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 Post subject: Power supply thoughts
PostPosted: Fri Mar 09, 2018 8:50 pm 
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Nakamichel wrote:
...I found a marvelous way against the ripple that I can't tell here.
http://www.canuckaudiomart.com/forum/viewtopic.php?f=9&t=49541&start=75#p789957

After some discussions with my wife and the fact that my monoblock amplifiers won't be part* of my future audio company, I will share some thoughts of my power supplies.
(*unfortunately, the mosfets Alfet are not available anymore)

I really think that the DC which powers any stage is THE main 'ingredient' for audio.
For many (most ?) audio components, the DC is coming from a transformer followed
by some diodes and capacitors and in some case by a voltage regulator and/or stabilizer etc...

Let's see the basics:
this is the sinewave (60hz) provided by the transformer
Attachment:
60-sector.jpg
60-sector.jpg [ 60.47 KiB | Viewed 1755 times ]

now once rectified by diodes or bridge (120hz)
Attachment:
rectified.jpg
rectified.jpg [ 38.26 KiB | Viewed 1755 times ]

now when the capacitors are added
Attachment:
caps.jpg
caps.jpg [ 44.23 KiB | Viewed 1755 times ]

now we can see the result
Attachment:
dc.jpg
dc.jpg [ 44.72 KiB | Viewed 1755 times ]
As you saw, the DC is still far from being flat.
There's ripple. This ripple can be calculated with some formulas. But it's not the point here.

Let's see how it works
Attachment:
charging-time.jpg
charging-time.jpg [ 15.61 KiB | Viewed 1755 times ]
At the green line (in time), the cap's voltage is lower than the voltage of the transformer.
The transformer begins then to charge the capacitor. Once the the voltage of the transformer does reach its highest point (red line), it can not continue to charge the cap.
So, as you can see, the transformer works only a fraction of the time. Less than 1/4 of the time.

Now back to the rectified sinewave
Attachment:
empty-space.jpg
empty-space.jpg [ 51.19 KiB | Viewed 1755 times ]
There's a big part of the time where the transformer doesn't provide energy (all the parts in red). And we all know that a capacitor doesn't create energy, it can just store it.
When a power supply is constantly working such in a class A stage, combination of transfo-diode-cap can not provide constant voltage as high as the peak of the transfo sinewave.
Impossible because the transformer doesn't provide constant voltage. Then, using that combination we are just lying to ourselves. The energy is just not there.

And when the transfo is not working the capacitor has to release its energy. It will then lose its energy, its voltage will drop until the transfo will charge it again. This makes ripple, non-flat DC.
What I found is that we can at least extend the time the transfo is working. Note, I did not invent this. It already exists and it's not a secret.
But it is not very common since it is not efficient at all. With this way, we have to sacrifice some energy in heat. I do believe then that this is why it is not that common.

Let's see how it works.
We saw that the transfo provides its energy only a small part of time because it's an alternative voltage, a sinewave.
It provides energy when the sinewave is almost at max. The trick is to cut that sinewave with a zener diode and + a transistor if more power is required.
Attachment:
rectified+cut.jpg
rectified+cut.jpg [ 35.02 KiB | Viewed 1755 times ]
Now, the transfo works for a much longer time. And the capacitor for much lesser time. The voltage drop will be considerably less.
More you cut the sinewave, more longer the transfo will work and more flat will be the DC.

I did apply this to all my component at home. On my Nakamichi BX-300 and my wife's Audio Research SP-9, I did cut a big big part of the sinewave.
Both now sound extremely better than ever. The improvement is just impressive. No joke.
The advantages are: much much less ripple, the DC is much stronger (massive PSRR improvement).
In fact, everything is better. Everything.

The price to pay for non power hungry components (few watts lost in heat) is nothing compared to the great improvements.

And finally, I also did it for my big monoblock amplifiers. I only cut 1 volt. 40 (more) watts is lost in heat via the lateral double heatsinks on the sides of my amps.
But the difference is just amazing. That volt lost makes my amps to have the grip of a 250 watts amp.
My composite amplifiers (that drive my mosfets) are not powered by a transformer (or battery)... for those wondering.

