"Local feedback" is one of those stupid designations. Feedback has to be a loop, there is not any feedback within a single device.
It is possible but the question is does the same amplifier with gnfb added sounds better, I guess is does.
Zero output impedance is trivial with just a bit of PCFB.
With only NFB it is also trivial to reduce it to much below the impedance of the connecting cables. So, in a practical feedback amplifier it is as good as a practical zero.
To the best of my knowledge no DBT has ever established the audibility of harmonic distortion below 0.1%. If anyone can prove differently, now is a good time to do so. And finally establish a threshold of audibility, represented by a number. Instead of pontificatingly handwaving and quoting Bruno, the God of feedback.
Surely, there is no shortage of DBT lovers in this thread. Where is your number?
At what level of distortion do amplifiers qualify as "competently" designed and essentially sounding all the same?
I hope the answer will prove that a $200 Rotel sounds much better than a $200k D'Agostino and then we can merrily get into more productive hobbies like knitting.
Yes, feedback is a loop and can be applied locally by using simple arrangements like emitter resistors for common emitter configurations. The feedback occurs as an additional voltage increase whose value is dependent on base_current * transfer_ratio. With such an arrangement, a signal source needs to supply a higher voltage for the same Ic. This is negative feedback.
Another way while still using a common emitter configuration is a resistor connected between the collector and base. Since, Vc decreases with Ib increasing, the contribution to base current from this resistor works in opposition to an increasing signal. This is negative feedback.
The third one, I can recall from my clanky memory, is a common collector configuration where the voltage gain is almost unity. Since, the load is connected between ground and emitter, it acts like an emitter resistor and provides negative feedback.
A transistor connected to nothing still has feedback mechanisms built in due to its own construction out of multiple layers of doped silicon layers.
Any good book about electronics explains these. I am not writing anything out of this world.
Another way while still using a common emitter configuration is a resistor connected between the collector and base. Since, Vc decreases with Ib increasing, the contribution to base current from this resistor works in opposition to an increasing signal. This is negative feedback.
The third one, I can recall from my clanky memory, is a common collector configuration where the voltage gain is almost unity. Since, the load is connected between ground and emitter, it acts like an emitter resistor and provides negative feedback.
A transistor connected to nothing still has feedback mechanisms built in due to its own construction out of multiple layers of doped silicon layers.
Any good book about electronics explains these. I am not writing anything out of this world.
Talking about Strawmen....
The thread title is "Global Feedback - A huge benefit for audio"
Why the hell are we arguing whether Emitter degeneration is feedback or not?
If you cannot close or open deliberately a loop, there is nothing to discuss whether it is useful, a benefit or a nemesis. We can't do anything about it anyway in that case.
But it shows me that many people here are just interested in the academic discussion regardless of audibility etc.
The thread title is "Global Feedback - A huge benefit for audio"
Why the hell are we arguing whether Emitter degeneration is feedback or not?
If you cannot close or open deliberately a loop, there is nothing to discuss whether it is useful, a benefit or a nemesis. We can't do anything about it anyway in that case.
But it shows me that many people here are just interested in the academic discussion regardless of audibility etc.
So what about the papers of Mauro Penasa?
No one interested to comment, even those who explain that "Back EMF" doesn't exist? They certainly have enough knowledge to competently review Mauro's work?
No one interested to comment, even those who explain that "Back EMF" doesn't exist? They certainly have enough knowledge to competently review Mauro's work?
Correct @N101N
Otherwise, a resistor divider would be a feedback device.
Feedback requires a loop as you stated earlier.
Otherwise, a resistor divider would be a feedback device.
Feedback requires a loop as you stated earlier.
I recently modified a pair of 'Pultec' EQP-1A valve/passive (LRC) studio EQ's
swapping the PEC carbon pots for 23 position rotary switched resistors,
obviously same value. Some of the resistors were MF some were CF.
This modification made a difference to the sound which I could clearly
discern. I'm not sure what level the distortion components are of a carbon
track potentiometer but I'm guessing although pretty low it would be
certainly higher than MF and probably higher than CF resistors.
TCD
Feedback occurs when a part of the output finds itself aiding or resisting the input. Feedback has nothing to do with human intervention: it can occur naturally as in a silicon crystal structure. The latter, cannot be avoided, it is intrinsic to the crystal. Any circuit designer has to take account of such feedback when a transistor is used for very high frequencies.
All transistors have an upper frequency limit imposed on them by their natural negative feedback mechanism which cannot be avoided. This is known as the transition frequency.
Well known transistor equivalent circuits explain this clearly.
All transistors have an upper frequency limit imposed on them by their natural negative feedback mechanism which cannot be avoided. This is known as the transition frequency.
Well known transistor equivalent circuits explain this clearly.
"Feedback occurs when a part of the output finds itself aiding or resisting the input."
Sounds to me exactly what an emitter degeneration resistor does.
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On the audibility of distortion below 0.1%:
The problem with the ZGFB amps is that they never are 0.1% at full power and with a real load. They more often than not 5-10x this figure on steady state sine wave tests at mid to high power.
Now consider what happens when you include a real-world speaker load with Zload varying considerably over frequency and often especially low in the critical 200-500 Hz band. The result is more distortion.
Then look at the Frequency response. Getting flat response out of an amp is not actually easy. Typically there is some output variation because Zo is finite - but some of the ZGNFB are all over the place in this regard.
The other one is IMD - a food example of which was posted earlier on this thread.
You can root around in the Stereophile review archives - plenty of examples.
Sounds to me exactly what an emitter degeneration resistor does.
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On the audibility of distortion below 0.1%:
The problem with the ZGFB amps is that they never are 0.1% at full power and with a real load. They more often than not 5-10x this figure on steady state sine wave tests at mid to high power.
Now consider what happens when you include a real-world speaker load with Zload varying considerably over frequency and often especially low in the critical 200-500 Hz band. The result is more distortion.
Then look at the Frequency response. Getting flat response out of an amp is not actually easy. Typically there is some output variation because Zo is finite - but some of the ZGNFB are all over the place in this regard.
The other one is IMD - a food example of which was posted earlier on this thread.
You can root around in the Stereophile review archives - plenty of examples.
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Feedback does occur in the silicon crystal structure, but that denotes something else. In the sense of circuit topology, feedback requires the presence of subsequent device(s).
