| PanzerLord |
The caracteristic sound of an amplifier (or CD player for that matter), is based on the harmonic distortion. The statement that there is a transistor with "good sound" is both true and false, actually 99% false.
The human ear percepts third harmonc distortion as a "foul" sound, the second harmonic however makes the amplifier sound "warm". Tube amplifiers have very large second harmonic distortion (often1-10%), thats`why they have a "warm and soft" sound.
You could go the effort and tracking down transistors that are expensive, and are used in Krell, Electrocomaniet and so on, but the results will be minute.
There are many more and better ways to make your amp sound
the way you like, just remember that third (odd harmonics generally) has an ugly and harsh sound.
You could with a little effort design an amplifier in the 0.001% THD region with general purpose transistors (BC546, BD139, TIP35), and make it sound like a million!!
The key is using good constant current source and an active mirror load at the differential input (if you want a warmer sounding amplifier, just replace the current mirror with resistors, this will increase the second harmonics).
OK, a lot of talk here...the bottom line is, its the circuit topology that desides the THD and S/N. I a wilson current source would make a differental input pair consisting of BC546/BC556 transistors sound far better than replasinbg the wilson with a Transistor-diode current source and using 2SC2240 transistors (however I would use the 2SC2240/2SA970 anyway because they have higher Vce tolerances, and they have higher beta (a wilson curren source with that also uses these, will have an output impedance in the 10-50Mohm region). |
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| Solid Snake |
Yep that sounds right. Even so, you shouldn't be able to tell the difference between a good tube and good SS amplifier if the distortion is low enough. It's also true that most of the sound comes from the circuit around the transistors. I use TIP35/TIP36 in almost all of my amps. They'll sound as good as I make them sound, and recently I've been able to make them sound very very good. Also because they're included in the feedback loop, I can pull a TIP35, replace it with a TIP41, TIP31 or 2N3055 and there's no difference in sound (power handling excluded). It's mostly in the circuit, garbage in means garbage out. Transistors that work in the 50Mhz range aren't going to give you any advantage if your circuit sounds like **** at 1Khz.
By the way, what exactly is a current/active mirror? |
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| sss |
whats a wilson current source ?
what do u think of using chip based current source in the lpt? |
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| PMA |
| The sound often called as a "transistor sound" often results (according to my experience) from intermodulations of audio signal with RF interference or D/A residuals at CD output, even if they are very low in magnitude. This occurs also in case you build an amp with THD as low as 0.0005% with only 2nd harmonic line in the spectrum. I have made a lot of experiments with this phenomenon, amps with absolutely same THD and IMD specs (hardly measurable) did sound quite different according to HF residuals filtration. Also - the signal transfer on higher current level (50 Ohm load) brings great improvement to sound quality (grain disappears, bass is tough, midrange and treble clear and localization improved). Bruce Candy must have found the same, as Halcro dm58/68 use also 50 Ohm inputs and current inputs in addition to standard 50k inputs. |
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| EternaLightWith |
What do you mean by HF residuals filtration?
P.S. Any documentation of this phenomenon?
DAvid |
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| john curl |
You folks are thinking about the problem, but you are not thinking it through. First of all, 3'rd harmonic is actually almost as acceptable as 2'nd harmonic. How do we know? Because 3'rd harmonic is the only distortion normally measurable on analog magnetic tape, and its value is usually between .1% and 10% depending on output level. How is it that we can, or could listen to analog tapes without crying out in pain?
It is the HIGHER ORDER ODD HARMONICS that are the big problem. For example, 7th and 9th harmonic. 8th harmonic should be OK, within reason.
Transistors generate much more higher order distortion than do tubes. This is because of the curvature of their transfer function, due to very nonlinear Gm. Tubes also have some nonlinearity in gain, but they work on a different principle and change less over current, and usually have less distortion, and it will be of lower order in general. |
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| fdegrove |
Hi,
| quote: | | The human ear percepts third harmonc distortion as a "foul" sound, the second harmonic however makes the amplifier sound "warm". Tube amplifiers have very large second harmonic distortion (often1-10%), thats`why they have a "warm and soft" sound. |
If you'd replace the words "third harmonic" distortion with odd order harmonic distortion I'd agree with the above.