- Mik

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PostPosted: Sat Mar 10, 2018 3:46 am 
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Cool. An interesting and informative post. I’m no electronics guy, but the graphs certainly help me understand what is being described. I now kinda get why some folks use battery power for low current pieces like phono pre’s and DACs.

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PostPosted: Sat Mar 10, 2018 4:19 am 
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Equipment with a well designed power supply makes redundant any oil squeezed from snakes to build power cords costing more than a good piece of copper wire.

Here is an invaluable tool:

http://www.duncanamps.com/psud2/index.html

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PostPosted: Sat Mar 10, 2018 5:34 am 
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So are the graphs actual or theoretical?

Your method was to use a specific voltage zener as a shunt regulator in parallel to main out voltage?

Don't think I'd be applying this to an amp!

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PostPosted: Sat Mar 10, 2018 6:20 am 
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What a great discussion !

The attachments are straight out a first year Electronics or Electrical theory course, the pics describe power supply operations perfectly. Don't forget Zener and Resistors will introduce heat and inefficiency to the power supply and in a low power application will not matter much but in a 500W amp, it will be very significant! The best way to introduce low ripple and more efficiency is to raise the frequency of the sine wave from 60 Hz. There's a reason why Aircraft use 400 Hz as it's far more efficient and can use smaller (lighter) capacitors making stuff lighter. Most switching power supplies operate on this very premise by shifting the frequency of operation above 20 kHz and making things even more efficient when rectified as the recovery time will be smaller making less ripple, etc. As Mik depicted, when using Full Wave rectification it doubles the frequency of the supply and makes less ripple and is more efficient than a 1/2 wave rectifier. In North America 60 Hz becomes 120 Hz when bridge (or full wave) rectified and it's easier to filter, imagine the 50 Hz ripple in the U.K. and some other countries, nasty!

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PostPosted: Sat Mar 10, 2018 6:32 am 
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But if varying current across the diode how do you accurately calculate the resistance? And why a zener and not a voltage regulator? Better tolerance...

Someone who's read chapter 2 needs to explain.

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PostPosted: Sat Mar 10, 2018 7:09 am 
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Wow - thanks for this info.
You know a person really understands a topic well, when they can explain it in simple terms.
.
When power transistors draw more current from the power supply, the ripple on the DC rails increases.
This means that the signal transistors in 1st and 2nd voltage stage,
are also operating with more ripple.
So the solution is to have 1 power supply for the signal transistors,
and other one for the power transistors.
.
I suspect, the higher the harmonic content in the ripple - the worse the amp sounds.
One solution to removing harmonics content is
running a C - L - C or C -R - C in the filter section of a power supply,
which softens up the edges of the ripple.

.


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PostPosted: Sat Mar 10, 2018 7:26 am 
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Uunderhill wrote:
... is to have 1 power supply for the signal transistors, and other one for the power transistors...

Multiple, Power Supplies are always a good idea -- For 'numerous' reasons.
I also like, the idea of using local, PS 'Decoupling' Capacitors (*Think PP Metallized Film... If at all po$$$$$ible).


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PostPosted: Sat Mar 10, 2018 7:37 am 
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A zener approach will work, but would be limited to low current applications, like pre-amps.

As Blinky suggested, if you're going to go down this particular rabbit hole, then voltage regulation might be a better approach. It's more complicated, but can be scaled to any voltage/current requirements you might have (or can afford!).

Cheers,Dave


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PostPosted: Sat Mar 10, 2018 7:43 am 
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EDIT this post has an error, please refer to this post, sorry.

I'm a bit surprised some of you don't understand this ultra simple principle.
I'll try to explain even more simpler.

There's no convention or physics law or whatever to tell us what to do with our AC.
The ripple we see on the DC, it is there because we put it there.
We just chose to go with the most efficient manner, in sacrifying quality. That's all.

I agree, if we chop the sinewave, we will lose energy and efficiency.
But for low power ? I prefer by far to have a much more flat DC and loose some energy.

