Author Topic: How important is Power Supply Design?  (Read 3288 times)

Offline Nick B

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Re: How important is Power Supply Design?
« Reply #30 on: September 07, 2018, 04:59:35 PM »
Ok, it was good and quite informative while it lasted. Iím not able to make any judgments on whoís right or wrong as the technical discussion is way above me. What I do know is that Steve is an accomplished designer and Folsom makes great sounding products according to Dave, whose ears I trust and whose Uber I love. And then thereís Gary who loves diy and whose cables I use and they sound really good. So my final words are ďpacem in terris ď or Iíll lock the thread
« Last Edit: September 07, 2018, 05:01:08 PM by Nick B »
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Offline rollo

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Re: How important is Power Supply Design?
« Reply #31 on: September 10, 2018, 10:45:08 AM »
   Boys boys play nice. Yes known laws dictate the basics, but but sometimes different approaches within the laws render different outcome.
   We cannot become so ruled by law that we cannot imagine. We would not go forward if we did. All I know changing a cap in the power supply gives me a different sound.
   Give me a better PS and I'll give you better sound. John Lennon "Imagine"

charles
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Offline P.I.

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Re: How important is Power Supply Design?
« Reply #32 on: September 10, 2018, 10:54:50 AM »
   Boys boys play nice. Yes known laws dictate the basics, but but sometimes different approaches within the laws render different outcome.
   We cannot become so ruled by law that we cannot imagine. We would not go forward if we did. All I know changing a cap in the power supply gives me a different sound.
   Give me a better PS and I'll give you better sound. John Lennon "Imagine"

charles
+1  on everything.

Give me a crappy linear power supply and I'll give you back a much, much better one.  Ain't gonna be the be all and end all, but it will certainly sound a lot better than stock.

Saw this thread take a left hand turn and pretty much decided then to not stoke the fire.   :roll:
"A man with an experience is never at the mercy of a man with an argument." - Hilmar von Campe

Offline steve

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Re: How important is Power Supply Design?
« Reply #33 on: September 10, 2018, 07:49:05 PM »
Hello Everyone,

Let me first state that it is amazing how good the sound is when a truly great power supply design is used. Anyone can get pretty good sound by being off on their power supply design, and pretty good is what you'll get. Getting the best is another matter. It is not as simple as just switching to poly caps etc. One has to consider the entire design.

It seems that my white paper was a bit too complicated, so I will start at the beginning and go step by step and prove the power supply decoupling capacitor not only handles musical signal current, but also alters the frequency response of an audio stage.

I will even do most of the mathematics, but I will also provide the equations in case one is interested. I will use a series of figures to help.

For those who wish to skip the points below, and get a quick summation, the points below prove that power supply  filter capacitor (C1) is in series with RL, so actually RL + C1 (AC resistance/capacitive reactance Xc). Since Xc is frequency dependent, RL + Xc changes with frequency, and the gain of the stage is frequency dependent, so the frequency response is not flat.

Since RL has AC musical signal current flow, C1 does as well; in fact some 15 or more times Ccoupling capacitor and Rg in my example.

C1 capacitor also has AC voltage, musical signal voltage on its positive terminal. All these can be easily measured so they follow the laws of electronics.
Thus my white paper is correct.

For the rest of us, relax, take your time, and letís get started. At the bottom of this post are Figures A, B, C etc. I also provided them in .pdf format at the very bottom in case some prefer .pdf.

Here we go.

1.   Figure A is simply a 10 volt DC battery with a 10k ohm (10,000 ohm) load resistor, resistor placed across itís terminals. 1 ma (1 thousandths of an ampere) current flows through the resistor. The equation is: Current = voltage divided by resistance.
I = E / R

2.   Figure B is a 10 volt AC source with a 10k ohm load resistor. Again, 1 ma. of AC current is also flowing through the resistor. The same equation as point 1. This applies for whatever audio signal; 60hz, 1,000hz, 10,000hz are examples of AC, or a musical signal.)                     

3.   Next, Figure C is the same 10 volt AC source with a 10k ohm load resistor. However, I divided the 10k ohm resistor into a 4k ohm resistor Rp connected in series with a 6k ohm resistor RL. Again 1 ma. of current flow. I = V / R. The output AC voltage is calculated: Output = 10 volts x (6k / 6k +4k). 6 volts.

