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Old 30th May 2012, 07:55 PM   #491
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Originally Posted by EUVL View Post
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.


Patrick
Does the Hump sound like the Klunk?
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Old 30th May 2012, 07:57 PM   #492
EUVL is offline EUVL  Europe
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Please go ahead. I am not stopping you by any means.
I personally have no desire to take on the challenge of adding an exponential device to a quadratic one.


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Old 30th May 2012, 08:04 PM   #493
EUVL is offline EUVL  Europe
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Since we are on the topic, I have another suggestion for those who want challenges.
Forget about the diode and use a 22000uF cap to parallel the source resistor.
6.3V is probably enough voltage.

Takes you 10 minutes to try ?
And ask the tube guys what they think.




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Last edited by EUVL; 30th May 2012 at 08:11 PM.
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Old 30th May 2012, 09:10 PM   #494
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THanks. That confirms my thoughts about what is happening here. I am shocked you are willing to even speak of tubes. Dinosaur lovers.
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Old 30th May 2012, 09:13 PM   #495
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This implies that the diodes have already turned on at the normally recommended Ibias level of ~600mA, ie. zero output current level.
Most will have realised that my 800mA should have read 600mVrs, the bias voltage across the source resistor.

It should read:
This implies that the diodes have already turned on at the normally recommended bias level of ~600mVrs, ie. zero output current level.
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Old 30th May 2012, 09:41 PM   #496
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I think to view this properly, you have to consider what the degeneration resistor is doing, how what it is doing is affected by the AC signal through it, and what if the effect of this AC signal was being mitigated by either a diode, or a cap asa Patrick suggested. I ran headlong into this subject when i was trying to figure out Juma's preamp version of the F5. Got me looking into degeneration and what is actually happening.
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Old 30th May 2012, 09:41 PM   #497
EUVL is offline EUVL  Europe
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Re #493, you can read all about the cap in Horowitz & Hill 2nd Edition Section 2.13 "Bypassed emitter resistor".
Or John Linsley Hood 1997 Valve & Transistor Amps Fig. 3.3c & associated text.

A cap has an advantage over the diode in that it only acts for AC.
So the DC bias is totally determined by the Rsource itself, as it should.
For AC signal, the cap is always effective as long as it is large enough in value to guarantee low corner frequency.

Not the case for the diode.


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Last edited by EUVL; 30th May 2012 at 09:45 PM.
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Old 30th May 2012, 11:41 PM   #498
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Patrick
What about the biasing thermistor? There is plenty of non-linearity there too.
Are you also suggesting the patented Aleph Current Source is also a stupid idea?
What about a current source paralleled on one of the mosfets of a push pull output stage used on an Amp worth $65,000?
There is also some weird crap going on there too.
I notice PASS LABS are still in business.
According to your thinking they are incompetent, amplifier builders.
That may not be your intent, but your ideas and thinking are definitely implying that view.
There are plenty of text books that have opposing views on things.
There are also plenty of authors of text books who don't make amplifiers for a living.
Come on Patrick.
I understand your concerns about the diode, but I'm not giving in that easy.
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Old 30th May 2012, 11:56 PM   #499
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Quote:
Originally Posted by EUVL View Post
Re #493, you can read all about the cap in Horowitz & Hill 2nd Edition Section 2.13 "Bypassed emitter resistor".
Or John Linsley Hood 1997 Valve & Transistor Amps Fig. 3.3c & associated text.

A cap has an advantage over the diode in that it only acts for AC.
So the DC bias is totally determined by the Rsource itself, as it should.
For AC signal, the cap is always effective as long as it is large enough in value to guarantee low corner frequency.

Not the case for the diode.


Patrick
Hey, Thats what I said, well not really, but thats what I was eluding to. Melon Head, the ACS is nothing special. Anybody could have come up with it.....after looking at!
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Old 31st May 2012, 12:00 AM   #500
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