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Old 11th January 2013, 11:53 PM   #1041
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by AudioSan View Post
100W class A at 8ohm is a bias of 2.5A and about +/-45V rails.
45*2.5*2=225W (this is for 1 channel only ofcourse)
dont you divide by 1.3 for RMS .... ? interesting everyone has a different method or answer vs Rail voltage

Last edited by a.wayne; 11th January 2013 at 11:55 PM.
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Old 12th January 2013, 12:00 AM   #1042
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Originally Posted by a.wayne View Post
dont you divide by 1.3 for RMS .... ? interesting everyone has a different method or answer vs Rail voltage
this is calculation for dissipation. rail voltage*bias*2. or rail voltage*2*bias.
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Old 12th January 2013, 12:02 AM   #1043
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Howdy,
I set my V2 up with no sinks on the diodes,and adjusted the bias around and kept some fingers on the diodes,I set them to around 350 and then cranked the volume and that's when they come on ,I didn't let them stay on too long but a small heatsink should work,I think I will use a heatsink long enought for 2 diodes, maybe keep them closer heat tracking wise.
I read papa's article on them he said they work on the peak times of conducting to keep the impeadance low at high current draw ,if I got that right,LOL.
Thanks for the reply Buzz!
Regards,
NS
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Old 12th January 2013, 11:22 AM   #1044
Marra is offline Marra  United Kingdom
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2455R-100-74 - HONEYWELL S&C - THERMAL SWITCH, NC, 70°C, 55°C | Farnell United Kingdom
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Old 12th January 2013, 11:33 AM   #1045
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Quote:
Originally Posted by noSmoking View Post
Howdy,
I set my V2 up with no sinks on the diodes,and adjusted the bias around and kept some fingers on the diodes,I set them to around 350 and then cranked the volume and that's when they come on ,I didn't let them stay on too long but a small heatsink should work,I think I will use a heatsink long enought for 2 diodes, maybe keep them closer heat tracking wise.
I read papa's article on them he said they work on the peak times of conducting to keep the impeadance low at high current draw ,if I got that right,LOL.
Thanks for the reply Buzz!
Regards,
NS
They dont com eon suddenly, as they are sharong current with the resistors that they are in parallele dwith. As the current increases through that junction the Vdrop increases in proportion to the ratio of their resistance to the Rs. I am not sure they ever complete bypass the Rs, as this would cause instability in the output, moat likely leadin gto thermal runway. I woul dimagine, they work to maintain a similar Vdrop across Rs, regardless of current passing through the junction. Imagine Vdrop staying in the .4-.6V range instead of steadily climbing with increased current. This would affect degeneration amount, bias point, and gain, all in one. Sliding bias
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Old 12th January 2013, 01:03 PM   #1046
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Originally Posted by buzzforb View Post
They dont com eon suddenly, as they are sharong current with the resistors that they are in parallele dwith. As the current increases through that junction the Vdrop increases in proportion to the ratio of their resistance to the Rs. I am not sure they ever complete bypass the Rs, as this would cause instability in the output, moat likely leadin gto thermal runway. I woul dimagine, they work to maintain a similar Vdrop across Rs, regardless of current passing through the junction. Imagine Vdrop staying in the .4-.6V range instead of steadily climbing with increased current. This would affect degeneration amount, bias point, and gain, all in one. Sliding bias
Thanks buzz I'll go back and read that article again,
Regards,
NS
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Old 12th January 2013, 05:04 PM   #1047
dazed2 is offline dazed2  Canada
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Quote:
Originally Posted by buzzforb View Post
They dont com eon suddenly, as they are sharong current with the resistors that they are in parallele dwith. As the current increases through that junction the Vdrop increases in proportion to the ratio of their resistance to the Rs. I am not sure they ever complete bypass the Rs, as this would cause instability in the output, moat likely leadin gto thermal runway. I woul dimagine, they work to maintain a similar Vdrop across Rs, regardless of current passing through the junction. Imagine Vdrop staying in the .4-.6V range instead of steadily climbing with increased current. This would affect degeneration amount, bias point, and gain, all in one. Sliding bias

I thought that people were having trouble even having the diodes turning on? ie , the circuit never gets driven hard enough to reach those V and current levels.
In the V3 with 4 pr is it then necessary to put heatsinks on the diodes?
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Old 12th January 2013, 05:10 PM   #1048
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You want some sort of heat dissipation on the diodes no matter what. You have t consider there ability to get rid of heat. With out any thermal coupling. Their internal temp would vary greatly and make for an unstable amp. As a point in fact, in the Paradise bilders thread, there have been people who have been able to affect bias by simply blowing across the boards. Temperature is a major part of any amp build.It is exponentially more important in CLass A. If you want them to cut on, bolt them to the main sink. For most speakers, V3 without diodes may be sufficient, but it nce to have them.
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Old 12th January 2013, 07:16 PM   #1049
a.wayne is offline a.wayne  United States
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Originally Posted by dazed2 View Post
I thought that people were having trouble even having the diodes turning on? ie , the circuit never gets driven hard enough to reach those V and current levels.
In the V3 with 4 pr is it then necessary to put heatsinks on the diodes?
In my case yes, an 8 ohm load ..? i would still sink them , over building is always fun , lets you concentrate on the music...
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Old 13th January 2013, 02:45 AM   #1050
nrg2009 is offline nrg2009  United States
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So maybe it does make sense to mount the diodes on the main sink to warm them up and get them conducting at a lower voltage? It will also eliminate any concern of them overheating (under load).
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