Relax, feel free to refer back because we will be coming back to these points.

4.   Next, Figure D is a typical gain stage triode circuit, and Figure E is the AC Thevenin Equivalent Circuit of Figure D. No DC voltage is applied. This will be covered later. (Engineering textbook, Semiconductor and Tube Electronics, by James G. Brazee).

5.   In Figure E, X is our AC source, Rp is the tube plate resistance from the specification sheet, and RL is our plate resistor to B+.  (I made up my own tube with specs sheet of Mu = 10, Rp is 4k ohms.)

6.   Figure E, RL is grounded at  point H.

7.   Notice Figure E, we have AC voltage source with Rp in series with RL to ground, just like in Figure C, because it is the same circuit. (The equation again is 10 volts x (RL / RL + Rp), or 10 x (6k/6k + 4K) = 6 volts AC.) All this can be easily measured to verify in our basic tube circuit.

8.   Our tube circuit will not work without DC voltage applied. But RL at H point to ground would short out the DC power supply.

9.   So letís add the DC battery voltage to our Thevenin Equivalent Circuit Figure E? The result is Thevenin Equivalent Circuit Figure F, which deals with both AC and DC voltages.

10.   What is the difference between Figure E and F? One difference is power supply filter capacitor C1 is added so our B+ does not short to ground.

11.   Secondly, RL is not directly connected to ground anymore at H, but through C1 to ground.

12.   So we have a voltage divider, like Figure C, but with an additional part, C1. So we have our AC source, Rp, RL, and C1.

13.   Now, we need to understand that C1 has AC resistance (Xc). (Actually reactance but letís keep it simple with no phase angles.)

14.   So now the AC output voltage = 10 x (RL + Xc / RL + Xc + Rp

15.   But what value is the AC resistance (Xc)? That depends upon the frequency.

16.   (The AC resistance (Xc) is calculated:   1 / 2PI x F x C. That is 1 divided by 6.28 times Frequency in hz times Capacitance in Farads.) As one can see, Xc is frequency dependent.

17.   So in our voltage divider, the output voltage will depend upon the frequency since RL + Xc changes with frequency..

18.   I have thus proven that the output voltage varies with frequency, thus the frequency response is not flat. (Thevenin Equivalent Circuits have been used in engineering circuits for decades and decades.)

The AC source we used can be simply musical voltage.

19.   Figure K is what you would see as the actual schematic circuit that we discussed.

20.   If we calculate or measure the AC musical signal current through C1, it will be at least 15 times the musical signal current through the coupling capacitor/Rg combination. I am lenient due to Y (a resistor or choke) siphoning off some AC musical current.

21.   We can calculate or measure the AC voltage at C1 but we need to know the frequency. At 20hz, a 20uf capacitor has 400 ohms Xc. The equation is: 6 AC volts x (Xc \ Xc + RL) The answer is approximately 0,2 volts AC. The C1 AC voltage will vary with circuit gain, C1ís value, Rp, RL, AC frequency.

Not only is the white paper correct, but goes further, because capacitors have ESR, internal inductance, and self resonance problems. Even very small capacitors have problems since tonal balance is so easily perceived.

See Walter Jung and Richard Marsh have an article ďpicking capacitorsĒ that includes measurements, resonance problems, ESR, DA etc.

https://www.yumpu.com/xx/document/view/23313452/picking-capacitors-part-1-walt-jung
http://www.reliablecapacitors.com/pickcap.htm

Cheers

Steve





« Last Edit: September 10, 2018, 09:27:42 PM by steve »
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Offline steve

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Re: How important is Power Supply Design?
« Reply #34 on: September 12, 2018, 05:12:14 PM »
Here is an abbreviated version, just a couple of points for those who feel overwhelmed by my above post, yet wants to see some proof that the power supply capacitor does handle musical signal current, has voltage across it, as well as causes non linear frequency response by its changing AC resistance vs frequency.



The top diagram is a typical schematic circuit and lower diagram is the Thevenin Equivalent Circuit of the top diagram, including both AC and DC voltages.

We just have a simple series voltage divider consisting of Rp (tube plate resistance), RL resistor, and power supply capacitor C1's AC resistance/Xc (varies with frequency). The equation is Xc = 1 / 6.28 x F x C.    Xc = 1 / 6.28 x Frequency HZ x Capacitor's value.