Tube amplifiers do not have large amounts of "second", let's call that even order, harmonic distortion per se. Those that do present such a harmonic distortion will tend to sound unrealistically warm and rich and will be called by a lot of people of having a "tube" sound.
While I do appreciate what tubes do right, I do refuse to accept that there is a "tube" sound as such.
Naturally tubes and semiconductors distort in a different way when overloaded, sent into clipping and alot of this characteristic behaviour has led to the believe that a tube amp seems much more powerful than its' equivalent semi-conductor amp.
In reality it's just the clipping behaviour of the tube amp that when sent into clipping produces more even order harmonic distortion which the human ear perceives as more related to the signal than distortion containing predominantly odd harmonics.
When clipping occurs with semi-conductor amplifiers it occurs much more abruptly and subjectively seems as if the amp has ran out of steam and distorts in a horrible manner. (Odd order harmonic distortion)
Which ever one prefers, it's still distortion nonetheless.
Cheers,;) |
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| Richard C |
Surely everything we perceive as 'sound' is distorted. If musical instruments didn't add harmonic distortion they would all sound the same. Air has a non-linear transfer characteristic, our ears aren't linear and neither is the way our brains process 'sound'.
Suddenly amplifier distortion doesn't seem so bad. |
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| fdegrove |
Hi,
| quote: | | If musical instruments didn't add harmonic distortion they would all sound the same. |
That's the signal you use as your source which is your reference.
If you have an amplifier that adds tons of even order harmonics to a signal that is mainly odd order harmonic in overtone I'm afraid you can kiss the term High-Fidelity goodbye.
Cheers,;) |
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| PanzerLord |
I both agree and disagree on that one, but I still insist on the odd (and especially the third) harmonics being much more unpleasant than the 2nd. I`ve read a couple of textbooks that also agrees on my opinion... But could of course be wrong, since I haven`t really got great experience on this, nevertheless, I know how to decrease harmonic distortion in amplifiers, and I`m pretty good at it. And that`s a start!;)
Tube generally have much more harmonic distortion than semi`s, because they have an much more unlinear transfer curve. I`m pretty sure everyone agrees on that....
Again, the distortion in transistorts depends much much more on the topology, and how the input and output impedances "harmonize" with eachother (for instance, in the output transistors, it`s very important to have the input capacitance in mind, which also determines the input impedance for various frequencies). I don`t know if that came out the way I meant it, it sounded very good in norwegian...;)
Regardless, everyone must agree on, that distortion should be as low as possible around 3kHz, it`s around this area that the human ear is most sensitive. The key is to design the amplifier to have a P1 point above above 1kHz, it`s impossoble to have a harmonic distortion carachteristic that is a straight line through the audio spectrum. No matter what we do, the distortion will rise with higher frequenzy above the P-point. |
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| fdegrove |
Hi,
| quote: | | Tube generally have much more harmonic distortion than semi`s, because they have an much more unlinear transfer curve. I`m pretty sure everyone agrees on that.... |
Huh? No, I do not agree at all.
Cheers,;) |
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| PanzerLord |
What`s the source of the higher THD tube amplifiers then?
I really want to know, since the sources of my knowledge around tubes generally are schoolbooks and amplifier construction manuals...
I`ll quote G. Randy Slone:
"There are a variety of reasons that many audiophiles prefer vacuum tube audio power amplifiers to solid state designs. The most probable reason is that tube amplifier naturally produce (again, see transfer curve) a relatively high percentage of second-order harmonic distortion. In musical terms, a secon order harmonic is always one octave above the fundamental frequency, so the tones can never become dissonant with the program material. The sonic effect of adding second order distortion is similar to hearing two musical tones instead of one, simulating a perception of body or character to the original program material."
