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Enochrome
diyAudio Member

Join Date: Nov 2011
Quote:
 Originally Posted by PRR > how does one determine the output power of the Mofo? Pout = ((VDC*0.64)^2)/RL ("0.64" is 0.707 for peak-to-RMS, and 0.9 for general loss.) IDC = VDC/RL (This could perhaps be 0.9VDC but a hair-rich beats any-cold.) Total DC power = 2.5 times output power Power making heat in heatsink = also 2.5 times Pout (Drops to 1.5X when working FULL Sine power, but you only do that on test-bench.)

Thanks for the quick and detailed response. Most of that was beyond my comprehension, so in that I might have to focus on one of the first watt amps.

Is there a thread in the Pass Labs or DIY Audio site that is dedicated to people just starting out in electronics? If not, I think that it could possibly be a good idea.

Thanks again. I do appreciate it.

 8th November 2018, 11:26 PM #1542 Zen Mod   Official Court Jester diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain First Watt site - articles __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
 9th November 2018, 01:06 AM #1543 PRR   diyAudio Member     Join Date: Jun 2003 Location: Maine USA >> Pout = ((VDC*0.64)^2)/RL > ....that was beyond my comprehension... Math. To estimate power output: Determine your supply voltage. Call it "VDC". Multiply VDC by 0.64. (Don't ask why, yet.) Find the Square of that number. (Multiply it by itself.) Divide that number by the load resistance "RL". For 19V supply and 8 Ohm load: 19V times 0.64 makes 12.16. 12.16 times 12.16 makes 148. 148 divided by 8 Ohms makes 18 Watts. However you want to work through the other calculations. The 19 Volt supply MUST have relatively BIG current; not some old answering-machine wart. The heatsink for a larger MoFo needs to be quite large.
 9th November 2018, 02:38 AM #1544 e_fortier   diyAudio Member     Join Date: May 2001 Location: Eastern Canada Is the Output power really 18W with a 19Vdc supply ? I thought the designer mentioned 12W. Mind you, I haven’t measured mine and 12W vs 18W is probably hard to differentiate by ears. Tomorrow I’m helping a friend building his 2 regular MoFo. BR Eric
 9th November 2018, 12:51 PM #1545 Michael Rothacher   AudioMaker.Tech diyAudio Member     Join Date: May 2001 When I quote power, I'm usually talking about how much you'll get with less than 1 or 2% THD. If you have a look at the THD vs. Power graph from the article, you can see that it makes it to about 18W with around 10% THD. __________________ Visit AudioMaker.Tech
 10th November 2018, 12:32 PM #1546 Dirk1   diyAudio Member   Join Date: Feb 2013 Location: Kassel I can operate the MoFO with two boards as balance amplifier. I currently operate the L`Amp 193V and wanted to use of this then the power supply. If that works I need only a second 193V, another transformer and the other Mofo parts is that correct. kann ich den MoFO mit zwei Platinen als Balance Verstärker betreiben. Ich betreibe zur Zeit die L`Amp 193V und wollte von diesem dann das Netzteil nutzen. Wenn das funktioniert brauche ich nur noch einen zweiten 193V, einen anderen Trafo und die anderen Mofo Teile ist das richtig.
Eric
diyAudio Member

Join Date: Nov 2000
Location: Central PA, USA
Got my MoFo amp finished over the weekend, though I haven't yet had the opportunity to listen to it.

I made it "bread board" style with short legs and ran all of the wires below deck. I made a small, wooden T-support that goes under the base of the sink to improve the airflow a bit and the last few vanes dangle over the edge of the board.

Since the sinks are isolated from one another, the mosfets are mounted with only thermal paste. This allowed me to bump the bias up to 3A for each channel and still limit thermal rise of the sinks to 25c. Using a Dell power brick rated for 12A delivers 19.1v when both channels are driven. The chokes exhibit a thermal rise of about 9c with 3A of current through them.

Can't wait to hear it tonight! It's rather heavy with all of that metal on top!
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My DIY Basement Theater, Aleph-X Amps, Avro Open Baffle Speakers, LDR based BA-3 pre, Pearl II, highly modded Technics SL-1200, F4, M2, Aleph-J, MoFo, a40, several ACAs, FHXL, Tang Band 1772 bass-reflex

Last edited by Eric; 12th November 2018 at 08:27 PM.

 12th November 2018, 08:30 PM #1548 Michael Rothacher   AudioMaker.Tech diyAudio Member     Join Date: May 2001 Wow, that's very spiffy. __________________ Visit AudioMaker.Tech
 12th November 2018, 08:47 PM #1549 Dennis Hui   Hoopy Frood diyAudio Member   Join Date: Aug 2002 Location: Toronto, Canada Beautiful work, Eric! __________________ We are fearless amplifier builders. A little heat doesn't scare us at all. - NP 2002
 12th November 2018, 09:23 PM #1550 El Reino diyAudio Member   Join Date: Oct 2017 Beautiful work Eric!

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