John Curl's Blowtorch preamplifier

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#15,102
audiowolf said:
Hey John,
Check out that Krill thread...Ive been over there all afternon myself!
Note that it is not in any way related to Krell..

If I remember correctly, krill is whale and fish food, including plankton, and is the base of the food chain on the oceans. There may be a double meaning or some sort of pun hiding in there, perhaps not, but I am always looking for such word-play.

Woff, AND Howl! [ If you hang around long enough, your GONNA learn SOMETHING new!]
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I think you are on to something. Now tell us who the Krell were.
 
#15,103
mjf said:
Originally posted by Edmond Stuart
Nevertheless, no one would call this class-A or class-AB operation.

hello.
may i call it:
class b with a small amount of bias
greetings.........
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Of course you may call it that way. 🙂
BTW, there exists another topology, which has similar properties. It's based on the squared-law relationship between Ids and Vgs of FETs.
It was published in WW+EW, a couple of years ago.


Regards,
Edmond.
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#15,106
lumanauw said:


Hi, Steve,

Diamond voltage gain and diamond buffer output stage? There's a recent good reviewed power amp using these called "DartZeel"
http://www.diyaudio.com/forums/attachment.php?s=&postid=227250&stamp=1062004300
It also force classA on output stage, but by using forward diodes at base, so the base charge easy to come in and difficult to come out. Is this enhance classA the same result as your method (not using base bleeder resistor at all) ?
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No, that is not the same as mine, however that can be done with small signal transistors to build a really wide bandwidth voltage amp.
 
#15,107
I agree the original Krill thread is more a constructor's thread now & not about the explanation or theory of operation.

BTW, the explanation of the circuit was given by Steve near the beginning of that thread
The base current in the bias pair is equal in both transistors at all times. I is not, however constant. Changes in the emitter current cause changes in the base current. When one transistor conducts less, the other conducts less. If for example Q8 conducts less because the voltage on the emitter of Q7 goes more positive (causing more current to flow in the base of Q13) then Q11 conducts less causing a greater voltage drop from emitter to collector. This makes more current available to the base of Q15 causing greater conduction to maintain an on state.
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Alansawyer, anything that avoids crossover, avoids dynamic crossover distortion, no?
 
#15,108
scott wurcer said:


I'm willing to give it a try, but that thread was hard to read with almost daily corrections to the schematic and they have gotten away from the basic theory.
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At some point in that thread I address the issue of those mistakes needing correction. Try to keep in mind that I had been "away", so to speak, for a while when I was talked into posting some of my work. I had not even turned on my computer for over a year and I was, and still am, a little rusty.
 
#15,112
Steve Dunlap said:
This will be my last post in this thread about my amp. I will be happy to discuss it in the Krill thread.

Will someone please point out out where I make a big deal about this being a class A amp?
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Steve,
I don't think it is you.
It's others that seem to make the claim and Glen's example was pointing out the error of their obscure definition on "non switching" which has nothing to do with ClassA
 
#15,113
syn08 said:


I can't find any 400W, 20KHz or relevant measurements in that thread. It doesn't seem the Krill went anywhere beyond a concept, but then I might be wrong. Steve claimed measured performances, I'm willing to discuss about, there or in a new thread.
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If you'll read the thread you'll see that 100 units were sold, all but one alive and kicking .

Which is one more reason why all discussions of the Krill design should be on the krill thread.
 
#15,114
MJL, as far as temperature is concerned:
Class A HOT at idle, reducing with higher power out.
Class AB-1 Medium Hot at idle, Medium Hot at full output. Slightly wavy temp curve.
Class AB-2 Almost cool at idle, rising in temperature, much like Class B
Class B, cool at idle, rising to max temp with 4/10 power and then staying there or reducing in temperature at full output.
 
#15,115
By scott wurcer - This is interesting. Your first plot seems to show some non-linear charge storage effects, not surprising with high current lowish Ft devices
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You are right on.. plot 1 shows the charge "suckout" cap's
effect at HF (negative hook). Both plots were biased at exactly
100ma. Plot 2's corners were rounded and never completely
shut off.

I am surprised all were not aware of the "big K" (krill)
I never saw it as class A even through technics and a few others
threw that in for marketing reasons.This topology is in a
class by itself but is similar to technic's "super a".

Susuma Tanaka seems to be the greatest source of info on
this technique as outlined on his paper ... http://71.203.210.93/upload/
"Tanaka AES.pdf" is the file.. (gift from diy members)
,he even calls it "new biasing for class B" so there was never
a claim of class A. 😕
I am busy with the "dartzeel" now and am VERY impressed.
OS
 
#15,116
john curl said:
MJL, as far as temperature is concerned:
Class A HOT at idle, reducing with higher power out.
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I struggled with this early on (well, early on for me, anyway). If I want to figure class A bias, I'll calculate the max output current demand per device into the given load then set the DC bias to exceed this.
This has the outputs dissipating (burning, wasting) this current. The input signal triggers it to proportionally flow to the load, so the load gets hot and the outputs cool (a bit) as they are no longer burning off the current, but delivering it. Is this correct?
 
#15,118
john curl said:
The equations are in an old textbook 'Electronic Engineering' by Alley and Attwood. A text that I learned from, in the '60's. Never completely forgot it, and it MIGHT imply where I usually set my optimum power amplifier bias point.
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We have that in common: we both learned something in the 60's - I learned to walk and not pee in my pants...🙂

You bring up a good point earlier, how the devices have become faster. Looking at the output of one of my cobbled together amps, I have never seen notable crossover distortion (in a properly working example). This would be with next to no idle current.
 
#15,120
MJL21193 said:



I struggled with this early on (well, early on for me, anyway). If I want to figure class A bias, I'll calculate the max output current demand per device into the given load then set the DC bias to exceed this.
[snip]
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I'm not sure I understand you correctly, but the class A output current normally is twice the device bias current. Is that what you mean?

Jan Didden
 
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