I have over 9 yars of experience in electronics, and I can`t honestly remember once, anyone or any textbook claiming otherwise....:)
My goal here isn`t to provoke you tupe-lovers, I think this subject is extremely interesting, and I really enjoy discussing these things:). It makes me seeing things a little bit in perspective.. |
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| Christer |
| quote: | Originally posted by Richard C
Surely everything we perceive as 'sound' is distorted. If musical instruments didn't add harmonic distortion they would all sound the same. Air has a non-linear transfer characteristic, our ears aren't linear and neither is the way our brains process 'sound'.
Suddenly amplifier distortion doesn't seem so bad. |
Hm, I am not so sure I would say that instruments cause
distorsion. The harmonic spectrum of them is inherent to them
and is desirable, since we seem to enjoy intrumets sounding
different. As for the distorsion in air and the ear,
this is always present, whether we listen to real life
sound, speach, music, cars etc. or audio equipment, so I would
guess our brain has
learnt to compensate rather well for these forms of distorsion.
Distorision in audio equipment, on the other hand is a very
new phenomenon, and we have had only about a century
to try adopting to that (evolution is slow in humans). Besides, since the various equipment sound different, we don't get a fair chance to adopt to it.
For instance, im a disturbed by the sound of cars, I have a big
parking lot outside my kitchen window, but at least they sound
as I am used to, not distorted by audio equipment. Two floors
above me there is a man playing the grand piano, but apart
from him being a rather good musician and play music I can
stand or even like, I clearly hear, despite two concrete floors
in between, that it is the sound of a real instrument, sounding
if not quite like in a concert hall, so at least normal. On the other
hand, the neighbours one floor above me obviously has a
very crappy audio equipment, probably a cheap home theater
setup, and it is very disturning since it sounds so very wrong
and confuses my brain. |
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| fdegrove |
Hi,
| quote: | | What`s the source of the higher THD tube amplifiers then? |
Remove all feedback on a semi design, local, nested global and what have you and you'll see what figures you'll get.
One thing you can't remove is the inherent feedback of a triode.
Cheers,;) |
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| Christer |
| quote: | Originally posted by PanzerLord
Tube generally have much more harmonic distortion than semi`s, because they have an much more unlinear transfer curve. I`m pretty sure everyone agrees on that....
|
I used to believe so too, thinking that the tube hype is only
about people wanting a particular manufactired sound. After
readin a post by Torsten/Kuei at Audioasylum I am not so
sure anymore. I know next to nothing about tubes. However,
as I recall, his claim was that he only approved of certain
types of tubes and only when used in certain ways, and in
these cases they had an almost perfect linear transfer
characteristic. I don't know if it is true, but it made me rethink
that maybe there is something to this tube stuff after all. |
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| mrfeedback |
| quote: | Originally posted by fdegrove
While I do appreciate what tubes do right, I do refuse to accept that there is a "tube" sound as such.
Naturally tubes and semiconductors distort in a different way when overloaded, sent into clipping and alot of this characteristic behaviour has led to the believe that a tube amp seems much more powerful than its' equivalent semi-conductor amp.
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Yes, I have heard two very fine amplifiers from the same stable, one tube and the other transistor.
At levels less than overload, both amplifiers were remarkably similar, and on the short listening session the tube amp came out as being slightly blacker between notes and not much else difference - perhaps slightly 'sweeter' overall.
IOW both amplifiers were musically very good indeed, and just about any listener would be perfectly happy with either one.
Yes, overload behaviour is mission critical and tube amps do not by definition always sound less bad than overloaded transistor amplifiers.
The above mentioned transistor amplifier was designed to incorporate benign overload behaviour and it shows - there are no transient instabilities or rail sticktion (latchup) nasties and the overload sonics of this transistor amplifier are indeed nicely benign and inoffensive - it just quietly alerts the listener to turn down a bit in a similar manner to an overloaded tube amp.
Eric. |
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| azira |
I think it's interesting that so much technical thought goes into reproducing music and how to describe how "good" the reproduction is from the electronics point of view without music being given much of a chance to defend itself.