Proof that the frequency response varies with frequency due to power supply capacitor C1.

Cheers

steve
« Last Edit: September 12, 2018, 05:13:57 PM by steve »
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Offline Nick B

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Re: How important is Power Supply Design?
« Reply #35 on: September 13, 2018, 03:36:13 PM »
Ok, it was good and quite informative while it lasted. Iím not able to make any judgments on whoís right or wrong as the technical discussion is way above me. What I do know is that Steve is an accomplished designer and Folsom makes great sounding products according to Dave, whose ears I trust and whose Uber I love. And then thereís Gary who loves diy and whose cables I use and they sound really good. So my final words are ďpacem in terris ď or Iíll lock the thread

Steve,
Thanks for the simplification. You may be be teaching at a 3rd grade level, for example, but I feel like Iím still in preschool. I am trying to remember what C1 means when I reread your post.....Not all is lost however, for I do know the difference between AC and DC....Tesla vs Edison. And I always opt for the upgraded/best power supply when available. Please continue with your posts as I continue to play catch up via various means
Nick
« Last Edit: September 14, 2018, 09:52:24 AM by Nick B »
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Offline steve

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Re: How important is Power Supply Design?
« Reply #36 on: September 13, 2018, 08:28:32 PM »
Ok, it was good and quite informative while it lasted. Iím not able to make any judgments on whoís right or wrong as the technical discussion is way above me. What I do know is that Steve is an accomplished designer and Folsom makes great sounding products according to Dave, whose ears I trust and whose Uber I love. And then thereís Gary who loves diy and whose cables I use and they sound really good. So my final words are ďpacem in terris ď or Iíll lock the thread

Steve,
Thanks for the simplification. You may be be teaching at a 3rd grade level, for example, but I feel like Iím still in preschool. I am trying to remember what C1 means when I reread your post.....Not all is lost however, for I do know the difference between AC and DC....Tesla vs Edison. And I always opt for the upgraded/best power supply when available. Please continue with your posts as I continue to plat catch up via various means
Nick

Your welcome Nick. I try not to teach down, but I don't know the general public's level, I don't wish to insult anyone, but I also want all to understand if possible. Knowledge is power.

C1 is a power supply "decoupling" capacitor. Capacitor C1 will tend to pass an AC signal while preventing the DC voltage from shorting to ground. Passes AC while blocking DC is a nice way of putting it.
We will call AC resistance (Xc).

A capacitor blocks DC but tends to pass AC.

A resistor provides resistance to both AC and DC.

A choke tends to block AC but tends to pass DC.

General statements but pretty good at helping us to understand our basic circuit.

A resistor's resistance value is simply what is stated on the resistor, for either AC or DC.

For any capacitor, the DC resistance is approximately infinite. Makes sense since a capacitor blocks DC.


For a capacitor, the AC resistance (Xc) = 1 / 6.28 x Frequency in hz x Capacitance in farads (ufd is millionths of a farad).

For 10 ufd capacitor:

Xc = 1 / 6.28 times 20hz times 0,00001 farads = 796.178 ohms AC resistance.

At 200 hz, Xc = 1 / 6.28 x 200hz x 0,00001 farads = 79.6178 ohms AC resistance.

At 5k hz, Xc = 1 / 6.28 x 5000hz x 0,00001 farads = 3.184 ohms AC resistance.

If any questions so far, please feel free to ask.

Cheers

steve

         
« Last Edit: September 13, 2018, 08:37:42 PM by steve »
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Offline steve

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Re: How important is Power Supply Design?
« Reply #37 on: October 21, 2018, 08:09:41 PM »
Ok, we learned that Xc1's AC resistance (Xc1) varies with frequency.

By definition, we know that Rp's DC and AC resistances are the same at audio midband. By defintion, we also know RL's DC and AC resistances are the same at audio midband.

Checking reply #34, we see that Rp is in series with RL is in series with Xc1 to ground. Since Xc1 varies with frequency in the audio band, Rp + RL + Xc1 varies with frequency.

Since Rp + RL + Xc1 varies with frequency, the gain is also going to change vs frequency.

Since the gain changes vs frequency, the output signal voltage will vary with frequency.