Let's see this simple voltage regulator, I guess everyone will agree with it.
It's just an AC rectified followed by a very simple voltage regulator.
Attachment:
supply -1.jpg
supply -1.jpg [ 77.05 KiB | Viewed 1459 times ]


Now look at this one, look closely, what's changed ?
Attachment:
supply -2.jpg
supply -2.jpg [ 79.67 KiB | Viewed 1459 times ]

I just changed the capacitor, now it is at the end, AFTER the regulator.
Look what happens here. It's simple. I don't know how I could be simpler in my examples.

I discover this 40 years ago playing with a breadboard. I had misplaced my capacitor and on my oscilloscope,
the ripple was very tiny. I was wondering what happened. At the time, with different values, my DC was lower
that expected but it was clean, very clean compared to what I saw with previous attempt.

Edit: my example is a bit weird because I should have marked let's say 7 volt instead 14... but I guess you got it.
And yes Uunderhill, you can add the filter you want... but after the regulator, seen ?
Try it on your breadboard and a scope... you will see... lower DC but better.

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Last edited by Nakamichel on Sat Mar 10, 2018 9:06 pm, edited 1 time in total.

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PostPosted: Sat Mar 10, 2018 8:05 am 
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Nakamichel wrote:
... But experience's ended by pay. I found a marvelous way against the ripple that I can't tell here. But for the PSRR, the trick is simple (but costly) and efficient.

If my 'Primary' concern was just PSRR, as was originally stated.
I 'personally', would have 'tried' approaching this differently if at all possible.
(*There of course is always the matter of 'Cost' and Personal preference).
--
Your way, is very efficient and 'inexpensive' however. GOOD Stuff! :D
Thank-you, for sharing it with us Mik. Greatly Appreciated!


Last edited by Takira71A on Sat Mar 10, 2018 8:21 am, edited 1 time in total.

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PostPosted: Sat Mar 10, 2018 8:19 am 
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Takira71A, you have just misunderstood (or I wrongly explained) when I wrote.
Look now what I really meant:
Nakamichel wrote:
But experience's ended by pay. I found a marvelous way against the ripple that I can't tell here. But for the PSRR, the trick is simple (but costly) and efficient.
The transformers need to have ultra low winding's resistance. My amp are 50w class A, 200w lost in heat. A friend of mine said "why the hell you use 3200va, it's not overkill, it's insane."
The red part is what I explained in this very thread. (I decided to tell it,finally)
The blue part explain that to have a better PSRR, we need to lower as much as possible the R (Z) of the transfo's winding.
When I said (in the blue part) "but costly" I was talking about the transfos. There are 4 transfos, that is costly. (but only one would be ok at 800va)
Hope it's clearer to you.

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PostPosted: Sat Mar 10, 2018 8:28 am 
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Nakamichel wrote:
But experience's ended by pay. I found a marvelous way against the ripple that I can't tell here. But for the PSRR, the trick is simple (but costly) and efficient.
The transformers need to have ultra low winding's resistance. My amp are 50w class A, 200w lost in heat. A friend of mine said "why the hell you use 3200va, it's not overkill, it's insane."

Understood in full 110% now (Thank-you for the 'Red' and the 'Blue'). :D
--
Yes, I too favor the use of 'Low-impedance' Power Transformers. This approach definitely costs more $$$...
But, it is worth it (*Jack Elliano of Electra-Print... Brought this to my attention many, years ago).

Thanks for writing!


Last edited by Takira71A on Sat Mar 10, 2018 8:37 am, edited 1 time in total.

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PostPosted: Sat Mar 10, 2018 8:35 am 
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Yes my friend it is a lot better with lower Z.
If I chose to use 4 transfos of 4 windings each, it is because we can't parrallel many diodes.
With 16 windings, I also have 64 diodes... the current passes... trust me :mrgreen:

My amps are really good. I'm not joking.

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PostPosted: Sat Mar 10, 2018 8:44 am 
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You guys are waay above my pay grade...

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