My belief is that local feedback can improve sound quality if used judiciously. I never bought into the feedfoward jig, although, to be fair, the only sample of it I ever heard was a long time ago, by an unkown manufacturer now long gone.
The key word is judicously. A long time ago, before the Internet, I read a paper by Harman/Kardon in which they explained at some length that input stage differential pairs should have local degenration. but should be left to amplify by no less than 5:1. They listed their reasons, which frankly I no longer remember, but it seemed very convincing to me, so I stuck to it.
How else could I get away with 20-26 dB of global NFB otherwise and still have less than 0.05% at rated power into 4 Ohms?
The key word is judicously. A long time ago, before the Internet, I read a paper by Harman/Kardon in which they explained at some length that input stage differential pairs should have local degenration. but should be left to amplify by no less than 5:1. They listed their reasons, which frankly I no longer remember, but it seemed very convincing to me, so I stuck to it.
How else could I get away with 20-26 dB of global NFB otherwise and still have less than 0.05% at rated power into 4 Ohms?
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Yes , I agree that fancy VAS local feedback "tricks" get better measurements
with possibly inaudible SQ improvements.
But , there are other factors that are not subjective.
- mitigating the shortcomings of the silicon (early effect ,capacitances,
saturation).
-using less current to get even more performance.
-why not reduce THD to where it does not matter ? And get a
longer lasting very low THD design , too.
You could "subjectively" improve SQ with a glass of wine ? Huh ?
PS - my VAS actually gets colder at a hard clip. Does this by design.
Also uses less current from the preceding stage.
OS
with possibly inaudible SQ improvements.
But , there are other factors that are not subjective.
- mitigating the shortcomings of the silicon (early effect ,capacitances,
saturation).
-using less current to get even more performance.
-why not reduce THD to where it does not matter ? And get a
longer lasting very low THD design , too.
You could "subjectively" improve SQ with a glass of wine ? Huh ?
PS - my VAS actually gets colder at a hard clip. Does this by design.
Also uses less current from the preceding stage.
OS
Quite usual. And not an argue, as some can reply that your VAS is colder only in a situation that have never to occur.
I tend to agree!
BTW check this out: After This Audio Illusion, You'll Never Trust Your Ears Again | Gizmodo Australia
Jan
That i why some people are more sensible to certain forms of distortions. When their brain knows how they sound, they recognize-them.
Not one of mine, but for anyone interested there is a listening test running here,
http://www.diyaudio.com/forums/lounge/272900-blindtest-between-sample-rates.html
http://www.diyaudio.com/forums/lounge/272900-blindtest-between-sample-rates.html
There is plenty of discussion about THD and other distortions lately/previously.
Over the past week or so I have been experimenting with a 2.4Ghz wireless digital audio link/sender system - Buy 2.4Ghz USB Audio Sender | Read Reviews | Dick Smith Online Shopping
The receiver utilises a tlv320aic3104 as decoder/dac.....a versatile device indeed.
This RCA output receiver does have problems such as system noise, and an SO8 smd 4558 as SD balanced output dac filter/output driver.
Interestingly the pcb has DIP8 pads in parallel with the SO8 pads so is ripe for opamp rolling.
Anyway, initially I have experimented with improving the jitter of the oscillators/crystals in the Thumb Drive size transmitter.
I also purchased a second T/R set so that I can readily do A/B comparisons of modified/factory transmitters and receivers.
Remarkably, cleaning the transmitter jitter turns this link system from a midfi turd, to very listenable/enjoyable indeed, and the wireless functionality is just magical....ie from my sunroom I can run Foobar (including polarity switching) and play any music I feel like without getting off my date !.
The wireless receiver feeds a Behringer Mic/Line preamp (Mic2000) balanced driving a pair of Behringer B2031 active speakers (modded internal damping and driver wiring but deliberately no electronic mods...yet).
