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Old 30th May 2012, 03:58 PM   #481
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Quote:
Originally Posted by AndrewT View Post
Simply adding in a parallel diode to the source resistor is not advised.

I have asked a few times what is the set up procedure to give the diode version of the F5 a real chance to perform well. To date I seem to be the only one answering myself.

I still have to write up partIII.
I am quite sure Patrick has the intelligence on how to properly bias up the circuit with diode in place.

Hopefully other people would also realise to adjust trimpots back to zero before turning on and slowly rebiasing the circuit.
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Old 30th May 2012, 04:07 PM   #482
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Andrew,
Do you believe that the diode does indeed contribute to a higher Class potentital than what is set at stand still?
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Old 30th May 2012, 04:09 PM   #483
EUVL is offline EUVL  Europe
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> it is very quick and easy to wire a diode into your circuit.

How do you now I have not tried ?



Have you tried what I proposed ?


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Old 30th May 2012, 04:18 PM   #484
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by buzzforb View Post
........Do you believe that the diode does indeed contribute to a higher Class potential than what is set at stand still?
no.
I think the ClassA output remains the same.
I think that the amp needs the biasing to be redesigned such that the diodes do not pass during the quiescent condition.
I believe that if the diodes start passing during the periods that output current is between Ibias current value and two times Ibias current value, that this will introduce distortions that are avoided by ordinary ClassA operation.
I believe the diodes should only pass when the output current exceeds the maximum ClassA current.
I think that ClassA operation will be compromised if the "diodes turn on" while the output current is still in the ClassA region.

I have no idea what that "diode turn on" current level ref. maximum ClassA current should be. Could it be @ 0.9*Ibias, or 1.7*Ibias, or 2.5*Ibias?

It is because of all these imagined concerns and my lack of knowledge that I keep asking the same question.
Quote:
adjust trimpots back to zero before turning on and slowly rebiasing the circuit
This implies that the diodes have already turned on at the normally recommended Ibias level of ~600mA, ie. zero output current level. Otherwise there would be no need to turn down the bias adjusters.
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Last edited by AndrewT; 30th May 2012 at 04:29 PM.
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Old 30th May 2012, 04:20 PM   #485
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I have not tried anything as yet. I just got back into this after over a 1 year break.
It is easy enough for me to try for myself. I will do it eventually.
Just want to finish my speakers first.
I have too many ideas and if I don't focus on one of them I won't get anything done.
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Old 30th May 2012, 04:24 PM   #486
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Originally Posted by AndrewT View Post
It is because of all these imagined concerns and my lack of knowledge that I keep asking the same question.
this implies that the diodes have already turned on at the Ibias level, ie. zero output current level.
There are so many variables Andrew, the only way is to just try for yourself.
You guys really know how to get me off track.
If you guys want me to do it in the lab I will do it with real performance measurements.
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Old 30th May 2012, 04:55 PM   #487
EUVL is offline EUVL  Europe
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Andrew,

Perhaps worth revisiting posts #71, 72, 129, 132, 173 ?


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Old 30th May 2012, 05:18 PM   #488
AndrewT is offline AndrewT  Scotland
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You're just proving how bad my memory is.

I don't recall any of those 5 posts.

February ! I was in Morocco. Did you lot explore this without my permission?

Can't be that, I posted on 10th and 17th Feb.
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Last edited by AndrewT; 30th May 2012 at 05:21 PM.
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Old 30th May 2012, 06:20 PM   #489
EUVL is offline EUVL  Europe
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I guess one can say I have a prejudice against the diode. I do.
But it is not unfounded, as you can see from post #71, 72.

Real measurements ain't too different.


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Last edited by EUVL; 30th May 2012 at 06:23 PM.
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Old 30th May 2012, 06:38 PM   #490
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You guys need to think outside the box.
Instead of thinking I don't like the idea of this. Why not think how can I make this work.
There are already so many other non-linearities without the diodes.
I reckon it is a drop in the ocean.
Nelson is not going to suggest something that will make the amp sound worse.
It's just a puzzle to solve.
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