I figured someone might mention that.
FWIW, The Soviets landed on the moon ten years earlier, in 1959 (unmanned). I don't own any late 50's Russian recordings, wonder how they sound?
Feedback acts, in effect, as a complementary filter as it supplies (at the input) approximately the signal you need to get the required output. Anyone who understands control theory will tell you that controlling a loop with a single-pole LP filter or an integrator is easy, but a loop with a genuine time delay is much harder.
I'm not sure whether you would want to call this cancellation or overcoming but the effect is the same. You can't cancel/overcome a genuine time delay without using a time machine. I don't think any audio website is yet offering a room temperature time machine.
I'm not sure whether you would want to call this cancellation or overcoming but the effect is the same. You can't cancel/overcome a genuine time delay without using a time machine. I don't think any audio website is yet offering a room temperature time machine.
As long as they don't forget to convert kilometers into miles
So, we have audio amps with incredible bandwidth, stable on loads that are stupid, DF that is no more than a couple inches of wire, THD, IM, TIM, SID, "LBJ took the IRT down to 4th street USA...." * and yet, there is something that may be known, but I can't point to, that causes some amps to accentuate/create something in reproduction of a trumpet that does not occur live that makes my wife's teeth grate. Considering all the terrible things that happen to a signal from mic to speaker, it baffles me that this last stage has something audible. I guess we just don't know.
I am going to propose to the local dealer that when they have a small Halo out of the box, I being my amps, speakers, "bad" music and my good wife to see if whatever it is has been beaten into submission. It is a relevant datapoint to say it is solved even if we don't know which of thousands of issues solved it. That would be the outcome I expect. Of course, we learn more when the outcome is not what we expect.
Still, I will play with my old junk and see if I can change it. My parts are still not here. ARRRRG. Anyway, I cut out the MDF for a set of speakers for my Nephew. Crossover is modeled as a starting point and a plan for what finishing technique I will try on this set. When all else fails, there's nothing like making sawdust. I will then troll Amazon for a used book or two as referenced. Books may not have the answers, but the good ones have the questions.
* To the young whipersnappers out there and the international readers, my reference is to the 60's musical "Hair" a song titled "Initials."
So, we have audio amps with incredible bandwidth, stable on loads that are stupid, DF that is no more than a couple inches of wire, THD, IM, TIM, SID, "LBJ took the IRT down to 4th street USA...." * and yet, there is something that may be known, but I can't point to, that causes some amps to accentuate/create something in reproduction of a trumpet that does not occur live that makes my wife's teeth grate. Considering all the terrible things that happen to a signal from mic to speaker, it baffles me that this last stage has something audible. I guess we just don't know.
I am going to propose to the local dealer that when they have a small Halo out of the box, I being my amps, speakers, "bad" music and my good wife to see if whatever it is has been beaten into submission. It is a relevant datapoint to say it is solved even if we don't know which of thousands of issues solved it. That would be the outcome I expect. Of course, we learn more when the outcome is not what we expect.
Still, I will play with my old junk and see if I can change it. My parts are still not here. ARRRRG. Anyway, I cut out the MDF for a set of speakers for my Nephew. Crossover is modeled as a starting point and a plan for what finishing technique I will try on this set. When all else fails, there's nothing like making sawdust. I will then troll Amazon for a used book or two as referenced. Books may not have the answers, but the good ones have the questions.
* To the young whipersnappers out there and the international readers, my reference is to the 60's musical "Hair" a song titled "Initials."
Hey tvrgeek,
I keep thinking about all the combinations of stuff that we use. This speaker1 sounds great with that amp1 but with amp2 it sucks while amp2 sounds great with speaker2... if the amp is not designed to drive something specific, it really is a craps shoot.
Can there really be one amp to rule them all? i doubt it.
good luck,
revb.
I keep thinking about all the combinations of stuff that we use. This speaker1 sounds great with that amp1 but with amp2 it sucks while amp2 sounds great with speaker2... if the amp is not designed to drive something specific, it really is a craps shoot.
Can there really be one amp to rule them all? i doubt it.
good luck,
revb.
Soviets had what they called "Scientifically Planned Economy", or what we call now, "Global Economy", when it is possible to throw resources where they are needed for a break-through. American capitalism then was more effective, since people really owned businesses, calculated own money adjusting all decisions to the reality. If money is "theirs" (Central Bank in Soviet Union, or Reserve Bank in Global Economy), things are quite different...
Edit: Tvrgeek, add to your challenge one more thing: Denon AVR-591. It is very cheap amp, but sounds better than many boutique designs. I was surprised when heard it first: i bought it as a donor for it's Audissey DSP, but use almost an year as-is.