The takeaway here is that the distortion performance of the system is not spectacularly good, BUT fixing jitter changes everything and removes a whole layer of distortions/products that do not belong.
John C, I strongly suspect that jitter is what you object to when evaluating digital sourced systems, and gives credence to your (and others) preference for vinyl.
Digital playback does not have to be subjectively bad, and jitter per se is not necessarily the show stopper, BUT the jitter spectrum very much is.
Jocko is entirely correct...jitter and especially jitter spectrum is everything when it comes to digital playback.
Dan.
The extension of this discussion is of course the damage done by AD conversion process timebase jitter...comments welcome.
Over the past week or so I have been experimenting with a 2.4Ghz wireless digital audio link/sender system - Buy 2.4Ghz USB Audio Sender | Read Reviews | Dick Smith Online Shopping
The receiver utilises a tlv320aic3104 as decoder/dac.....a versatile device indeed.
This RCA output receiver does have problems such as system noise, and an SO8 smd 4558 as SD balanced output dac filter/output driver.
Interestingly the pcb has DIP8 pads in parallel with the SO8 pads so is ripe for opamp rolling.
Anyway, initially I have experimented with improving the jitter of the oscillators/crystals in the Thumb Drive size transmitter.
I also purchased a second T/R set so that I can readily do A/B comparisons of modified/factory transmitters and receivers.
Remarkably, cleaning the transmitter jitter turns this link system from a midfi turd, to very listenable/enjoyable indeed, and the wireless functionality is just magical....ie from my sunroom I can run Foobar (including polarity switching) and play any music I feel like without getting off my date !.
The wireless receiver feeds a Behringer Mic/Line preamp (Mic2000) balanced driving a pair of Behringer B2031 active speakers (modded internal damping and driver wiring but deliberately no electronic mods...yet).
The takeaway here is that the distortion performance of the system is not spectacularly good, BUT fixing jitter changes everything and removes a whole layer of distortions/products that do not belong.
John C, I strongly suspect that jitter is what you object to when evaluating digital sourced systems, and gives credence to your (and others) preference for vinyl.
Digital playback does not have to be subjectively bad, and jitter per se is not necessarily the show stopper, BUT the jitter spectrum very much is.
Jocko is entirely correct...jitter and especially jitter spectrum is everything when it comes to digital playback.
Dan.
The extension of this discussion is of course the damage done by AD conversion process timebase jitter...comments welcome.
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At what point in the circuit did you measure jitter? How was that measurement done?
What was the amount of jitter and its spectrum before you made your unspecified changes? What were they afterward?
Except that vinyl has atrocious timing uncertainty giving plenty of spectral spread (FM and AM) at sub Hz frequencies. All I hear from folks is that like speaker distortion it's just "different" and does not matter. BTW the actual measurement would surprise you.
Like I said modded and factory units for comparison.
Swapping transmitter units takes seconds so audio memory or lack thereof is not a problem/deal breaker.
Foobar makes playing the same passage repeatedly in order to discern differences trivially easy .
I trust my ears, perhaps yours are not up to the task....and so I have heard on the grapevine.
Dan.
Perhaps the relatively slow speed variations, despite the magnitude is the key to vinyl acceptance by some.
TT playback speed variation causes modulation products that are in lower spectrum than typical oscillator stage modulation products, and therefore less modulation products in the Fletcher Munson curve peak aural sensitivity range.
Wow and flutter produce identifiable but reasonably subjectively dis-regardable artifacts.
DA convertor oscillator spectral noise causes a noise cast over the reproduced digital audio......bass loses definition/tightness, mids/vocals get distorted/noised and highs become white noise in nature according to the timebase uncertainty spectrum.
Once oscillator modulation noise is heard and noted it is not forgotten.
Dan.
Treating both T and R brings maximum benefit.
Treatment is proprietary for now, very proprietary....sorry about that.
That said this technique works on all systems from iPod through to stadium systems...and other applications also.
In due course all will be revealed.
Dan.
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