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Old 18th September 2012, 01:08 PM   #1251
Krisfr is offline Krisfr  United States
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Thanks Gootee for the formulas

I will put these into equations for the Android app.

It kinda reminds me of my FORTRAN instructor chiding me for putting the formula for radar slant range distance from target, taking in the consideration, the curvature of the earth in one statement. I keypunched it into 4 punch cards with a single FORTRAN statement. It had 27 closing parenthesizes.

Although these pages of meaningful thought and consensus, seem worth while to making a decision about how much capacitance to put on a amp rail. I can not hardly wait until I can punch in my own criteria and get an answer to my own question. I may be able to make a PC or non smart phone app too.

Thanks for what this all boils down to.
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Old 18th September 2012, 03:25 PM   #1252
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That would be very nice KrisFr, everyone does not have an Andriod but almost everyone has a PC. I don't think many of us are accessing this thread and writing resposes on a smart phone.
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Old 18th September 2012, 04:47 PM   #1253
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I'll try to fit in the whole test today.
won't be today and probably not tomorrow either.
Going back into hospital to sit with my Dad.
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Old 18th September 2012, 04:55 PM   #1254
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Best wishes and hopes Andrew

Sincerely
-Antonio
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Old 18th September 2012, 08:39 PM   #1255
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Same from Italy,
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Old 18th September 2012, 10:36 PM   #1256
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I found if i decoupled the front end from the output stage with a resistor and capacitor I could get away with more ripple.
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Old 19th September 2012, 03:37 AM   #1257
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Andrew,

good man. I'm doing the same with my wife.
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Old 19th September 2012, 05:24 AM   #1258
gootee is offline gootee  United States
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Andrew,

good man. I'm doing the same with my wife.
Terry and Andrew,

Our hearts are with you and your loved ones.

Please try to remember to also take care of yourselves. It's easy to forget to do that and you can't do them much good if you get too burned out.

Tom
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Old 19th September 2012, 07:20 AM   #1259
djk is offline djk
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"I found if i decoupled the front end from the output stage with a resistor and capacitor I could get away with more ripple. "

Try sneaking a diode in there, Hafler did than in many of their designs.

McIntosh used to use CRCRCR sections (like it was in a tube amp) to feed the front end.
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Old 19th September 2012, 07:50 AM   #1260
gootee is offline gootee  United States
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I think you have demonstrated that the 'standard methods' are completely adequate, when used properly i.e. circuit theory actually works OK.


The justification is simple: normal engineering caution, combined with broad electrolytic value tolerances (can be 20%). The calculation gives the minimum. There seems to be no harm in increasing this (within reason) so increase it. There is no point, and possibly some harm, in increasing it too much. Hence double it. x3 or x4 would be just as good, although maybe unnecessary.

The calculations you have done show good agreement with simulations for lower powers. The discrepancy for higher power mainly comes from Vmin being a bit too small. This has little effect at low power (i.e. high ripple voltage) but is critical at high power (low ripple voltage). As you have included the 0.22ohm drop in Vmin (not a good idea, in my opinion) your Vmin should be bigger for greater power. Try repeating your calcs for Vmin=4V instead of 3V.

Including transformer resistance in the calculations gets messy, unless the resistance is sufficiently low that the cap can recharge more or less fully on each mains half-cycle. As I said in an earlier post, this gets worse for really big caps which may be a reason to avoid really big caps.

So we are in a position where we can calculate, with some confidence, the minimum cap value. We can also estimate, roughly, the maximum. Isn't that 'job done'?
Sorry. I cannot agree.

Attached are some plots for comparisons but I will not be able to analyze them until tomorrow or the next day. They include DC, sine, and square wave loads, with 1650 uF and 6650 uF.
Attached Images
File Type: jpg DC_and_Square_100W_1650uF.jpg (191.3 KB, 114 views)
File Type: jpg DC_and_Square_100W_6650uF.jpg (169.3 KB, 112 views)
File Type: jpg Sine_100W_1650uF.jpg (101.4 KB, 110 views)
File Type: jpg DC_50W_1650uF.jpg (82.6 KB, 107 views)
File Type: jpg Sine_100W_6650uF.jpg (91.7 KB, 109 views)
File Type: jpg DC_50W_6650uF.jpg (78.7 KB, 31 views)
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