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Yeah, first manned orbit of the moon was in '68. Easy peasey compared to landing on it, traipsing around for a bit, launching back off it, and returning safely.
se
Exactly, it is a system. Unfortunately, the industry is split forcing electronic designers and speaker designers to work with a wall between them pointing fingers at each other. Pro sound does a lot of integrated systems, but from what I hear of them at clubs, they are still not really systems, just amps stuffed on speakers. I don't know what it will take to get past the current stalled condition. The market is demanding portability not quality. What has hit the market are really poor powered subs, powered monitors with 10 cent amps, or over the top price that has no market.
A few have tried. Mat Polk was smart enough to know $300 speakers were going to be played on $200 receivers, so he tuned them assuming a high Re. Theil and Keff both tried line level eq boxes and failed in the market. Meridian and Paradigm have tried powered monitors but were out of price range. If I were a venture capital guy, I would not put my money there either, even though I know it is the correct engineering solution.
What it will take is one of you amp guys who understands there is a difference in amps team up with a speaker guy who also understands any old amp won't do. Then bring in a product at a price point that could sell. I won't hold my breath.
Besides, hard for guys to brag how many kazillion watts a system has when the speakers are all "sufficient" and it would remove the excuse for magic wires that cost more than the speakers.
Sy,
Propagation delay in typical Op-Amp type structures is several microseconds, even fully uncompensated comparators usually have propagation delays in the 100's of nanoseconds.
This emphatically is not what I would call "essentially zero", but rather "essentially and significantly non-zero". As such propagation delay clearly exists and is real, I think calling it an "audiophile myth" is rather disingenuous.
IF this propagation matters for the subjective sound quality of audio-circuits is a matter that may be debated, as the propagation delay is just another way of expressing other factors that can have an impact (but are also heavily disputed) one may suggest that low "propagation delay" may be used as an indicator of quality, but I suspect the correlation will be somewhat iffy...
Ciao T
Propagation delay in typical Op-Amp type structures is several microseconds, even fully uncompensated comparators usually have propagation delays in the 100's of nanoseconds.
This emphatically is not what I would call "essentially zero", but rather "essentially and significantly non-zero". As such propagation delay clearly exists and is real, I think calling it an "audiophile myth" is rather disingenuous.
IF this propagation matters for the subjective sound quality of audio-circuits is a matter that may be debated, as the propagation delay is just another way of expressing other factors that can have an impact (but are also heavily disputed) one may suggest that low "propagation delay" may be used as an indicator of quality, but I suspect the correlation will be somewhat iffy...
Ciao T
Hi,
I think there are several questions here.
First, one would would be: In circuits that have looped feedback, spanning multiple stages, are distortions present or possible that are not found in circuits that omit looped feedback and if so, what are they?
Another would be: Is looped feedback around several stages the exact and complete equivalent of using the same amount of degeneration equally distributed across stages in the loop instead?
Still another would be: Is looped feedback around a single stage the exact and complete equivalent of using the same amount degeneration?
Another one would be: If our first question is answered affirmative (incidentally, it is, for around 4 decades), will reducing reducing global looped feedback and increasing local looped feedback or local degeneration reduce the distortions caused by (mis-) applying global looped feedback?
Ciao T
I think there are several questions here.
First, one would would be: In circuits that have looped feedback, spanning multiple stages, are distortions present or possible that are not found in circuits that omit looped feedback and if so, what are they?
Another would be: Is looped feedback around several stages the exact and complete equivalent of using the same amount of degeneration equally distributed across stages in the loop instead?
Still another would be: Is looped feedback around a single stage the exact and complete equivalent of using the same amount degeneration?
Another one would be: If our first question is answered affirmative (incidentally, it is, for around 4 decades), will reducing reducing global looped feedback and increasing local looped feedback or local degeneration reduce the distortions caused by (mis-) applying global looped feedback?
Ciao T
Hi,
In my previous post I vented a bit about the (un) reasons causing these little spats we have all become so fond of watching, now for something a little more constructive...
If you wish to try a few things, do try to take an amplifier that misbehaves in the way you describe and work your way through the schematic, step by step and systematically increasing the local degeneration and stage current (starting in the input stage) and opening the miller compensation suitably to retain similar stability margins (this means you can cannot just reduce the compensation cap tenfold if you reduced OLG by 20dB).
Once you have converted most (if not all) of the global loop feedback into local feedback try listening again. IF you find that the objectionable quality is reduced or gone, we have at least established an empirical link between levels of looped feedback and this peculiar acoustic aberation, or if this quality is unchanged we have established that global looped feedback is not to blame...
It does of course tell us little about the mechanisms, but it leaves us at least with a mitigation strategy. Of course such actual science is not appreciated by some, so be cautious about relating results.
Ciao T
In my previous post I vented a bit about the (un) reasons causing these little spats we have all become so fond of watching, now for something a little more constructive...
If you wish to try a few things, do try to take an amplifier that misbehaves in the way you describe and work your way through the schematic, step by step and systematically increasing the local degeneration and stage current (starting in the input stage) and opening the miller compensation suitably to retain similar stability margins (this means you can cannot just reduce the compensation cap tenfold if you reduced OLG by 20dB).
