Arghhh,
.........................for once I find myself in agreement with Grey.😉 .....on the other hand Mr.Curl is almost never wrong in my experienc.........although I have some reservations about his nob-audio related pursuits.😀 😀 😀
Jam
.........................for once I find myself in agreement with Grey.😉 .....on the other hand Mr.Curl is almost never wrong in my experienc.........although I have some reservations about his nob-audio related pursuits.😀 😀 😀
Jam
Pity poor Neophyte.
Having heard horror tales about 'mind control' and sales folk who lead gullible victims to spend their life's savings on high end equipment that could easily be equaled or bettered by mass market receivers that retail for 1/10 the price, he reluctantly enters the local high end shop.
The sales critter doesn't look like a monster, but then he wouldn't, would he? They say the devil is the master of lies, right? So with fear in his heart our nervous protagonist is led, as a lamb to slaughter, into the Listening Room.
(Cue ominous music in a minor key...perhaps Berlioz's March to the Scaffold...)
But...but...still the salesman doesn't grow horns. Not yet. Maybe he's just waiting until the victim signs on the dotted line, thereby losing his eternal soul.
What's this? Music? Oh, if this be sin, lead me away, Satan! Oh, and listen to the sound between the speakers...why, it's just as if the orchestra is laid out in front of you, just the way it is in the concert hall.
An hour passes and Neophyte hears things he never heard before.
"Wait!" cries a voice from offstage. (This being his conscience speaking.) "Don't reach for your wallet! Leave, and do it quickly before the wily salesman ensnares you any more deeply in his web of lies and deceit!"
Suddenly feigning a remembered chore he'd yet to do, our hero extricates himself from what would surely have become a compromising situation. He reaches his car, panting in fear. Whew! That was close! He nearly fell for it and in doing so would have begun a life of misery, spiraling into ever-increasing debt as he fed his insatiable addiction to High End Audio. For, As Everyone Knows, it's a one-way path to damnation. One dollar...one penny spent on High End, and your soul is forfeit, property of, well, ahem, Him.
Gasping, he rubs his damp, sweaty palms on his pants legs, feeling as though the salesman's handshake has contaminated his very skin. Nothing will do but to get home as soon as possible, there to take a stinging hot shower while chastising his body with harsh, abrasive kitchen cleansers to punish it for being so weak as to succumb to the blandishments of the Master of Lies.
But even after his ritual shower, Neophyte still doesn't feel clean. His very mind has been infected with impure thoughts. It's as though he can still hear the silky highs and transparent midrange...oh, and the low end extension...and...
Aaargh!
Call the exorcist!
With trembling fingers, he dials the number of his True Friend. The only one he trusts to speak the calming words of Reason. The one who will banish the false words of the salesman with Science.
It takes an hour, nay, two, but our hero is once again put upon the path of righteousness, purged of unworthy thoughts.
The next day, he again approaches the salesman in his lair, but this time he is armored with Knowledge and Truth. He accosts the salesman for speaking cleverly crafted lies. He tells him that those instruments weren't really between the speakers. There was nothing there but air.
To which the salesman gives a him a perplexed look and says of course not, it's called imaging.
Our hero pounces! There's no such thing as imaging! It's never been proven by Science! Therefore it doesn't exist!
Taken aback by the vehemence of Neophyte's attack, the salesman responds that imaging is just an illusion produced by--
He's not even allowed to finish his sentence, as Neophyte screams, "Ah ha! So you admit that it's an illusion! And that's tantamount to admitting that it's a lie. And that means that you lied to me!"
With that, Neophyte storms off, never to return. For he is a virtuous man, armed with Science, and he will never fall for illusions or false words.
But he'll never hear music rendered as beautifully, either.
A pity, that, but at least he kept his virtue.
Grey
P.S.: For an amusing--to me, if to no one else--real world example of a rabid Measurements-Are-Everything maven having to eat his words, I refer you to Doug Self's book on amplifiers. Yes, that Doug Self. For whatever reason, he felt compelled to spend an entire chapter of his book excoriating those who dare suggest that there are things you can hear, but not prove. But in the edition I read, he then rather shame-facedly had to admit, grudgingly, that, well, golly, uh, well, you know they...well, dash it all, they went and proved that people could actually hear absolute phase. (Apparently he had singled that out in a previous edition as an example of the damned-fool things that gullible people would fall for.) And he then proceeded to eat very public crow.
But, honestly, wouldn't it have been smarter not to waste an entire chapter mocking those who listen? It would have saved him having to apologize. Better still, would it have been so bloody hard to just shut the hell up, go into his listening room, reverse the confounded leads on the speaker cables, sit down and listen?
For him, apparently so.
But, lo, he paid a heavy price for his arrogance.
Having heard horror tales about 'mind control' and sales folk who lead gullible victims to spend their life's savings on high end equipment that could easily be equaled or bettered by mass market receivers that retail for 1/10 the price, he reluctantly enters the local high end shop.