Here's my two cents then:
Music is played from scales. But those scales were generated FROM the harmonics of a fundamental note (440 Hz - A). Now music theorists consider "good" sounds and consonant and "bad" sounds as dissonant (which if used right can be good...) The most consonant sounds are the octaves and then the harmonics starting from lowest order first that aren't octaves of previously encountered harmonics.
Anyway to put it simply, the 2nd and 4th harmonics are octaves of the fundamental, according to music they should actually reinforce the root note being played (which is a possible reason why the even order clipping distortion of tubes sounds "warm")
The 6th harmonic (still even order,adding to that warm sound) is called a 'fifth'.
What's key is that the 6th harmonic is actually just an octave of the 3rd harmonic. If the 6th adds to the warm sound, the 3rd HAS to as well.
The point is, since harmonic distortion energy tends to be concentrated in the lower harmonics first even order is less likely to contan energy in harmonics that start to be dissonant. But the even vs odd stereotyping really is over generalized.
Why is odd worse than even in the end? Because odd order harmonics will reach dissonant tones faster, but that doesn't make all odd order harmonics "bad"
--
Danny |
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| PMA |
| quote: | Originally posted by john curl
It is the HIGHER ORDER ODD HARMONICS that are the big problem. For example, 7th and 9th harmonic. 8th harmonic should be OK, within reason.
Transistors generate much more higher order distortion than do tubes. This is because of the curvature of their transfer function, due to very nonlinear Gm. Tubes also have some nonlinearity in gain, but they work on a different principle and change less over current, and usually have less distortion, and it will be of lower order in general. |
But tubes do the same. Have a look at tube amps reviewed by Stereophile and you will see that they also do have 8th, 10th harmonics at the spectrum, their spectral response is like ridges and valleys. But what they actually do - they are quite insensitive to HF intermodulations and they mask. Masking is the big trouble. Most of producers do not try to make low distortion components, but they tune the audio chains to mask the problems, not to solve them. Transitor and OpAmp gears are more sensitive to the signal quality and cable phenomena - that's all. Once you solve it you will get to higher league compared to "pleasant sounding" amps. Direct comparison shows that "pleasant sounding" amps bring their own coloration, hide the details, unfocus the soundstage and bring something like "tail" behind the sound, also unable to reproduce "silence" under (between) tones. |
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| Christer |
Azira,
very intersting analysis. I have never thought of that before,
and cannot remeber anybody else making this comparison. It
is probably not easy to draw any straightforwards conclusions
from it, but at least it might indicate the usual "odd is good even
is bad" distinction is way too simplistic, which I suppose most
agree on anyway, but not for the same reasons.
Hm, I just recall PRR recently wrote that musical instruments
tend to have harmonics that are not perfect multiples of the
fundamental but slightly off. If that is true, it complicates the
issue further. |
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| AKSA |
In the immortal words of Mark Twain, who remarked that he'd never met a man he didn't like, I'm tempted to say that I've not read a single post in this thread I didn't agree with.
In point form, here's my take:
1. The musical scale favors chord structures with minimal discord, and this means H2 and H3 and maybe H4 are just fine. But beyond that, we rapidly enter into discordant sounds, precisely because music is played in complex chord structures and harmonics beyond H3 quickly degenerate into discord.
2. Now, music is also about mood - and discord is a part of this manipulation. Rikard Strauss, Rachmaninov, many of the tone poem composers, even Sibelius and the later Beethoven String Quartets, ALL exhibit strong discord from time to time. This music is not everyone's cup of tea, but it is deeply evocative to me, and clearly the discordant balance is very carefully structured.
3. Since music is based around 'pleasing' chord structures, and the ear is so extraordinarily sensitive to so-called 'discord', it follows that intermodulation 'sum and difference' products, which have no musical relationships at all to any tonic scale I know of, will be pivotal in corrupting recorded renditions of performances.
4. Thus, on this basis are identified two separate issues; one harmonic overtones, produced by the non-linear amplification process; and sum/difference intermodulations, which also result of non-linearities in the process, and seem particularly troublesome with time-smear distortions, such as those generated in slow global negative feedback loops. As an aside, some of the amplitude modulated jitter problems in the digital domain create intermodulation products, which are very nasty.