I hope this helps one to understand how the power supply capacitor is not only in the musical signal path, but also alters the gain vs frequency. If you have a question, or don't understand something, please ask.

cheers

steve
« Last Edit: October 21, 2018, 08:40:28 PM by steve »
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Offline steve

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Re: How important is Power Supply Design?
« Reply #38 on: October 27, 2018, 11:20:25 PM »
    Yes known laws dictate the basics, but but sometimes different approaches within the laws render different outcome.
   We cannot become so ruled by law that we cannot imagine. We would not go forward if we did. All I know changing a cap in the power supply gives me a different sound.

charles

I have decided to respond to your post Charles. One cannot sometimes use different approaches within the laws as the laws are the laws. E = I x R does not change because one wants it to. The same with Kirchoff's and Norton's laws.

One cannot say only some musical signal current, or no signal current flows through the power supply filter capacitor because we don't like it, as Folsom claims. 

Out of all the comments Folsom posted, his clearest stated position, which I will address is:

Folsom:
Quote
I'm not going to go in circles talking about power supply caps that magically become signal capacitors...

And I'm not going to work against all the absurd assertions.

That comment is complete nonsense, a capacitor does not create its own signal.

Secondly, a power supply decoupling capacitor has signal current flow as I have clearly proven in posts #19 and #33, so  calling this aspect "absurd" is also complete nonsense.

Thirdly, we cannot claim the power supply decoupling capacitor impedance (Z) is irrelevant and doesn't make any sonic difference because we don't like it. Why?

Changing filter capacitors and perceiving different sonics will occur due to different ufd, ESR, DA, resonance, physical construction, materials, and termination techniques. All these different characteristics will affect how the musical signal current flows through the power supply decoupling filter capacitor. Laws are laws.

========

In general, I was initially hoping we could have a nice discussion and learn how a circuit actually works, and in more depth than typical explanations. I am certainly glad two EEs chimed in to support me, as well as my engineering textbooks, RCA Radiotron Designers Handbook, with 26+ electrical engineers, as well my electronics engineering classes.

But it appears the string has been damaged to such an extent, by two, that no one wishes to participate. Maybe next time.

cheers

steve
« Last Edit: October 27, 2018, 11:45:46 PM by steve »
Steve Sammet (retired, owner, SAS Audio Labs)
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Offline steve

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Re: How important is Power Supply Design?
« Reply #39 on: July 30, 2019, 08:13:22 PM »
I have discontinued my website, at least for now, so all my white papers are not available. However,
the premise that musical signal current flows through the power supply decoupling capacitor is
scientifically correct.

For ease, I have again drawn out a simple/typical two stage circuit one would see in a schematic,
bottom of this post. Figure 1 is a typical gain stage driving the following stage.
 
Point A is a musical signal output point, with ground as reference. (We typically measure both
DC and AC signal voltages to ground.)

Notice the 2 red lines, which show the AC musical signal current paths from point A to ground.
Notice each red line has only one capacitor and one resistor.

One signal current path is from point A through C1 and Rg1 to ground.
The second musical signal current path is from point A through RL and C (the decoupling capacitor)
to ground.

Figure 2 should be easier to understand as I left out the non essentials for our purposes. We only
need to inspect point A and the two red lines to ground.

Again, one musical signal current path is from point A through C1 and Rg1 to ground.
The second musical signal path is from point A through RL and C (the decoupling capacitor) to
ground. That decoupling capacitor is the last power supply filtering stage.

If we placed an AC current meter, we would measure musical signal current flowing through
each red line. (As a side note, the power supply decoupling capacitor is in the signal path since
it handles some musical signal current.)

----------

As bonus information, RL's resistance value is generally smaller than Rg1's resistance (sometimes much
smaller), so more musical signal current actually flows through the decoupling capacitor C, than
through the coupling capacitor C1.

So C decoupling capacitor quality is even more important than the quality of C1 capacitor.

Knowing true scientific knowledge leads to better understanding of how a circuit works, and what is
important in designing.

