F5 power amplifier - Page 1118

AndrewT · 06:47 PM

VA = Vac * Iac when driving a resistor to maximum power rating.

When you attach a capacitor input filter, the manufacturer tells us that you must apply a de-rating factor. Somewhere around 0.7 for DF is about the usual. This takes account of the extra heating effect of I^2 R when the current is not sinusoidal nor smooth DC.
The crest factor ofr peak current to average current is at least 5 and possibly as high as 20, when very good capacitors are used for smoothing.

The total maximum continuous output power of the transformer must be ~70% of the VA rating when feeding a capacitor input filter.

Rectify and smooth the output from your transformer.
The maximum continuous DC current must be ~ 50% of the Iac rating.
The total maximum power drawn from the transformer is ~0.7 * Vac * Iac = Vdc * Idc
re-arrange the equation to find maximum continuous DC output current and you get:
Idc = 0.7 * Vac * Iac / Vdc = 0.7 * Vac * Iac / sqrt920 / Vac (using Vac here takes account of the power absorbed by the rectifier. ClassA bridge rectifier need to be cooled).
Idc max = 0.7/sqrt(2) * Iac ~= 50% of Iac rating.

BTW,
I have an almost identical 225VA (25+25Vac) RS transformer. I use it to power a chipamp.

carlomar · 20th November 2011, 07:35 PM

Tanks AndrewT,

I have to read more about Class A power Supply.

One thing is certain, since i have no problems with just one 225VA:

With two transformers 225VA, one per channel one, I can consider the power supply well calculated.

Nelson Pass · 20th November 2011, 10:05 PM

The F5 continues to be more popular than I expected. As a reward to the
faithful, I have completed the F5 Turbo.

The pc boards are on order, and when they arrive I will present it complete.

ps - you can modify existing F5's to make one.

sekess · 20th November 2011, 10:10 PM

Outstanding - can't wait

Steve

6L6 · 20th November 2011, 10:22 PM

Yippie!!!!!!

njepitt · 20th November 2011, 10:25 PM

Oh wow.... I've been planning and collecting parts for a rebuild of my F5 - can't wait to hear more about a turbo-ed version...

jackinnj · 20th November 2011, 10:28 PM

Quote:

Originally Posted by Nelson Pass

The F5 continues to be more popular than I expected.

The design of the F5 is elegant, the parts count is low, and the performance is superb...why would you have expected anything less?

Russellc · 20th November 2011, 11:14 PM

Perfect....Just began another F-5, but think I will wait for this one!

Russellc

TheAnaesthetist · 20th November 2011, 11:28 PM

Me too. Interesting...

Zen Mod · 20th November 2011, 11:52 PM

lemme guess ........ less OLG ........ less feedback ...... or feedback-less ?

20th November 2011, 06:42 PM	#11171
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	VA = Vac * Iac when driving a resistor to maximum power rating. When you attach a capacitor input filter, the manufacturer tells us that you must apply a de-rating factor. Somewhere around 0.7 for DF is about the usual. This takes account of the extra heating effect of I^2 R when the current is not sinusoidal nor smooth DC. The crest factor ofr peak current to average current is at least 5 and possibly as high as 20, when very good capacitors are used for smoothing. The total maximum continuous output power of the transformer must be ~70% of the VA rating when feeding a capacitor input filter. Rectify and smooth the output from your transformer. The maximum continuous DC current must be ~ 50% of the Iac rating. The total maximum power drawn from the transformer is ~0.7 * Vac * Iac = Vdc * Idc re-arrange the equation to find maximum continuous DC output current and you get: Idc = 0.7 * Vac * Iac / Vdc = 0.7 * Vac * Iac / sqrt920 / Vac (using Vac here takes account of the power absorbed by the rectifier. ClassA bridge rectifier need to be cooled). Idc max = 0.7/sqrt(2) * Iac ~= 50% of Iac rating. BTW, I have an almost identical 225VA (25+25Vac) RS transformer. I use it to power a chipamp. __________________ regards Andrew T. Last edited by AndrewT; 20th November 2011 at 06:47 PM.

20th November 2011, 10:10 PM	#11174
sekess diyAudio Member Join Date: Feb 2006 Location: NJ	Turbo Outstanding - can't wait Steve

20th November 2011, 10:22 PM	#11175
6L6 diyAudio Member Join Date: Oct 2010 Location: Denver, Colorado	Yippie!!!!!! __________________ Pass Labs Pearl Phono -- Pass B1 Preamp -- Pass F5 amplifier -- Pass Labs Pearl 2

20th November 2011, 10:25 PM	#11176
njepitt diyAudio Member Join Date: Aug 2008 Location: Brasilia	Turbo!?! Oh wow.... I've been planning and collecting parts for a rebuild of my F5 - can't wait to hear more about a turbo-ed version...

20th November 2011, 11:28 PM	#11179
TheAnaesthetist diyAudio Member Join Date: Oct 2009 Location: Maastricht	Me too. Interesting... __________________ DCB1, F5, Troels Gravesen DTQWT


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20th November 2011, 07:35 PM	#11172
carlomar diyAudio Member Join Date: Dec 2004 Location: lisbon	Tanks AndrewT, I have to read more about Class A power Supply. One thing is certain, since i have no problems with just one 225VA: With two transformers 225VA, one per channel one, I can consider the power supply well calculated.

20th November 2011, 10:05 PM	#11173
Nelson Pass The one and only Join Date: Mar 2001	The F5 continues to be more popular than I expected. As a reward to the faithful, I have completed the F5 Turbo. The pc boards are on order, and when they arrive I will present it complete. ps - you can modify existing F5's to make one.

20th November 2011, 11:14 PM	#11178
Russellc diyAudio Member Join Date: Mar 2003 Location: midwest	Perfect....Just began another F-5, but think I will wait for this one! Russellc

20th November 2011, 11:52 PM	#11180
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	lemme guess ........ less OLG ........ less feedback ...... or feedback-less ? __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; BAF Forum & Gallery;I'm dumb

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