So, our amplification process should keep all harmonic generation low order, with particular emphasis on avoiding H5 and higher, and it should be clean, and as linear as possible, to avoid the blight of 'sum/difference' intermodulations, which typically give a muddy, vague sound. I guess this comes back to the tired old advice we've all heard a million times, 'As linear as possible, and no global feedback'. Of course, this is as practical as riding a beaver across the Sahara, but never mind, we hear it constantly anyway.....
That said, when one listens to a good quality system from afar, and then a genuine musical instrument, like Christer's Grand Piano in the apartment above, the skilled listener can clearly pick up the difference. Why is this, and once we identify it, could this be the key to producing truly realistic sounds?
Of course, to open another can of words, the dreadful truth is that the recording process is probably as guilty of corrupting the music as the playback - and arguably more so.
Cheers,
Hugh |
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| PMA |
| quote: | Originally posted by AKSA
So, our amplification process should keep all harmonic generation low order, with particular emphasis on avoiding H5 and higher, and it should be clean, and as linear as possible, to avoid the blight of 'sum/difference' intermodulations, which typically give a muddy, vague sound.
That said, when one listens to a good quality system from afar, and then a genuine musical instrument, like Christer's Grand Piano in the apartment above, the skilled listener can clearly pick up the difference. Why is this, and once we identify it, could this be the key to producing truly realistic sounds?
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Nice post, Hugh. Indicates that you have passed the way through.
Pavel |
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| Christer |
| quote: | Originally posted by AKSA
2. Now, music is also about mood - and discord is a part of this manipulation. Rikard Strauss, Rachmaninov, many of the tone poem composers, even Sibelius and the later Beethoven String Quartets, ALL exhibit strong discord from time to time. This music is not everyone's cup of tea, but it is deeply evocative to me, and clearly the discordant balance is very carefully structured.
|
Discords are very important in a lot of music as you point out.
However, as I am sure you meant but just didn't emphasize, it
is used deliberatly for dramatic effects by the composers,
similar to juxtaposition of complementary colours in painting etc,
and we do not want our audio equipment to introduce such
effect in places they were not intended by the composer.
The best distorsion spectrum is no distorsion spectrum, but
that is more than we can ask for, of course.
| quote: |
Of course, this is as practical as riding a beaver across the Sahara, ...
|
I'll give you the gold star of the week for that one, Hugh. :)
| quote: |
Of course, to open another can of words, the dreadful truth is that the recording process is probably as guilty of corrupting the music as the playback - and arguably more so.
|
Much more so. Guess why I usually prefer historical recordings,
apart from their usually superior musical qualities. I received a
CD this morning that a friend had posted to me of a modern,
although not from the most recent years, recording of Faurés
Requiem, which he thought was an example of the few modern
recordings that actually sound good. He even seemed to think
it sounded better than Ansermets recording on Decca from 1955
which we both admire. Just did some quick comparisons, but
****, it is decent, but not at all like the old Decca. Where is the
acoustics around the choir and orchestra, why can't I hear
that the choir is actually spread out over the soundstage and
not just located at a single point, why does it sound as if the
choir distors in the fortes? Ok, the Decca also has some distorsion
in the fortes, but there I can still hear what they are singing. |
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| AKSA |
Thank you PMA and Christer!
The star of the week is actually a literary metaphor.
To complete the picture, and see just how grubby and dry my humour is, see Roald Dahl's 'Uncle Oswald', a wonderful story with a captivating twist........:devilr:
Actually, did you know that using a bipolar and a mosfet, it is possible to build a unity gain buffer with an input impedance of 200K and an output impedance of 40 milliohms? Only local feedback, no global. :D
Cheers,
Hugh |
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| PMA |
| Where did you find an inspiration, Hugh? ;) |
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| Audiofanatic |
| quote: | Originally posted by sss
whats a wilson current source ?
what do u think of using chip based current source in the lpt? |
Can someone explain this to me? Or show a schematic?
Thanks!
