Current feedback - not suitable for audio ?

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#81
4fun said:


Oh well, I just tried to lighten up the heated discussion a bit.

Ok, my humble abstract opinion on witch i think this discussion is about:

A current source is not entirely a current source but also to a lot lesser extent voltage source.

A voltage source is not entirely a voltage source but also to a lot lesser extent a current source.

Therefore both can described be their opposite nomenclature.

The same thing can be said by current feedback and voltage feedback.
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http://www.diyaudio.com/forums/showthread.php?postid=425299#post425299
 
#82
4fun said:


I agree we have an ideal theoretical model and real implementations.
Still it is usful to include as many trees as possible i the theoretical forest.
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Sure, but it is on the other hand often good to keep tha basic building blocks to a minimum and define the others as subcircuits made of from such basic building blocks. That's why we usually don't have both an ideal voltage source and a voltage source with an inner resistance, since we can "build" the latter from an ideal voltage source and a resistor.
 
#83
Mike, since you think more or less everybody are wrong, including Walt Jung, it would be interesting to read an article signed by you in the subject.

I'm pretty satisfied with the theories Walt Jung and others have presented. I'm also satisfied with the results I have achieved so my point of view is that I think CFB is very suitable for audio.
 
#84
It seems to me that there is no definitive answer to the original question. VFB and CFB or any combination (which EVERY implementation is in a real circuit) are ALL suitable for audio.

You choose the node impedance of your subtractor to optimise the sound quality based on the specific choice of parts and what you believe to be the drivers of sound quality. As this is a system problem there are endless combinations of parts to consider. To prove that a particular combination is always best is impossible.

So the better debate might be about what the tradeoffs are between different subtractor designs with specific parts, and to argue the problems or benefits of different summing node impedances using these parts.
 
#85
Re: Re: Current feedback settling time and thermal tails

mikeks said:


This is plausible in principal because a properly balanced diff. stage suppresses even harmonics at the expense of odd ones....

Be that as it may, this is essentially academic, as the relative quantities of ALL harmonics are (or should be) negligible in well-designed front ends...
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I've noticed that some CFB amplifiers (AD811, AD846) have strange 2nd, and 3rd harmonic plots compared to VFA's (AD826, etc). I'm not sure though if this is just relates to the configurations measured in the datasheets.

If the relative 2nd and 3rd harmonic distortion changes with freqeuncy won't this change the sound of the amplifier ?

Does CFB have a "tube sound" ?
 
#90
Open loop distortion is rather uninteresting I think.

The measurement figures were not simulations, the real stuff, measured by a real good sound card.

The loads I have used can be found here:
http://www.sjostromaudio.com/hifi_files/qrv/qrv08_testreport/qrv08_testreport.html

The test setup isn't optimal because I'll get a hum pick up. The amp is abolutely silent and hum free when I use the headphones.

The result is that the amp is better than the sound card I have used.
 
#95
Open loop distortion is rather uninteresting I think.
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I find it very interesting.
I noticed on your load tests with 100-ohm load that the THD+noise and IMD spectra appear to show distortion in the low to mid -80dBs and low frequency noise at -75dB (the hum you mentioned?). Distortion appears to be around -85dB rather than -100dB. I may be misunderstanding the graphs.
 
#97
mikeks said:
quote:
peranders said:
Mike, since you think more or less everybody are wrong, including Walt Jung........
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So...do you think this true?

From Jung:
quote:
...a unity gain buffer connects the non-inverting input to the inverting input..
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[/B]
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I can't resist.

Attached, Mr. Knowitall, you'll see a simplified schematic of an input stage of a so called CFB opamp .
You won't tell me that there is no unity gain buffer between the + and - input, do you?

I think Mr. Jung does know quite enough about opamp's even if he was not the designer of these AD products.

Enjoy, Tino
 

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#100
zinsula said:
I can't resist.

Attached, Mr. Knowitall, you'll see a simplified schematic of an input stage of a so called CFB opamp .
You won't tell me that there is no unity gain buffer between the + and - input, do you?

I think Mr. Jung does know quite enough about opamp's even if he was not the designer of these AD products.

Enjoy, Tino
Click to expand...

Now, i can't resist, it does exactly what an opamp is supposed to do, amplify the difference between + and - input. Your circuit will have identical collector currents for q2/q3 if both inputs have the same voltage... no unity gain, zero gain 🙄

Mike
 
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