SYMEF amplifier
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 16th March 2012, 11:44 PM #371 OnAudio diyAudio Member     Join Date: Oct 2011 Thanks for joining us pinnocchio and mrsavage.
OnAudio
diyAudio Member

Join Date: Oct 2011

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 22nd March 2012, 11:27 PM #373 PauloPT   diyAudio Member   Join Date: Jan 2010 Location: Lisboa, Portugal Nice looking board! __________________ Kind Regards, Paulo.
OnAudio
diyAudio Member

Join Date: Oct 2011
version 2 of the PCBs

There are likely to be two version of boards on offer, heres the other technic
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 SYMEFV2.png (66.6 KB, 527 views)

CBS240
diyAudio Member

Join Date: Aug 2005
Location: K-town
Quote:
 Originally Posted by AndrewT What is the peak instantaneous output voltage? Use the formula: Imax ~ Current Factor * Vpk / Speaker nominal impedance. Current Factor can be around 2 for a mild reactance speaker using music that does not contain very fast starting signals nor very fast stopping signals. Current Factor can be as high as 5 for "normal" reactance speakers when the music does contain very fast starting signals and/or very fast stopping signals. I adopt CF=3 for my designs. Assuming 40Vpk & 8ohm speaker. Imax ~ 15Apk This is a short term current peak that causes no significant heating of the output devices nor of the heatsink above the operating temperatures.
The output stage must be able to reach the estimated Imax with a sufficient amout of current gain. Even though 40V/8R is 5A, the circuit should be able to deliver 15A in short duty. And of course AC gain varies inversely proportional to frequency.
__________________
All the trouble I've ever been in started out as fun......

 24th March 2012, 02:03 PM #376 OnAudio diyAudio Member     Join Date: Oct 2011 Hi CBS240, I take it you will tackle the bigger version . Your contribution will be much appreciated. kind regards, Harrison.
 31st March 2012, 01:02 AM #377 OnAudio diyAudio Member     Join Date: Oct 2011 PCB updates harrisonaudiolabs.com PCBs Joel, Paulo, Raj, Brian, Evette, Mrsavage, Pinnocchio All the best
PauloPT
diyAudio Member

Join Date: Jan 2010
Location: Lisboa, Portugal
Bias

Last couple of days I’ve been experimenting with different bias values. I went from 50mA up to 230mA, that is from 13mV across emitter resistors up to about 50mV. I didn’t go higher because I was afraid to fry the output transistors.

I found that the sweet spot for me is between 100mA and 200mA. Going higher that 200mA actually made the sound worst, less smooth. 50mA (13mV) is way too low and I could perceive distortion. At 100mA (23mV) the sound is much more smooth and “liquid” than at 50mA. Going higher than 100mA the sound increases in smoothness but is not a night and day difference. Somewhere about 150mA seems where going higher I couldn’t perceive any difference, except that higher than 200mA things change again but for worst sound. I have now the SYMEF biased at 150mA (33mV) and I think it will stay this way.

Drownranger, did you try different bias values? What is your perception?

Incidentally, I soldered a Muse KZ capacitor the wrong way and it became very hot and inflate the top. I wanted to see what’s inside so I opened the can. It then vented a vapor smelling like sulfer. I took some pics of what’s inside and here they are:
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__________________
Kind Regards,
Paulo.

 1st April 2012, 02:47 PM #379 AndrewT   diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders For an EF output stage expect 20 to 25mVre through 0r22re. That comes out at ~100mA of bias through each pair. __________________ regards Andrew T.
 1st April 2012, 02:54 PM #380 drowranger diyAudio Member   Join Date: Aug 2009 nope... hi Paulo, I just stayed at 46mv. across two resistor emitter.theres something I read in books about gm doubling.when you try to bias a class b output as same as class a.besides my heatsink could not handle more heat.height is 3.75" which is very small. regards, joel p.s. next time be aware of the polarity and stick to safety region.

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