Audiofanatic ;)
P.S. I like both tube and SS! |
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| Christer |
I think Panzelord just made a typo and meant a Wilson current
mirror, not a current source. Now, don't ask me what that is,
I always mix up Wilson and Widlar current mirrors, and only
remember what one of them looks like, not knowing which of them
it is. |
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| Christer |
| Hugh, I love that type of humour. Keep it up, please. |
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| fdegrove |
Hi,
| quote: | | Now, don't ask me what that is, I always mix up Wilson and Widlar current mirrors, and only remember what one of them looks like, not knowing which of them it is. |
A quick refreshment on current sources:
BJT CURRENT MIRRORS
Cheers,;) |
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| Audiofanatic |
Mil gracias hermano!
Thats what I call humor!
Thanks again Frank!
Audiofanatic ;) |
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| PanzerLord |
Sorry about the confusion, it`s wilson current MIRROR, and wildar current SOURCE. My mistake, I`m mixing them too...
Ref.:
-Micrelectronic circuits 4th ed." by Sedra/Smith
-"Analoge kretser og komponenter" (analouge circuits and compnents) by Rolf Ingebrigtsen
When we desire a current source I<10uA, wildar is perfect, output impedance >10Mohms. (these values are very ca. and are solely dependent on beta and Va
A modified wilson has output impedance >1Mohm`s (assuming high-beta BJT`s). An ideal current source has infinite output impedance, this is specially important in the input stage (differental amp).
Higher output impedance in the current source means higher CMRR and PSRR, and greater linearity, combined with an active load (current mirror), the preformance is second to none -whatsoever!!!
Compared to the "shcoolbook" design of the diff. amp with resistors (and even the transistor-diode current source) the difference is 1/100-1/1000 and often more)!!
Regardless, there are people claiming otherwise, but that`s wrong, you can`t cheat on physics!! |
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| PanzerLord |
| These are the three types of current sources I use, it`s crucial the beta-match the bjt`s in the modified wilson!!! |
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| Audiofanatic |
Hi PanzerLord,
Thanks for the pic.
The seccond one is the one I'm using(without Q5) but didn't know the name of it.
I'll mod it and will report later.
Thanks again!
Audiofanatic ;) |
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| PanzerLord |
-Your case (without Q5) output resistance is ro=Va/Ic
-My case (with Q5) The output resistance for the wilson is Rout=beta*ro/2
=beta*(Va/Ic)2
Assume a Va=100V, and Ic=1mA and beta=200:
-Your case:
Rout=100V/1mA=100kohm.
-My case
Rout=200*(100V/1mA)/2=10Mohm.
I can assure you that preformance will be improved! (CMRR will in theory be doubled) |
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| Audiofanatic |
| quote: | Originally posted by PanzerLord
-Your case (without Q5) output resistance is ro=Va/Ic
-My case (with Q5) The output resistance for the wilson is Rout=beta*ro/2
=beta*(Va/Ic)2
Assume a Va=100V, and Ic=1mA and beta=200:
-Your case:
Rout=100V/1mA=100kohm.
-My case
Rout=200*(100V/1mA)/2=10Mohm.
I can assure you that preformance will be improved! (CMRR will in theory be doubled) |
THANK YOU!
Audiofanatic ;) |
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| PanzerLord |
| This is the output distortion onmy 50W class A (see thread under solid state topic) with wilson current mirrors as current sources: |
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| PanzerLord |
I have now replaced the modified wilson current mirror with a standard current mirror (two BJT`s ).
If I have replaced the active load (a standard wilson current mirror) on the input diff. amp. on both cases, the difference would have been far more noticable... |
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| PanzerLord |
| quote: | | The seccond one is the one I'm using(without Q5) but didn't know the name of it. |
.
A standard current mirror Rout=ro=VA/Ic |
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| Solid Snake |
| I think I am completely missing the point of these circuits. |
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| Christer |
Since some confusion seem to still be around, and I found out
what confused me, maybe it can help somebody else.