Cheers
steve
« Last Edit: July 30, 2019, 09:34:28 PM by steve »
Steve Sammet (retired, owner, SAS Audio Labs)
"V" Very Low Capacitance Interconnects
SAS Audio Labs Test Phono Stage
SAS Audio 11A Tube Reference Preamplifier
SAS Audio Labs 25 W Triode Reference Monoblocks
2 way test Spkrs, 28 - 20khz  -3db (28hz)

Offline rollo

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Re: How important is Power Supply Design?
« Reply #40 on: August 01, 2019, 05:39:07 AM »
  Thanks Steve for the input and hard work. No EE here just Ears. My ears tell me that a properly designed power supply when compared to another it sounds better.
 Yes Caps in PS will sound different. Dave Slagle made several dry chokes one day to compare to a NOS oil filled cap in a power supply. Slagle apologized to all present after he HEARD the difference. He stated" In all my Engineering years I would never suggest a difference in sound" . BTW it was at Mike Matteras home.

charles
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Offline steve

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Re: How important is Power Supply Design?
« Reply #41 on: August 01, 2019, 04:43:50 PM »
  Thanks Steve for the input and hard work. No EE here just Ears. My ears tell me that a properly designed power supply when compared to another it sounds better.

charles

I don't know who those individuals are, and I believe you did not mean "choke" when comparing capacitors.
I will just work with your initial comments, which are quite true from my testing and others.

Anyway.

I have seen many many coupling capacitor exchange strings. There is no doubt that different
brand, types, of coupling capacitors influence the sonics.

Yet I notice there are very few strings concerning power supply decoupling capacitors, which almost
always handle more musical signal current than coupling capacitors, and influence the sound so
profoundly.

For general consumption based upon my previous post #39 schematic, and bottom of this post.

Let me do an example. Let's say we have 20 volts rms at point A in my previous post schematic.
Coupling capacitor C1 is a generous 1ufd. At 1 khz the capacitive reactance (Xc) is 160 ohms.
Rg1 is 100k ohms.
Total reactance is 100,160 ohms.
Current flow through C1/Rg1 is 20 volts rms divided by 100,160 ohms at 1khz. We have
0,00019968 amps of current. That is 0,19968 ma. (0,19968 milliameters of current through both C and Rg1
at 1khz, midband.

Ok, so let's say we run a 12AX7 triode tube, and C is 20ufd, still 20 vrms.
RL is 60,000 ohms.
At 1khz, C reactance is 8 ohms.
Total reactance is 60,008 ohms.
C/RL current flow is 20 volts rms divided by 60,008 ohms at 1khz. We have 0,33328 ma of musical signal
current flow.

1. Signal current flow through C capacitor is 1.669 times higher than signal current flow through C1.
With a different tube, RL values, musical signal current could easily be a factor of 10 or 20 higher than
with a 12AX7 tube. Higher signal current means higher quality decoupling capacitor C.

2. The power supply decoupling capacitor C is usually many many times larger in value to C1 as well,
thus even more important to get the quality of C decoupling capacitor as high as possible.

Cheers
steve

 
« Last Edit: August 01, 2019, 05:08:46 PM by steve »
Steve Sammet (retired, owner, SAS Audio Labs)
"V" Very Low Capacitance Interconnects
SAS Audio Labs Test Phono Stage
SAS Audio 11A Tube Reference Preamplifier
SAS Audio Labs 25 W Triode Reference Monoblocks
2 way test Spkrs, 28 - 20khz  -3db (28hz)

Offline rollo

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Re: How important is Power Supply Design?
« Reply #42 on: August 02, 2019, 07:35:31 AM »
  Yes a choke. Dave Slagle is known for his autoformers and custom, transformers, speakers and Strain Gauge cartridge.. Cannot remember name of his company. He makes exotic stuff that just sounds wonderful.


charles
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Offline steve

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Re: How important is Power Supply Design?
« Reply #43 on: August 02, 2019, 09:17:00 AM »
  Yes a choke. Dave Slagle is known for his autoformers and custom, transformers, speakers and Strain Gauge cartridge.. Cannot remember name of his company. He makes exotic stuff that just sounds wonderful.

charles

Hi Charles,

Ah strain gauge cartridge, now I remember Dave. Either way, I am glad to have Dave on board.

Cheers and thanks.
steve
« Last Edit: August 02, 2019, 04:12:34 PM by steve »
Steve Sammet (retired, owner, SAS Audio Labs)
"V" Very Low Capacitance Interconnects
SAS Audio Labs Test Phono Stage
SAS Audio 11A Tube Reference Preamplifier
SAS Audio Labs 25 W Triode Reference Monoblocks
2 way test Spkrs, 28 - 20khz  -3db (28hz)