NS2 humming power supply

[pterm]

It would be a mistake to use a transformer-less power supply. If you look at high-end audio equipment they all use transformers. The circuit is simple to get clean DC using a transformer. AC in goes through an AC line filter, then to the transformer which provides electrical isolation and steps down the voltage, then to a bridge rectifier with snubbing capacitors to reduce the switching noise, then through filter capacitors to reduce any AC ripple, then to a voltage regulator. If you want the safest, most reliable, and lowest electrical noise power supply you use a transformer. Everything I have read in electronics have said that the only reasons transformer-less power supplies are used is to reduce cost and weight. They are inherently unsafe and electrically noisier. See "The Art of Electronics Third Edition" by Paul Horowitz and Winfield Hill.

I did some further reading on "tranformerless supplies" and I agree with what you say. --I used the term in error not realizing the it refers to the cheap, non-isolated supplies you mentioned. What I meant, when I used the term (incorrectly) was a supply without a transformer operating at mains frequency.

Thanks for setting me straight on the correct usage of "transformerless" and for bringing the third edition of H&H to my attention. --I only have the second edition of Horowitz and Hill. What is the name of the chapter addressing transformer-less supplies - it's not specifically mentioned in my Index, but I am interested to read what they say.

I strongly believe a better technical solution for Nord is to get rid of the AC-mains-frequency transformer. Although this kind of transformer provides a reliable and simple supply, it operates in the audio band. Subsequently, the transformers can leak magnetic fields in the audio band and produces audible hum both of which many on this forum find objectionable.

Better more modern solutions exist: If it interests you, look at AC-DC power conversion from Vicor. --Vicor design and builds military, aerospace, medical, and telecoms power supplies.http://www.vicorpower.com/files/live/si ... iagram.jpg They first rectify and filter the AC to produce high-voltage DC then use a controller to switch the high voltage DC through a transformer (at high frequency - out of audio band) to achieve isolation from the mains and step the voltage down as needed.

Does Nord need an aerospace-grade solution? No.
Do I think disassembling the instrument, flipping a switch and changing the fuse to change input voltages is acceptable in a professional instrument? No.
Do I think a mains-frequency transformer inside a high-end musical instrument is a design choice that needs reconsideration because of the audio and electromagnetic noise and extra weight? Yes.

Do I want to see Nord make their keyboards even better? Yes.

[stuartoMVF41000S]

If you want. However I would quote one of the following below. Note that Nord could get rid of the audible mechanical noise of the transformer, but doing so would increase their cost which would result in us paying more. Since the mechanical noise is not something that enters the electrical audio signal I imagine that is why they don't bother with it. The Fairchild Semiconductor document explains how it can be done. :

www.keithley.com/data?asset=57120
or
https://www.fairchildsemi.com/applicati ... N-4148.pdf

[stuartoMVF41000S]

In answer to where in the 3rd edition is the topic on transformer-less power supplies: section 9.5.2 with the heading "transformer".

With respect to Nord's implementation in the NS2 notice that the power supply is it's own unit placed away from the audio circuitry. Just by locating the transformer away from the audio circuitry provides the major portion of the solution. They enclose the transformer in a faraday cage to reduce the stray magnetic fields. Note that the size of the magnetic fields is directly related to the size (power rating) of the transformer.

[pablomastodon]

Wow...this is like watching Clash of the Titans.

Please note, however, that the perforated bit of metal encasing Nord power supplies is not really a Faraday cage. Some US govt or other regulatory agency decided that those power supplies are dangerous because someone might touch something and zap themselves (never mind that a dozen or so screws first need to be removed to get into the chassis) and began requiring the cage as a safety measure. Typical dumbass US govt stuff. But a true Faraday cage would be a bit more involved, and probably a lot more expensive.

Bless,

Pablo

[pterm]

I wondered about that cage: The pictures I saw showed it didn't fully enclose the supply, giving it dubious shielding value... So the safety explanation makes a lot more sense!

Regarding, "Clash of the Titans", I think you refer to the 1981 Laurence Olivier film with the (cheesy) stop-motion special effects. In which case, I think I should be mildly insulted. We need to add a "mildly insulted" button next to the "thanks" button.

[pablomastodon]

Movie references are sometimes part of my vocabulary, but not in this instance. I have a very vague recollection of that Sir O pic and can well understand feeling offended by that comparison, but that's not what I had in mind. How he ever got involved in that mess was a mystery. I think Sir John Gielgud has a similarly awful movie credit late in life...

But when the 2nd edition of H&H got trumped by the 3rd edition of H&H...well, it was just fascinating to read.

Bless,

Pablo

[ConMetz]

It is good that Nord will move to a power supply without a transformer. Audible noise and electromagnetic noise are important design criteria for electrical equipments.The hum you are hearing is from the internal power supply, it comes from the transformer that is situated on the power supply PCB. It is an entirely acoustic thing; this hum does not reach the audio signal in any way, as you have found out. The hum is normal and does not indicate a fault or an upcoming problem.

[Whythedamnhum]

Why waste time? Too many competitors are capable of a noise free, top tier keyboard which Nord is not. Hello Yamaha, Korg etc.... I’m your new customer.

[23skidoo]

Actually, Korg and Yamaha, among many other vendors' power supplies, especially the wall-wart kind, can hum quite a lot if you put your ear up to them. Not all models, not all units, but a good many. It's a normal thing and the fact that anyone thinks this is specific to Nord shows either their inattentiveness or lack of broad experience.

Power supplies are essential components to high end audio, and you'd be surprised how many make audible mechanical noise, despite being perfectly silent electronically.

@pterm: regardless of where Nord puts their transformer, you'll carry the weight anyway. I'm far from alone in saying that an internal power supply is basically the highest-end way to go for a keyboard manufacturer. It's basically an industry standard and if a keyboard requires an external power supply even the SOS editors, for instance, point it out as a defect/con against it.

The reasons are obvious: an external supply is more vulnerable to damage, more likely to be lost or forgotten, and less easily replaceable in either case as it's unique to the keyboard it supplies. An internal supply is the most protected and impossible to forget or lose. Thus, it leads to a much more reliable total system, fewer awkward items to carry/pack on the road, and a power cord that's internationally standard and trivial to replace anywhere in the world if lost or damaged. In addition, the total system weight is actually lower since you don't need a separate secondary enclosure for the power supply. Nord is doing the right and proper thing building their power supplies into the boards.