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The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
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Old 8th December 2018, 02:15 PM   #341
Hans Polak is offline Hans Polak  Netherlands
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Join Date: Mar 2005
Location: Blaricum
Quote:
Originally Posted by maxlorenz View Post
Ah! very interesting. I tried to connect that way the second cascoded BJT but it cannot be done. Is it right to have a voltage output instead of a current output? Can they be compared?
Of course in your case it's the current output that counts, but I was just curious to repeat the test that Kolinummi describes in his book.
And there was no overlap with my finding, so be careful to follow an unconfirmed advise.
Quote:
Unfortunatelly, when I tried the gate-to-emitter mod on the "QUAD" the stability margin decreased and the THD deteriorated several orders of magnitude...
Are you referring to a real measurement of the complete amp? In that case the cause might be that your Fets do not have a source voltage of -4.2 Volt but quite a bit less, leaving not enough room left to connect the gates to the emitters.
But when simulating, there is no visible difference between the two for a complete amp.

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Anyway, isn't the whole arrangement (bootstrapped cascoded-CFP) susceptible to thermal analysis? Can you see what happens to the JFET?
As I understand, it is not the absolute value of thermal production but the alteration of it following the non constant musical signal. Maybe non-periodic bursts of square waves could show something useful...
No, not the whole input stage arrangement is susceptible to TP, because Q3 and Q4 have full control.
And as explained in previous the TD sims, I was only looking at the effect of a periodic burst, the steady state power consumption was subtracted.
When looking for instance at the dual bootstrap image in #334, you will see in the top that 3.2155465mW was subtracted, being the steady state power consumption.


Hans
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Old Yesterday, 12:36 PM   #342
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by Hans Polak View Post
Are you referring to a real measurement of the complete amp? In that case the cause might be that your Fets do not have a source voltage of -4.2 Volt but quite a bit less, leaving not enough room left to connect the gates to the emitters.
But when simulating, there is no visible difference between the two for a complete amp.
Simulations only. I'm busy with other projects at the moment but I might try it later...

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Originally Posted by Hans Polak View Post
No, not the whole input stage arrangement is susceptible to TP, because Q3 and Q4 have full control.
And as explained in previous the TD sims, I was only looking at the effect of a periodic burst, the steady state power consumption was subtracted.
When looking for instance at the dual bootstrap image in #334, you will see in the top that 3.2155465mW was subtracted, being the steady state power consumption.

Hans
Now I understand better. Thank you very much for the explanation.
Then one of the versions shows no delta T when pushed. Please upload the circuit that performs so well. Remember I have updated many times with the same name...

On the mean time, I made my mind about the non optimized "Bootstrapped-Darlington" output: on stock form it performs quite well and is much easier to stabilize and has much fewer parts than the "QUAD"; it is a tad less dynamic and little less defined, and it is "darker" sounding. To my amazement, when I performed the RDRD string mod, the focus and definition improved a lot, practically on par with the "QUAD". Unfortunately, it lacked instruments separation, depth of image and definition of the melodic lines compared to the official Amnesis, but I am sure it would be totally satisfactory for someone not acquainted with the best version. I am not expert on Darlington circuit so I imagine it can be perfected...it is so simple that it would be a shame not to use it...

Which takes me to the working hypothesis for the output (driver buffer and output section), which must be able to exploit the putative benefits of the input section (whichever the mechanisms involved) for which function it must be fast and linear and more...that lend me to explore cascodying and then bootstrapping, that apparently deals with Early effect (base width modulation) but also has a positive feedback effect by injecting the signal (or a buffered sample of it) to the base/gate. I detected a correlation between this bootstrap and dynamics: the more bootstraps in the amp, the more micro and macro-dynamics...and the more unstable it becomes : I could be completely off here but it is nevertheless an interesting concept.
Anyway, when you build the thing you will be able to analyze it with better equipment than that I have and listen to it and tell me that I am a complete fool or whatever you like

Best wishes,
M.
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Old Yesterday, 06:49 PM   #343
Hans Polak is offline Hans Polak  Netherlands
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Join Date: Mar 2005
Location: Blaricum
Quote:
Originally Posted by maxlorenz View Post
Now I understand better. Thank you very much for the explanation.
Then one of the versions shows no delta T when pushed. Please upload the circuit that performs so well. Remember I have updated many times with the same name...
I have used these two versions, the Dual and the Triple Bootstrapped versions. See image below. From a thermal point of view, the Dual version performed much better.


Quote:
Which takes me to the working hypothesis for the output (driver buffer and output section), which must be able to exploit the putative benefits of the input section (whichever the mechanisms involved) for which function it must be fast and linear and more...that lend me to explore cascodying and then bootstrapping, that apparently deals with Early effect (base width modulation) but also has a positive feedback effect by injecting the signal (or a buffered sample of it) to the base/gate. I detected a correlation between this bootstrap and dynamics: the more bootstraps in the amp, the more micro and macro-dynamics...and the more unstable it becomes : I could be completely off here but it is nevertheless an interesting concept.
Anyway, when you build the thing you will be able to analyze it with better equipment than that I have and listen to it and tell me that I am a complete fool or whatever you like
The most noticeable effect of bootstrapping is that Cbc will be carrying a very much smaller AC component, thereby decreasing the input capacity.
Especially output drivers can have large (non linear) Cbc capacities that will be significantly reduced by bootstrapping, increasing the Bandwidth and reducing the distortion.


Hans
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