bipolar (BJT) transistor families for audio power output stages

Jump to Latest
L

Lumba Ogir

Banned
Joined 2005
Piercarlo,
The key point that usually few in audio take in adequate count, is what really matter in audio listening: ratios among signals, not their absolute values. A thing usually considered only when facing with compressed music that in reality count EVERLY in ANY audio listening situation. Our earing-brain system should be considered more similar to a "demodulator" instead to a linear adcquiring systems. A "demodulator" which we may figure acting as the old thelephonic modems that, from a stream of "noise" decoded all data we see on monitors when connected to web: images, letters, sounds, and so on.
Click to expand...
Although indistinctly explicated, I agree. You should know that global feedback effectively upset the harmonic relationships that`s why audiophiles primarily dislike it.
 
B

BV

Member
Joined 2005
You should know that global feedback effectively upset the harmonic relationships
Click to expand...
Wrong, it only caused other harmonics structure of distortions of input signal and its harmonics as in amplifiers without GNFB. But here it is usualy in orders more changed..
Can you answer to repeated question, what is your prefered amplifier(s)??
 
W

wahab

Member
Joined 2009
the thread about bjts has been turned as an onslaught of
the global feedback principus...
wether it s good or not, we still don t known ,at least through
this discussion, which bjts are the most adequate for audio..
must i conclude that this choice is not that important, as it
seems for some that whatever their specifications, the bulk
of the resulting amplifier caracteristics will be modeled by
the presence or absence of feedback.
 
T

Telstar

Member
Joined 2007
Lumba Ogir said:
Telstar,

This is not quite clear to me. It is not about noise floor, it is very importantly about harmonic spectrum.
Click to expand...

I reiterate the point that below a certain amount (relative, yes, better to specify it), the ears are not able to hear distortions and therefore they merge with the noisefloor.
Different distortions (not just talking about different armonics) are perceived as greater or smaller in a non linear way and the matter is still under investigation.

That's the reality we are facing. The the ear`s distortion is not a disadvantage in sound reproduction.
Click to expand...

I dont think it is possible to match the ear's own distortion in any amplifier... because one should first know the former with great accuracy, and the scientists dont :)

On the last point (HF distortions), we agree. I say more, that is the main reason why lots of people prefer tube amps.
 
traderbam

traderbam

Member
Joined 2002
andy_c said:
Often the concept of "introducing new distortion products" makes no sense though. Mathematically, if we have a static nonlinearity and can express the input-output relationship as a polynomial, we can by inspection observe the highest-order term of the polynomial and conclude that's the maximum order of the harmonic distortion product. Consider the tanh() function that shows up in BJT diff amp analysis. It has a power series representation, the Taylor series, but that thing has an infinite number of terms. So it generates an infinite number of harmonics. Even though the ones of very high order may be extremely difficult to measure, they are there nonetheless. Therefore the concept of "introducing new distortion products" makes no sense in this case, because a simple diff amp already generates an infinite number of odd harmonics. I haven't tried this, but I doubt that feedback would introduce even harmonics to the mix.

This is by no means an isolated example either. Ever do a DC sweep of an optimally biased class AB output stage in simulation and try to fit the resulting data to a polynomial using least-squares techniques? I tried and gave up at order 9. The results weren't even close. I don't have proof of this, but I've concluded that it's going to take a huge number of polynomial terms, possible infinite, to fit the curve properly. This is due to having small, fine-grained wiggles near the zero crossing (but not discontinuities), in effect straightening out to a gradual bend as the output voltage and current get larger. You can simulate the effects of feedback on this circuit as Bob originally did, producing a Baxandall-like plot of relative harmonic levels vs. feedback. The results of that analysis, found in the Cordell feedback thread, are counterintuitive. Even small amounts of feedback reduce all harmonics, and larger amounts of feedback reduce them more, in a monotonic fashion.

The conclusion is that the effect of feedback on individual distortion components is rather subtle to grasp, highly nuanced and sometimes counterintuitive, depending a great deal on the nature of the open-loop nonlinearity. I'm reminded of a saying by H.L. Mencken. "For every complex problem, there is a solution that is simple, neat, and wrong." Just replace the word "solution" with "explanation" and you describe much of what's been said here about feedback and distortion.
Click to expand...

Hi Andy,
May I clarify my understanding of your post? In essence, you appear to be saying three things:
a) If an open-loop system has an infinite series of harmonics then putting NFB around it will not create any novel harmonics.
b) The distortion products of a single-tone will be monotonically reduced as NFB factor is increased.
c) This is a complicated area to understand.
Is this a fair summary?
Brian
 
Piercarlo

Piercarlo

Member
Joined 2006
Lumba Ogir said:
Piercarlo,
you have filled this thread with highly confused muddy statements, reveling enormous gaps in your knowledge. Maybe you should take a break and gather some information from carefully chosen sources. Then come back and proceed in a cautious and prudent manner.
Click to expand...

If I have enormous gap in knowledge (i'm not an engineer also if I've studied electronic by miself for twenty years). you are, at best, COMPLETELY ignorant. Joking with SPICE and monkeyng technical languages DON'T make an engineer...

Regards...
Piercarlo
 
Piercarlo

Piercarlo

Member
Joined 2006
Dear Lumba Lysenko Ogir.

Your terrifying ignorance, bullshitmanship and megalomany are simply pitious as are your self reputed "technical" claims, Please avoid to rain your shitty and crappy judgements on me or any other forumers: many of us have AT LEAST tried to study electronic basis related to audio equipment and just have had the humilty of earing TRUE engineers (often long time trained engineers and even teachers at university) for really useful advices, not borious, busted and useless copywriter as you are.

Thanks! :)
Piercarlo
 
traderbam

traderbam

Member
Joined 2002
Speaking of quotations, here are a couple that were not made in the context of audio but I think are very apt in the audio world:

“If you can't explain it simply, you don't understand it well enough” :xeye:

“Unthinking respect for authority is the greatest enemy of truth.” :worship:

Guess who? :scratch2:
 
bobodioulasso

bobodioulasso

Member
Joined 2008

Attachments

  • images.jpg
    images.jpg
    3.2 KB · Views: 294
blmn

blmn

Member
Joined 2001
Back to the original question,

Since there are evidences about the good performance of correctly designed amps using old and relatively slow devices at output (fT near 4MHz, as an example). Someone show here a Blameless original design using MJ802/4502 with no more than 0,01%DHT at 20kHz, I´m asking if the sustaining gain capacity at high current demands would be more important than the fT, in these cases.

Any clues?

Regards,
 
You must log in or register to reply here.
Top Bottom