Choke power supply- part 2

Schiit audio will be coming out with mono block amps with choke power supplies. And will be over 60 pounds each. See picture # 5

https://www.schiit.com/products/loki-max

That fooled me for a minute, didn't realize I needed to scroll down on the pictures for Pic 5.  I'm really curious about this upcoming amp from Schiit.  They have been employing a lot of innovative circuitry(at least innovative to this guy) over the years in their headphone amps and dacs.

I'd not even heard about a choke power supply.  I passed on the Aegir amp, since it was only 20 wpc and wouldn't work with my speakers, and the Vidar has been better than my Adcom amps.

This new amp, I think they call it the "Tyr", I would really take a hard look at.  200 wpc, monoblock, they say it's the best sounding amp they've made.  I think I'd have to sell off the Adcoms...  

@daveyf ,

The first question would be do you know what a choke power supply is?

More accurately would be a choke filtered power supply, with a few different variants.

Why not?  Other than the cost and bulk, there is the question of whether they are the best implementation.

That said, most linear power supplies have some choke filtering, just for high frequencies.

Output of a bridge rectifier is DC + harmonics of twice the AC frequency. The choke in combination with the capacitor forms filter eliminating some of those harmonics, but the choke in combination with the load does as well. Hence, the output voltage can droop. So much for your high dollar, low resistance AC power cord.

To get enough inductance to be useful, you need a large inductance which means materials that are not great at high frequency. So at that point, do I really want the big inductor, or should I go for s smaller inductor and burn off a bit of power with a linear regulator? The best answer is always trade off the properties for the best overall implementation.

@cindyment  I hope you understand a linear power supply is to create a DC voltage and current out of a 60 hz AC line. One would not want it to pass high frequencies. The OP is posting about a choke input PS, which is considered to be a step above an ordinary supply using chokes and caps after rectification.

Whether you put the choke on the input or the output the effect is the same. A transformer reflects the impedance from one side to the other based on the turns ratio. Even if the inductor is on the front AC side, it still effectively forms an LC with the capacitor. Note Schiit's Description. It works, but is it is a good engineering idea? Questionable.  The "custom nickel core" sounds all impressive, but that is just common core material and custom inductor is not remotely difficult.

And pure LC—inductor-capacitor filtering from the highest to the lowest band, including 4 custom 80% nickel-core inductors as big as 1.5 Henries. 

Well apparently Schiit figured out a way to make it a "good engineering idea" without checking with cindyment.  Mike Moffat and Jason Stoddard have been designing/engineering amplifiers and dacs since the '90's, so they might know a thing or two about it.

And Pass amps use choke filters in their supplies too, but the question was why they are not more common, not whether they "can" work. I don’t need Mike Moffat and Jason Stoddard’s blessing for my comment and I expect across a table with engineers, their answer would not be much different from mine.

The fact it "impresses" you means it already "works", even if it does not make sense. It sounds really cool from a marketing standpoint. Choke regulation used to be common in linear power supplies.

I am not yet impressed as I haven't heard the amp yet, its not in production.  I am curious about the amp(as I said above), as I am curious as to why some try to find fault with something they haven't heard yet. If Pass Labs is doing it then its not like Schiit Audio is stepping out on a limb.   Have you heard any of their amps or other products?

Schiit Audio does almost no marketing, its part of their business model and partly why their products don't have stratosphere mark ups.  

The question was why are there not more amps with choke regulated supplies. Not whether you can make one work. I certainly did not question whether you could. I said there is little practical reason for doing it (beyond what I stated) and many practical reasons for not doing it.

Marketing is not just advertising, it is also how you present your products to market. Absolutely Schitt does marketing, they don't do a lot of advertising.

I seem to have misread @daveyf  question, and the responses of @cindyment are so inane, I had decided not to respond. But here goes anyway. All linear power supplies use a combination of chokes and caps after rectification to smooth the rectification pulses into a quasi DC output. The degree of ripple in that output is a consequence of the values of the components used. There have been choke input linear power supplies, which used to be used primarily in tube amps.

Charles Hansen used this type of choke input power supply in his Ayre V-1 and V-3 amps, but abandoned it for his later amps because of the high cost and weight penalties which would have made his products non-compeitive. You can google these amps for descriptions

It is inconceivable that someone would state that it makes no difference as to whether a choke is used before or after rectification.

IF Schiit has designed a new amp with maybe a choke input PS is not relevant until said product makes it to market.

Moffat is a wizard w ears and nickel in the transformer is expensive, get a quote….

i think it is great what Schitt is doing. The book Schitt Happened is excellent, especially the chapter by Mike…

I am a robot all choked up over part quality…

@oldears , you not understanding my responses does not make them inane.

What I said was:

Whether you put the choke on the input or the output the effect is the same. A transformer reflects the impedance from one side to the other based on the turns ratio

I did not say:

It is inconceivable that someone would state that it makes no difference as to whether a choke is used before or after rectification.

While the values are the same, the net effect w.r.t. choke regulation is the same. If you don’t believe me, work out a small signal model or simulate it. I assume you understand reflected impedance? To your point, when people talk about a choke regulated power supply, they usually mean larger inductors, than the typical minimum used for higher frequency harmonics of the AC line and noise. The transformer has enough bandwidth in this case to put a regulation choke on either side.

Your last post did not say anything I did not say already, I just put in more detail:

Output of a bridge rectifier is DC + harmonics of twice the AC frequency. The choke in combination with the capacitor forms a filter eliminating some of those harmonics, but the choke in combination with the load does as well. Hence, the output voltage can droop. So much for your high dollar, low resistance AC power cord.

.

The schematics above are 6 types of ways to do choke regulation. The big inductor after the bridge has wicked overshoot but eventually settles. Normally you put an element across the inductor. Note all the voltages are less than the capacitor alone. That is the load dependency issue with choke supplies. The one that overshoots a little and then settles fast with little ripple is a hybrid of inductance before the transformer and after the bridge. Hybrid approaches are best.

Sorry it is hard to read. Not the easiest editor with embedded images.

If you really want to learn more a about choke applications in power supplies find yourself an amp tech that worked on Fender amps from the 40’s and 50’s when Leo was going for cleaner and cleaner tone. Short story to effectively use choke tech I t requires massive high quality transformers which is a cost and supply chain issue. Unless you take the McIntosh approach and produce them in-house.

We use chokes in our designs more expensive well yes a resister can cost $0.99.  I have seen preamps that use a resistor to stabilize power.  But the average person here does not have a clue.