Hypex NC400 - DIY Mods

[Feyire]

If this is true, then grab a mic & REW and record some Frequency Sweeps with the fuse in one position and then the other position and show us how the bass increases in the measurement plots. Should be pretty straightforward experiment.

I never claimed there was an audible increase in the bass output, only that one way sounded different/better vs the other. As such, I don't expect frequency sweeps to yield any meaningful/useful differences, but that is not to say I wouldn't try it.

My suspicions are currently aimed at possible phase and/or group delay differences (caused by the fuse and/or including room modes). We already have good research on these forums (Audibility of group delay at low frequencies), showing that this can cause audible differences at low frequencies (i.e. bass).

 

[fpitas]

I for one look forward eagerly to our deeper understanding of the electrical characteristics of a fuse.

 

[AdamG]

I never claimed there was an audible increase in the bass output,

The difference was only noticed in the bass frequencies

But that is exactly what you said. So if there is indeed a Noticeable difference in Bass frequencies it certainty can be measured. Back to you. I can play this game all day but in the end. It remains your responsibility to prove your claims. Trust but verify is what ASR is built upon and you have been here long enough to know that.

 

[tuga]

I suppose the only answer for this is also - measurements!

Modding without measuring makes little sense, even if listening perception / audibility is important.
It's like making changes to your race car, driving it for a few laps and saying "it's driving better and faster" without actually timing your laps to determine if that is the case...

 

[Feyire]

But that is exactly what you said.

That is your interpretation of what you think I meant, when I said a "...difference was only noticed in the bass frequencies...". I'm sure you'd agree that what I said was somewhat vague, and can be interpreted in different ways, as there are many factors that can contribute to a perceived difference in sound, other than just loudness (i.e. "..show us how the bass increases.")

As such, let me try to qualify more precisely what I heard, because my girlfriend and I never noted a loudness difference during the listening sessions.

So if there is indeed a Noticeable difference in Bass frequencies it certainty can be measured. Back to you.

I agree that if a difference exists, it should be quantifiable.

As I said previously, I'm leaning towards phase and/or group delay differences/changes being a potential contributor. Frustratingly, the difference I heard is difficult to put into words, hence the somewhat vague description given previously. So for one particular way, the bass sounded correct and appropriate (e.g. you know a particular song and have heard it multiple times on different equipment and know what to expect in terms of bass), whereas the other way just sounded incorrect and messy, as if the bass timing/phase was completely off.

 

[AdamG]

That is your interpretation of what you think I meant, when I said a "...difference was only noticed in the bass frequencies...". I'm sure you'd agree that what I said was somewhat vague, and can be interpreted in different ways, as there are many factors that can contribute to a perceived difference in sound, other than just loudness (i.e. "..show us how the bass increases.")

As such, let me try to qualify more precisely what I heard, because my girlfriend and I never noted a loudness difference during the listening sessions.


I agree that if a difference exists, it should be quantifiable.

As I said previously, I'm leaning towards phase and/or group delay differences/changes being a potential contributor. Frustratingly, the difference I heard is difficult to put into words, hence the somewhat vague description given previously. So for one particular way, the bass sounded correct and appropriate (e.g. you know a particular song and have heard it multiple times on different equipment and know what to expect in terms of bass), whereas the other way just sounded incorrect and messy, as if the bass timing/phase was completely off.

We’re not playing “Dodgeball”.

Everything you eluded, hinted, vaguely recall and maybe kinda might have heard in phase, timing, correctness, incorrectness or on the messy scale. Should be evident in a FR sweep measurement. You are now Dancing around and attempting to distract us or walk back your initial claims. This WILL be your last chance to either put up (Measurements) or admit that what you heard/experienced is not provable via the use of Science or Engineering techniques. Another words, you heard what you expected to hear (expectation bias) when flipping a bi-directional circuit (fuse) orientation.

These are the type of claims that they will lap up like fresh milk in a dog bowl at a plethora of Subjective Peter Pan type Audio forums. This is ASR and that Subjective Dog don’t Hunt here. Prove it or admit that some form of human bias was at play and you experienced a type of psyoacoustic behavior that is not factual. The Science of electrical fuses are omnidirectional and their orientation is irrelevant. I think we’re done here.

 

[capslock]

About the output inductor and caps, as has been pointed out, they are in the feedback loop, so whatever nonlinearity they exhibit should be attenuated (not eliminated) by feedback. The caps are just a high frequency shunt to ground, so I am not much worried about them. At < 20 kHz, the impedance of the coil is still low, and there is plenty of loop gain to correct anything they do. Replacing them in a way that they are twice as high could also be called making a bigger antenna...

The output coil probably uses the ferrite core and cage mainly for EMI screening. The inductivity enhancing effect of the ferrite is probably not much needed here, as a pure air coil is similarly small (20 mm dia., 20 m length and 27 turns will give you 10). Using a large copper foil inductor is a bad idea for several reasons:
- again, it is physically huge, meaning it acts as a radiating and receiving antenna
- there will be a strong magnetic field from the coil axially
- the copper foil design has a much higher shunt capacity than a single layer, solid wire air core inductor, meaning it does not do its job of attenuating HF switching noise properly.