Once you have converted most (if not all) of the global loop feedback into local feedback try listening again. IF you find that the objectionable quality is reduced or gone, we have at least established an empirical link between levels of looped feedback and this peculiar acoustic aberation, or if this quality is unchanged we have established that global looped feedback is not to blame...
It does of course tell us little about the mechanisms, but it leaves us at least with a mitigation strategy. Of course such actual science is not appreciated by some, so be cautious about relating results.
Ciao T
Basicly , reducing gain with local feedback , i.e , degeneration ,
will be far less efficient than using global feedback to reduce
the gain in the same proportion.
Degeneration waste gain uselessly as it doesnt allow for as
good linearization as global NFB.
Hi,
I am not sure what you mean with "efficient gain reduction"...
That is an interesting assertion, but is it true?
Let us a perfectly theoretical amplifier.
The input stage contributes 1% HD open loop at a given level and has gain of 100.
The VAS contributes 1% HD open loop and has a gain 1000.
The Output Stage is Fet driven (to eliminate loading effects) and contributes 0.3% HD open loop.
So the whole Amplifier open loop will show around 1.45% THD with a fairly rich upper harmonics spectrum, as we have two stages producing "distortion of distortion". And the input stage will have a miniscule linear range as well...
With 10MHz GBP we now find we need a 100Hz open loop bandwidth so we already loose 20dB overall loop gain at 1KHz, though this gain is turned into 20dB local loop feedback IF we use miller compensation. DC Gain is 100dB.
Closed loop gain is 20, so we get around 0.002% HD at 1KHz, but again, heavily weighted towards upper harmonics and poorer linearity at upper frequencies.
Now let us degenerate the Input stage by 10dB and the VAS Stage by 10dB. So our 1% HD becomes 0.33% HD for each stage and we have 0.57% HD open loop and for 10MHz GBP we have 1Khz open loop bandwidth. Our Open loop gain from DC to the open loop bandwidth is 10,000. Once we close the loop we have 0.001% HD...
Of course, the above is merely a "milkmaid" calculation and things are more complex in reality, but it seems for a classic SS Amp judiciously adding local degeneration can actually reduced the final THD, so one may say that there are circumstances where local degeneration is more efficient at reducing distortion than global looped feedback, while at the same time improving transient distortion behaviour.
Of course, anyone who bothered to read Self, Cordell, Ottala, Gilbert et all knows that anyway, so apologies to most here for belabouring things this much.
Ciao T
I am not sure what you mean with "efficient gain reduction"...
That is an interesting assertion, but is it true?
Let us a perfectly theoretical amplifier.
The input stage contributes 1% HD open loop at a given level and has gain of 100.
The VAS contributes 1% HD open loop and has a gain 1000.
The Output Stage is Fet driven (to eliminate loading effects) and contributes 0.3% HD open loop.
So the whole Amplifier open loop will show around 1.45% THD with a fairly rich upper harmonics spectrum, as we have two stages producing "distortion of distortion". And the input stage will have a miniscule linear range as well...
With 10MHz GBP we now find we need a 100Hz open loop bandwidth so we already loose 20dB overall loop gain at 1KHz, though this gain is turned into 20dB local loop feedback IF we use miller compensation. DC Gain is 100dB.
Closed loop gain is 20, so we get around 0.002% HD at 1KHz, but again, heavily weighted towards upper harmonics and poorer linearity at upper frequencies.
Now let us degenerate the Input stage by 10dB and the VAS Stage by 10dB. So our 1% HD becomes 0.33% HD for each stage and we have 0.57% HD open loop and for 10MHz GBP we have 1Khz open loop bandwidth. Our Open loop gain from DC to the open loop bandwidth is 10,000. Once we close the loop we have 0.001% HD...
Of course, the above is merely a "milkmaid" calculation and things are more complex in reality, but it seems for a classic SS Amp judiciously adding local degeneration can actually reduced the final THD, so one may say that there are circumstances where local degeneration is more efficient at reducing distortion than global looped feedback, while at the same time improving transient distortion behaviour.
Of course, anyone who bothered to read Self, Cordell, Ottala, Gilbert et all knows that anyway, so apologies to most here for belabouring things this much.
Ciao T
This , is where your logic stop being relevant as you re assuming
that degeneration has the same properties as GNFB , wich is not true.
Reducing a stage gain by a factor of 10 dB by increasing
degeneration will not reduce this stage distorsion by the same
factor , as is the case with GNFB , wich is what i pointed
in the post above.
Also , about miller compensation , you re downplaying the fact
that not only it reduce the open loop gain bandwith but that
at the same time this lost gain is in fact used to create
a local feedback loop that will inherently reduce the distorsion
of this stage.
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