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Old 30th July 2012, 02:28 PM   #431
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Quote:
Originally Posted by flg View Post
Obviously I don't know the details of the circuit or Xfrmr so I am just guessing too! If all the windings are actually equal (1:1+1) that is a big hint. Is that true? Has NP actually agreed to that. 150 ohm, 600 ohm, or whatever?
Is this mean that 1 Vp-p [for example] across the primary winding generates 1 Vp-p across the upper secondary winding and another 1 Vp-p across the bottom secondary winding? If yes, this hints the voltage gain of the transformer is equal to 2.




Going back to thread #38 and its attendant schematic [and explanation] of the bjt OTL;
  • The suggested interstage transformer is step down [6:1].
  • No specific mention in the text of voltage gain of its output stage. Was it inadvertent?
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Old 30th July 2012, 02:40 PM   #432
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Originally Posted by Antoinel View Post
Is this mean that 1 Vp-p [for example] across the primary winding generates 1 Vp-p across the upper secondary winding and another 1 Vp-p across the bottom secondary winding? If yes, this hints the voltage gain of the transformer is equal to 2.
Yes, that could be said to be true. But, in it's application that may not be correct for the circuit as a whole.
Some baseless assumptions on my part: I would expect gain from the bottom FET.
I would imagine the Xfrmr could be 1:1+1 or possibly a higher turns ratio on the top FET.
I would also expect the circuit to work without FeedBack.
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Old 30th July 2012, 03:26 PM   #433
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Originally Posted by flg View Post
Yes, that could be said to be true. But, in it's application that may not be correct for the circuit as a whole.
Some baseless assumptions on my part: I would expect gain from the bottom FET.
I would imagine the Xfrmr could be 1:1+1 or possibly a higher turns ratio on the top FET.
I would also expect the circuit to work without FeedBack.
All of our threads are food for thought. No harm at all in chewing them over [by inspection] so as to understand how F6 [and other circuits] generally work. Clearly; when Mr. Pass speaks, writes and puts forth a new schematic like F6 and others, everybody listens and reacts to it. 400 + threads! and counting.
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Old 30th July 2012, 04:35 PM   #434
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Quote:
Originally Posted by flg View Post
Obviously I don't know the details of the circuit or Xfrmr so I am just guessing too! If all the windings are actually equal (1:1+1) that is a big hint. Is that true? Has NP actually agreed to that. 150 ohm, 600 ohm, or whatever?
who cares what NP have to tell ?

I only care what Pa is telling



whatever - is it 4x600R or is it 4x150R is just matter of friendly dispute between Pa and moi ;

fact is that 2SK170/2SJ74 buffer is able to drive it , be it 150 or 600 (and it is 150 per section )
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Old 30th July 2012, 04:38 PM   #435
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Originally Posted by lhquam View Post
The Jenson JT-123-FLPCH has inter-winding capacitances of 18nF. When these are taken into account, "pure symmetry" is lost because the secondary for the upper FET is moving with the output signal, vs the secondary of the lower FET is at a nearly constant voltage. The result is that the capacitive coupling to the gates introduces significant 2nd harmonic.

Now I understand why 0.1% THD at 1 watt might be expected, unless there are some tricks to be discovered.
I don't think you do understand. The capacitance of the transformer would
only influence the distortion at higher frequencies, not at lower, but when
we look at the open loop (or closed loop) distortion of the F6 prototype
we don't see an increase in distortion at the frequency extremes.

Remember that the quadfilar windings have symmetric capacitance, so all
windings exhibit the same conditions with respect to that.

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Old 30th July 2012, 04:39 PM   #436
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regarding gain of output stage - purely from lacking of my institutional electronic education , but primarily because of my laziness - lets just say that - I'm not erring more than 3db ...... and - Papa will , eventually, explain everything in article .
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Old 30th July 2012, 04:44 PM   #437
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Originally Posted by Nelson Pass View Post
I don't think .........
also - when we take output impedance of input buffer , reflected to each secondary , we have approximately 70R vs.18nF , in worst case


pretty high (freq) , at least in my book ........ if needing anything - it needs RC across secondary , to tame it
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Last edited by Zen Mod; 30th July 2012 at 04:48 PM.
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Old 30th July 2012, 04:49 PM   #438
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Originally Posted by lhquam View Post
I found a very useful book chapter on audio transformers, by Bill Whitlock of Jensen Transformers. http://www.jensen-transformers.com/a...%20Chapter.pdf
That reminds me. I saw this last night but did not respond cause I went off reading and saving it. great find lhquam
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Old 30th July 2012, 04:53 PM   #439
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Originally Posted by Zen Mod View Post
also - when we take output impedance of input buffer , reflected to each secondary , we have approximately 70R vs.18nF , in worst case

pretty high (freq) , at least in my book ........ if needing anything - it needs RC across secondary , to tame it
Isn't that more like 30-40R? Rsource * (Turns ratio) ^2 ???
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Old 30th July 2012, 04:58 PM   #440
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nope

((1/S+Rs) // (1S+Rs)) x 2 , where x2 means divided to 2 secondaries , meaning that each secondary will have half of current capability of source
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