Since the existing ferrite core is probably not magnetized much, I wouldn't worry so much about its nonlinearity as a function of current. However, purists might be afraid of Barkhausen noise that, similar to Class B crossover distortion, will be highest when the magnetization of the core switches from one orientation to the other. So if one really wanted to use an air core inductor, a single layer air core toroidal is what I would try.

About the unidirectional fuse, I am still speechless. There is nothing in the cited notes from the manufacturer to indicate that the construction is directional, nor does AC current have a direction. There is a small effect I might concede: I did measurements on a SMPS1200 https://www.diyaudio.com/community/threads/hypex-smps1200a400-measurements.358972/, and there is quite a bit of rectified 50 Hz noise evident on the secondary. Getting rid of one of two fuses in series or using a low resistance fuse will slightly change this noise, but changing your power cord or using a different outlet in your house will too. Actually, lower resistance is potentially worse here.

 

[john65b]

Sorry to add to this craziness, but I find it odd that you quote and appreciate the vast knowledge Bruno Putzeys and Douglas Self.

If Bruno and Mr. Self had told you that this special Directional Fuse is nonsense, would you then believe what you are being told here? I bet they would agree.

I had a girlfriend a long time ago that believed Cunalingus was performed on a man. I asked her if we could look it up, together, in the dictionary. She refused, saying it was me that needed to read up on it. I wonder where she is now.... nah... no I don't.

 

[goryu]

This op sounds like that tweak nut job Ric Shultz who advocated the same mods to the nc400 and other class d Hypex/Purifi amps, along with a host of other snake oil nonsense.

 

[Feyire]

This op sounds like that tweak nut job Ric Shultz who advocated the same mods to the nc400 and other class d Hypex/Purifi amps, along with a host of other snake oil nonsense.

Ric did indeed provide the basis for most of the documented modifications. I consider myself quite fortunate to have come across his work.

In fact, as of April this year, it will have been 3 years since I modified my NC400s, and I am still happy to report that the modified amplifiers are working fine and sounding great.

It is a shame that there hasn't been more NC400 owners curious to try the modifications, in particular the LC output filter changes, as these provide the most significant and most audibly evident difference.

About the output inductor and caps, as has been pointed out, they are in the feedback loop, so whatever nonlinearity they exhibit should be attenuated (not eliminated) by feedback.

The hysteresis distortion caused by the ferromagnetic inductor and the ferromagnetic leads of the output capacitors would indeed be attenuated by the feedback.

Which is why one of the goals of the LC output filter modification is to completely eliminate the source of the hysteresis distortion originating from these components, by replacing the ferromagnetic inductor with a pure copper inductor, and by replacing the ferromagnetic leads of the output capacitors with copper leads.

If as you say, purists care about barkhausen effect/noise, well they then should also care about eliminating sources of hysteresis distortion.

The caps are just a high frequency shunt to ground, so I am not much worried about them.

There is a benefit to gain, in terms of noise reduction, by ensuring the caps are placed so that their outer foil is facing towards ground.

The caps used in the NC400 don't have external markings to indicate where their outer foil is located, so there is no guarantee that the caps will be installed in a way to guarantee lowest possible noise when assembled in the factory.

 

[goryu]

It is a shame that there hasn't been more NC400 owners curious to try the modifications, in particular the LC output filter changes, as these provide the most significant and most audibly evident difference.

Please show the improvements in the measured performance. If if is audible, you can measure and post.

There is a benefit to gain, in terms of noise reduction, by ensuring the caps are placed so that their outer foil is facing towards ground.

Show us the before and after measurements. Again, if there are audible noise reductions it should be quite simple to show us the measured improvement. Also, please explain the science behind the outer foil orientation having an audible effect.

It bears keeping in mind that many of Tweakie's "mods" may well change the sound of a piece of equipment. What he has been asked repeatedly, and has never been able to prove, is that despite all of his hyperbole about "taking the _____ to an 11" with his mod of the day, he has never ONCE shown a measurable improvement in ACTUAL performance. In fact, he goes on and on about how none of his tweak "improvements" can be measured! Something that does nothing to improve the measured performance is not an "improvement", it is a difference. And whether or not a difference is an "improvement" is a subjective matter of opinion, not a factual increase in real performance. In most cases, his flailing about with Bruno's work is like having 3 year old taking a marker to the Mona Lisa, adding a mustache, and calling it an "improvement". In fact, most of his mods in all likelihood DECREASE the actual performance of his victim's equipment. His "work" is more akin to audio vandalism.

 

[CleanSound]

I have no idea how I stumble across this thread. . .but it's one bizarre thread.

I assembled a dual mono NC400, it sounds great out the box and it measures great.

It befuddles me that someone thinks they can modify this fine piece of engineering to gain more audible benefit since this amp measures below the hearing threshold for most animals on planet Earth, maybe except a bat.

 

[SIY]

Ric did indeed provide the basis for most of the documented modifications. I consider myself quite fortunate to have come across his work.

That is absolutely hilarious.

 

[AdamG]

That is absolutely hilarious.

And on that note. I think we can stick a fork in this thread…