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Old 14th October 2012, 02:54 AM   #1431
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Quote:
Originally Posted by Tony View Post
while music is made up from sine waves, there is no comparison with static sine waves, feed your speakers even 1 watt of 60 hz sine waves see if you can stand it....
I am talking about continuous sine wave, not the sine wave that has an envelope, attack and decay, something we call musical sounds...
I see it, finally.
Multiple simultaneous sine waves is a lot more demanding on the power supply than one sine wave.
Thanks!
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Old 14th October 2012, 02:58 AM   #1432
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ripple voltage has a lot to do with your load resistance, not just capacitance, they have to be considered together....

this is from the National Semiconductors' AUDIO/RADIO handbook circa 1980, chapter 6....


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1. Good Regulation means wCRl ~ 10
2. Low Ripple may mean wCRl > 40
3. High efficiency may mean wCRl < 0.02
4. Low cost usually means low surge current and small C
5. Good transformer utilization means low VA ratings, best with full-wave bridge FWB circuit, followed by full wave center tap FWCT circuit.
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Old 14th October 2012, 03:02 AM   #1433
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Quote:
Originally Posted by danielwritesbac View Post
I see it, finally.
Multiple simultaneous sine waves is a lot more demanding on the power supply than one sine wave.
Thanks!
it would be interesting to compare actual energy content of music versus static sine waves....

static sine waves are used in analysis for lack of a better alternative....this issue have been discussed at length here many many years ago...

to keep out feet firmly on the ground, it would be best to know the difference, it has an impact(economic) on our choices as well....
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Old 14th October 2012, 03:12 AM   #1434
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Quote:
Originally Posted by CharlieLaub View Post
You have to iterate around a little bit in order to home in on a particular capacitance. This seems backwards to me - I would instead specify the ripple voltage (for instance something on the order of 0.707 volts seems to be what Tom's number give) and then just list whatever capacitance results from that. You won't be using a 1%, 5% or even a 10% tolerance electrolytic anyway in this application... This would allow you to remove the ripple voltage column and just note at the top that all the capacitance numbers stated give a ripple voltage of 0.707 V (for example). I can understand your confusion about this. At this point, I think that should get you started. -Charlie
Am doin it. THANKS!!
Yes, now that you mention it, specify desired ripple target at the start, totally makes sense, being that it IS the quality control dial that will directly affect realism for LTP or noise for singleton. THANKS AGAIN!!!

EDIT!
I'm stuck.
Entering dramatically different transformer VA doesn't change capacitance like indicated in Tom's spreadsheet. I cannot synchronize the data to reflect (per same ripple figure) what happens to required transformer VA if you either remove half of the capacitance or double it.
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Last edited by danielwritesbac; 14th October 2012 at 03:32 AM.
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Old 14th October 2012, 05:17 AM   #1435
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Quote:
Originally Posted by danielwritesbac View Post
Am doin it. THANKS!!
Yes, now that you mention it, specify desired ripple target at the start, totally makes sense, being that it IS the quality control dial that will directly affect realism for LTP or noise for singleton. THANKS AGAIN!!!

EDIT!
I'm stuck.
Entering dramatically different transformer VA doesn't change capacitance like indicated in Tom's spreadsheet. I cannot synchronize the data to reflect (per same ripple figure) what happens to required transformer VA if you either remove half of the capacitance or double it.
Unless the power level is being changed somewhat significantly, changing VA won't change capacitance all that much. That's because power output is tied to RMS current which is tied to ripple voltage and capacitance. I'm not sure what numbers you are running, but for instance let's investigate a 25+25 transformer and fix ripple voltage at 1 V:
Code:
  VA   power  capacitance
300VA   48     36,177
200VA   45     35,173
150VA   43     34,251
100VA   38     32,382
 80VA   34     30,943
 60VA   29     28,560
What is happening is that, as the VA rating falls, the amount of sag increases. The ripple is being caused by the amplifier draining the caps, and I include both the current delivered to the load as output power and the current that is dissipated power (as waste heat) in this calculation. The total current only falls from 6.04 to 4.79 amps when the VA rating is falling from 300VA to 60VA. That ratio of 6.04 to 4.79 is 1.26 times, the same as the ratio 36,177 uF to 28,560 uF. The capacitance is just not going to go down by half if the ripple voltage is fixed at 1 V.

Personally I think that it is more instructive to see what happens when ripple voltage is allowed to vary (increase). As ripple increases, the available power will decrease and so will capacitance. For instance, let's stick with the 150VA 25+25 transformer:
Code:
Vripple power capacitance
   1      43     34,251
   2      40     16,662
   3      37     10,813
   4      34     7,898
   5      32     6,157
There's your big capacitance drop, and subsequent reduction in output power capability. You can look at the table above and read it right to left and see how reducing capacitance increases ripple voltage and decreases the maximum power output.

I seem to be envisioning the problem in a backwards (or reverse) fashion compared to how others are envisioning it. Maybe that is why we are having trouble getting on the same wavelength...

-Charlie
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Old 14th October 2012, 06:15 AM   #1436
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OK, the next revision of my spreadsheet is now available. I've changed some names and titles and improved some of the graphs, but the guts are the same. I've also added a worksheet containing info on the model, its assumptions, and some basic usage instructions.

Get it here:
Power_Supply_capability_calculations_VER2.2.xls

Here is a screen shot of one of the plots:
Click the image to open in full size.


-Charlie
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Old 14th October 2012, 09:22 AM   #1437
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by Tony View Post
I am curious......now that we have a system of estimating transformer power using static sine waves, i wonder what is the correlation with a typical music? since nobody listens to sine waves....
Quote:
Originally Posted by AndrewT View Post
We all listen to sinewaves. Even when simulated squarewaves and sawtooth waves are inserted into digitally created music, these are composed of sinewaves.
Quote:
Originally Posted by Tony View Post
i can assure you i don't, i use sine waves on dummy loads.....i listen to music exclusively....
Quote:
Originally Posted by Tony View Post
while music is made up from sine waves, there is no comparison with static sine waves, feed your speakers even 1 watt of 60 hz sine waves see if you can stand it....

i am talking about continuous sine wave, not the sine wave that has an envelope, attack and decay, something we call musical sounds...
Thanks for confirming that your statement was wrong and that your defense of that wrong statement was also wrong.
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Old 14th October 2012, 09:26 AM   #1438
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Quote:
Originally Posted by Tony
I am curious......now that we have a system of estimating transformer power using static sine waves, i wonder what is the correlation with a typical music? since nobody listens to sine waves....
just answer the question if you know the answer....
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Old 14th October 2012, 10:09 AM   #1439
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Guys, stick to the technical arguments.
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Old 14th October 2012, 12:00 PM   #1440
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Quote:
Originally Posted by danielwritesbac
Multiple simultaneous sine waves is a lot more demanding on the power supply than one sine wave.
Yes, provided that the frequency, amplitude and phase of these sine waves are such that they add up to some approximation to a low frequency square wave. I thought we established much earlier in the thread that an LF square wave is the hardest thing for a PSU to cope with, in terms of current delivery and hence required reservoir capacitor value. Anything else is easier.

There may be a separate issue with things like IM caused by capacitor nonlinearity, but that is for another thread.
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