions and bias.

I understand if a difference is minute or non-existance, every time a person does a repeat listening, it is bound to hear something. I've experienced it myself, and am aware of this happening. So if I "think" I hear something, i go back and forth repeatedly to verify. Usually it ends up beign concluded that the difference is non-existent or too minimal for me to observe and therefore not meaningful to me.

But sometimes, some differences are very observable. This is the reason I'm reporting it here. If it weren't, I would've gotten rid of it, like I did with the iPurifier (V1), JitterBug, & W4S Recovery which I no longer owned. These products got pretty good reviews elsewhere, but nope they ain't doing nothing for me, even when I was biased to hear an effect.

 

[andreasmaaan]

Blinded testing is only required if the effects are too minimal, and require being "blind" to control the conditions and bias.

No, blind testing seeks to ensure that perceived differences - whether minor or drastic - are a result of real differences, as opposed to extraneous psychological factors.

There is no rule that says these extraneous factors only ever result in minor (as opposed to drastic) perceived differences, nor any evidence to support this view.