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Old 25th May 2012, 03:20 PM   #471
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I have matched jfet models

Mine was biased to 1.3A in both cases

Last edited by Melon Head; 25th May 2012 at 03:24 PM.
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Old 28th May 2012, 02:30 PM   #472
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Something just occurred to me about the circuit.
I think it is capable of even better performance, just need to wait till tomorrow to confirm it.
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Old 28th May 2012, 02:58 PM   #473
lhquam is offline lhquam  United States
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Quote:
Originally Posted by Melon Head View Post
Something just occurred to me about the circuit.
I think it is capable of even better performance, just need to wait till tomorrow to confirm it.
Before I saw your non-Turbo/Turbo THD plots and did some simulations, I was not convinced about the Turbo. EUVL has proposed an alternative based on reducing the source resistors to near zero, which helps, but increases the problem of bias current vs. temperature.

I am now a believer in the Turbo.
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Old 28th May 2012, 03:05 PM   #474
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Hehehehehehe
If my hunch is right, I will be very happy.
Nelson is very sly.
I feel dumb again (as usual) for not thinking of this immediately.
Very basic stuff. Not rocket science.
Bloody brilliant though

Last edited by Melon Head; 28th May 2012 at 03:10 PM.
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Old 30th May 2012, 04:16 PM   #475
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Quote:
Originally Posted by Melon Head View Post
Hehehehehehe
If my hunch is right, I will be very happy.
Nelson is very sly.
I feel dumb again (as usual) for not thinking of this immediately.
Very basic stuff. Not rocket science.
Bloody brilliant though
My hunch was right. Although the improvement is only subtly better than the original diode results posted earlier.
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Old 30th May 2012, 04:27 PM   #476
EUVL is offline EUVL  Europe
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You are misquoting me I am afraid.

My proposed alternative (in post #42) is not based on reducing the source resistor (only).
The key to my proposal is using MOSFETs with much higher Yfs (e.g. 2SK3497).
That, combined with a reduction in Rsource will give the same current gain as a 2SK1530 plus a diode.

See :
F5 Turbo is posted

And I do not consider 0R33 for Rsource to be low. The F5X uses 0R22 since day one.
Nor have I ever experienced any bias stability at steady state.
Yes, the bias is a bit lower when cold. But once it has warmed up, it stays there.
Assuming of course your heat sinks are properly sized.

And I am still not a believer of the diode.


Patrick
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Last edited by EUVL; 30th May 2012 at 04:37 PM.
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Old 30th May 2012, 04:30 PM   #477
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Are you talking to me Patrick?
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Old 30th May 2012, 04:35 PM   #478
EUVL is offline EUVL  Europe
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I was referring to post #473.


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Old 30th May 2012, 04:43 PM   #479
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Patrick it is very quick and easy to wire a diode into your circuit.
Probably take all of 30 minutes to try it and if you don't like the results take it out.
Just try it.
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Old 30th May 2012, 04:53 PM   #480
AndrewT is offline AndrewT  Scotland
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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.
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