The sales critter doesn't look like a monster, but then he wouldn't, would he? They say the devil is the master of lies, right? So with fear in his heart our nervous protagonist is led, as a lamb to slaughter, into the Listening Room.
(Cue ominous music in a minor key...perhaps Berlioz's March to the Scaffold...)
But...but...still the salesman doesn't grow horns. Not yet. Maybe he's just waiting until the victim signs on the dotted line, thereby losing his eternal soul.
What's this? Music? Oh, if this be sin, lead me away, Satan! Oh, and listen to the sound between the speakers...why, it's just as if the orchestra is laid out in front of you, just the way it is in the concert hall.
An hour passes and Neophyte hears things he never heard before.
"Wait!" cries a voice from offstage. (This being his conscience speaking.) "Don't reach for your wallet! Leave, and do it quickly before the wily salesman ensnares you any more deeply in his web of lies and deceit!"
Suddenly feigning a remembered chore he'd yet to do, our hero extricates himself from what would surely have become a compromising situation. He reaches his car, panting in fear. Whew! That was close! He nearly fell for it and in doing so would have begun a life of misery, spiraling into ever-increasing debt as he fed his insatiable addiction to High End Audio. For, As Everyone Knows, it's a one-way path to damnation. One dollar...one penny spent on High End, and your soul is forfeit, property of, well, ahem, Him.
Gasping, he rubs his damp, sweaty palms on his pants legs, feeling as though the salesman's handshake has contaminated his very skin. Nothing will do but to get home as soon as possible, there to take a stinging hot shower while chastising his body with harsh, abrasive kitchen cleansers to punish it for being so weak as to succumb to the blandishments of the Master of Lies.
But even after his ritual shower, Neophyte still doesn't feel clean. His very mind has been infected with impure thoughts. It's as though he can still hear the silky highs and transparent midrange...oh, and the low end extension...and...
Aaargh!
Call the exorcist!
With trembling fingers, he dials the number of his True Friend. The only one he trusts to speak the calming words of Reason. The one who will banish the false words of the salesman with Science.
It takes an hour, nay, two, but our hero is once again put upon the path of righteousness, purged of unworthy thoughts.
The next day, he again approaches the salesman in his lair, but this time he is armored with Knowledge and Truth. He accosts the salesman for speaking cleverly crafted lies. He tells him that those instruments weren't really between the speakers. There was nothing there but air.
To which the salesman gives a him a perplexed look and says of course not, it's called imaging.
Our hero pounces! There's no such thing as imaging! It's never been proven by Science! Therefore it doesn't exist!
Taken aback by the vehemence of Neophyte's attack, the salesman responds that imaging is just an illusion produced by--
He's not even allowed to finish his sentence, as Neophyte screams, "Ah ha! So you admit that it's an illusion! And that's tantamount to admitting that it's a lie. And that means that you lied to me!"
With that, Neophyte storms off, never to return. For he is a virtuous man, armed with Science, and he will never fall for illusions or false words.
But he'll never hear music rendered as beautifully, either.
A pity, that, but at least he kept his virtue.
Grey
P.S.: For an amusing--to me, if to no one else--real world example of a rabid Measurements-Are-Everything maven having to eat his words, I refer you to Doug Self's book on amplifiers. Yes, that Doug Self. For whatever reason, he felt compelled to spend an entire chapter of his book excoriating those who dare suggest that there are things you can hear, but not prove. But in the edition I read, he then rather shame-facedly had to admit, grudgingly, that, well, golly, uh, well, you know they...well, dash it all, they went and proved that people could actually hear absolute phase. (Apparently he had singled that out in a previous edition as an example of the damned-fool things that gullible people would fall for.) And he then proceeded to eat very public crow.
But, honestly, wouldn't it have been smarter not to waste an entire chapter mocking those who listen? It would have saved him having to apologize. Better still, would it have been so bloody hard to just shut the hell up, go into his listening room, reverse the confounded leads on the speaker cables, sit down and listen?
For him, apparently so.
But, lo, he paid a heavy price for his arrogance.
SY said:
Are any readers here familiar with the late Professor William B. Wadsworth (1915–1993). Here's a link about him and his lab:
http://scitation.aip.org/getabs/ser...00095000005002914000001&idtype=cvips&gifs=yes
I studied Audio Engineering under Professor Wadsworth, and did project work involving T&S type analysis of transmission line speakers. He was generous enough to spend a lot of time tutoring me one on one since the project work required much more than was covered in his class.
I ask because a few of our conversations did involve amplifier design and TIM.
Pete B.
PMA, have you tried your servo in simulation? Does it control BOTH common mode and differential mode? Your output should be 0,0 with an uneven input offset.
PMA said:
Wow. That looks pretty scary to me. There are a lot of things that would be affected by connecting the servo outputs to the junction of R1 and R2. Why not connect them to the junction of R15 and R16 instead of letting them go to ground? (Assuming the polarity is correct, I didn't check for that.) That's a *much* less invasive point to send the correction voltage to -- there's nothing there but DC anyway. The original connection mixes the correction voltage in with the signal voltage. Kind of makes my skin crawl just to think of it....
