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Old 21st December 2012, 01:26 PM   #701
Marra is offline Marra  United Kingdom
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Thanks Buzz.Would there be any benefit to cascoding or is it a waste of components at +- 35v dc?
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Old 21st December 2012, 01:30 PM   #702
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Cascade keeps Jfet drain at ideal V, reduces mr miller, as well as dissipation. In theory, it should always be better. OTOH, it adds another junction. At35v, all that is moot, as I think it is necessary, because you are really pushing dissipation maximums.
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Old 21st December 2012, 01:44 PM   #703
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try your calculation on the F5 and see if you get 64W dissipation pr ch. (thats the correct number for a F5) and the F5 run on a single 300VA transformer.


Quote:
Originally Posted by BigE View Post
AudioSan,

From the F5 manual:

"For this sort of circuit, a 1.3 amp bias means that the amplifier will operate Class A to 2.6 amps of output current. To understand this, imagine a condition where Q3 and Q4 are
idling at 1.3 amps, so that all the current is going from the V+ voltage rail to the V- voltage rail, and none is going through the loudspeaker."

I read that as 2.6 amps (the total bias through all devices) from V+ to V-. That's also the calculation in AndrewT's post.

Are we both incorrect? The numbers agree perfectly with transformer VA = 6-10 Wrms -- actually perfect at 8 x Wrms.


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Old 21st December 2012, 01:59 PM   #704
BigE is offline BigE  Canada
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I will try them tonight, and repost all the formulas I used -- it looks like I have an error in one -- the number in the post does not agree witht the formula for VAbias.
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Old 21st December 2012, 02:10 PM   #705
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you will get about 124.8W dissipation pr ch with your calculation. twice the acctual numbers.
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Old 21st December 2012, 04:09 PM   #706
Marra is offline Marra  United Kingdom
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Quote:
Originally Posted by buzzforb View Post
Cascade keeps Jfet drain at ideal V, reduces mr miller, as well as dissipation. In theory, it should always be better. OTOH, it adds another junction. At35v, all that is moot, as I think it is necessary, because you are really pushing dissipation maximums.
Thanks for confirming what I was thinking.Do I stick with two pairs of outputs and bias high or try four and bias lower.I guess its try both and see which I prefer.
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Old 21st December 2012, 04:19 PM   #707
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keep bias at around 0.9A pr device. over that and you risk that diodes starts cunducting within bias. if you want higher bias, then you can add more outputs or lower the source resistor values.
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Old 21st December 2012, 04:35 PM   #708
a.wayne is offline a.wayne  United States
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When Buzz finishes his 8pr version , we will be shown the way ...
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Old 21st December 2012, 04:40 PM   #709
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8 pair? that is just insane i hope there is dual input pairs too
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Old 21st December 2012, 06:15 PM   #710
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Quote:
Originally Posted by a.wayne View Post
When Buzz finishes his 8pr version , we will be shown the way ...
Ha! Actually ave a decent excuse today. In NewJersey.
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