Well, that was the solution I came up with 15 years ago when I designed the all MOSFET V-3 amplifier. (It wasn't actually a servo, but rather DC feedback.) I've posted a schematic of that before here at diyAudio, which can be found with the Search function.
I don't think I stole it from you, but who knows? Many of my best tricks were stolen from you, starting with the complementary differential JFET input. (I even stole some good tricks from Andy_C, believe it or not!)
But that's OK -- I've given you back a few good tricks, too. Including one that I know you think is a bad idea, but is actually a good one....
I don't think I stole it from you, but who knows? Many of my best tricks were stolen from you, starting with the complementary differential JFET input. (I even stole some good tricks from Andy_C, believe it or not!)
But that's OK -- I've given you back a few good tricks, too. Including one that I know you think is a bad idea, but is actually a good one....
john curl said:
Charles Hansen said:
John - yes, I simulated the circuit - as you can see the image was a result of MC.
Charles - for just DC zero at the output, your solution works better. For AC, there is more invasion if servo output connected between R15 and R16 (even frequency response is more influenced). The servo moves voltage potential of this junction ANYWHERE.
PMA said:
Sorry, Pavel, I am not understanding what you are saying. I think it is just the language barrier. Could you re-state this in another way? Thank you.
To get back to the AD844... now that we all know what Pins 1 & 8 are for - how about Pin 5?
I have asked ADI about this and gotten no answer. Otherwise, the 844 seems pretty much a spec similar superfast current mode opamp with no big obvious differences from an AD811, except for the Pin 5 connection as an output - or is it an input?
I use it for some tricky things, as does (I suspect) Charles, but does anyone know what was it's original purpose? Scott?
Regards, Allen
I have asked ADI about this and gotten no answer. Otherwise, the 844 seems pretty much a spec similar superfast current mode opamp with no big obvious differences from an AD811, except for the Pin 5 connection as an output - or is it an input?
I use it for some tricky things, as does (I suspect) Charles, but does anyone know what was it's original purpose? Scott?
Regards, Allen
Allen Wright said:
I don't know the original purpose - possibly custom compensation? But I use it for both input and output, sometimes at the same time. Or as a summing point to sum an external signal current and the current resulting from the regular input signal. This is a very versatile chip.
If I may bring up another issue: a few posts earlier we found that the AD844 buffer has the bulk of the supply current as bias current - some 6mA. That means it can deliver up to 12mA peak in class-A, which is 8.5V RMS in 1k and even about 5V RMS in 600 ohms. Clearly, trying to put this output stage in class-A with a current source loading of a couple of mA seems irrelevant.
Are people looking at that when they decide to use - or not - class-A output stage biasing? I quickly checked the OPA637: 7.5mA; the OPA 2137 has only a fraction of a mA so might benefit from class-A output stage biasing. What is the sort of general rule people use for this?
Edit: Scott's 797 has a supply current of 10.5mA.
Jan Didden
Ad844
You guys simply do not read datasheets (or is it just easier to ask here? 😀 )
----
A current applied to the inverting input is transferred to a complementary pair of unity-gain current mirrors that deliver the same current to an internal node (Pin 5) at which the full output voltage is generated. The unity-gain complementary voltage follower then buffers this voltage and provides the load driving power. This buffer is designed to drive low impedance loads, such as terminated cables, and can deliver ±50 mA into a 50 Ω load while maintaining low distortion, even when operating at supply voltages of only ± 6 V.
------
and -
Figure 7. Feed Forward Network for Large
Capacitive Loads
i.e. pin 5 used for this.
You guys simply do not read datasheets (or is it just easier to ask here? 😀 )
----
A current applied to the inverting input is transferred to a complementary pair of unity-gain current mirrors that deliver the same current to an internal node (Pin 5) at which the full output voltage is generated. The unity-gain complementary voltage follower then buffers this voltage and provides the load driving power. This buffer is designed to drive low impedance loads, such as terminated cables, and can deliver ±50 mA into a 50 Ω load while maintaining low distortion, even when operating at supply voltages of only ± 6 V.
------
and -
Figure 7. Feed Forward Network for Large
Capacitive Loads
i.e. pin 5 used for this.
Re: Ad844
Pavel, I think the question was why this point is brought to an external pin. It is the only CFA that I know (from ADI) that has this brought out. Since bringing it out increases the parasitic capacity at Tz, which decreases the bandwidth, there must be a good reason why it it done anyway.
Jan Didden
PMA said:
Pavel, I think the question was why this point is brought to an external pin. It is the only CFA that I know (from ADI) that has this brought out. Since bringing it out increases the parasitic capacity at Tz, which decreases the bandwidth, there must be a good reason why it it done anyway.
Jan Didden
Jan,
IMHO there is an answer from the datasheet (already mentioned) - feedforward compensation pin for large capacitive loads.
IMHO there is an answer from the datasheet (already mentioned) - feedforward compensation pin for large capacitive loads.
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