As is well known, a current mirror can be used as a current
source by tying a CCS to (or elsewise draw a constant current
from) one half of the mirror. The other half will then replicate
this current source, more or less perfectly depending on the
mirror topology etc. When Panzerlord referred to a Wilson
CCS he actually meant a Wilson current mirror used as a CCS
in the way described above. I just had never heard the term
Wilson CCS before, but the concept is well known, of course.
Then is the question what is won by this since the constant
current to be replicated seems not generated by a CCS in
his case but by an RC net, but his simulations seem to
indicate advantages. |
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| AKSA |
Yes, good point.
You can also use the Wilson Current Mirror as a current multiplier by configuring non-symmetrical emitter degeneration. I have seen this done with triodes to effect impedance transformation without a transformer. VERY cool!!
However, I've done a lot of work on current mirrors, which are yet another elegant engineering solution to a problem which scarcely exists. The problem is that they are an active load, and this introduces more non-ohmic behavior into the mix at the point where the diff pair drives the voltage amplifier. I have shown mathematically, some year or two ago now on this forum, that even with a perfect current mirror, the single ended take off drives the diff pair into asymmetry; precisely what we don't want. I have found that PP SS amplifiers sound better without them.
Cheers,
Hugh |
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| Ola |
In the middle of the 80's there was an article in HiFi News and Stereo Review about harsh transistor sound. The problem there was about japanese mass-production amps versus hifi stuff from smaller companies.
Author did a series of listening sessions with different amps and listenes and found 100% correlation between a harsh sound and the level of measured radio frequencies at amp's output. He wrote that tubes and the ways they are used in amps are by themselves less suspective to passing radio frequencies through. |
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| PMA |
| quote: | Originally posted by Ola
In the middle of the 80's there was an article in HiFi News and Stereo Review about harsh transistor sound. The problem there was about japanese mass-production amps versus hifi stuff from smaller companies.
Author did a series of listening sessions with different amps and listenes and found 100% correlation between a harsh sound and the level of measured radio frequencies at amp's output. He wrote that tubes and the ways they are used in amps are by themselves less suspective to passing radio frequencies through. |
Correct. The same problem is with CD players. D/A residuals must be supressed. Preamp is to be designed the way it is not affected by RF and D/A residuals.
For the same reason, signal transfer on high current level (50 Ohm load) gives much better results compared to standard solutions (voltage output with 100 Ohm - 1kOhm output impedance followed by middle impedance input like 10k - 100k). |
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| millwood |
| quote: | Originally posted by Ola
Author did a series of listening sessions with different amps and listenes and found 100% correlation between a harsh sound and the level of measured radio frequencies at amp's output. He wrote that tubes and the ways they are used in amps are by themselves less suspective to passing radio frequencies through. |
did the author see if the results would change if RF noise was eliminated from the Japanese amps? would they sound still as harsh?
The foundamental flaw in the methodology is that the author used a correlation to imply causation (?). If I ran a regression on a nation's GDP on its cumulative rainfall, the correlation would be very high but it would be crazy for me to claim that rainfalls drove GDP thus we should have more rainfall for higher GDP. |
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| PMA |
| quote: | Originally posted by millwood
did the author see if the results would change if RF noise was eliminated from the Japanese amps? would they sound still as harsh?
The foundamental flaw in the methodology is that the author used a correlation to imply causation (?). If I ran a regression on a nation's GDP on its cumulative rainfall, the correlation would be very high but it would be crazy for me to claim that rainfalls drove GDP thus we should have more rainfall for higher GDP. |
OK. I have done a great number of listenning tests with a couple of people. The same circuit, THD at 1kHz below 0.001%, IMD of the same order. The only difference was HF filtration. Quite different sound, without any doubt. Harsh and grain affected. The same for signal transfer by higher current (50 Ohm output impedance, cable and 50 Ohm load impedance). All of those theoretical disputes about 13th and 17th harmonics are simply out of the target. |
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| Ola |
| quote: | | The foundamental flaw in the methodology is that the author used a correlation to imply causation (?). If I ran a regression on a nation's GDP on its cumulative rainfall, the correlation would be very high but it would be crazy for me to claim that rainfalls drove GDP thus we should have more rainfall for higher GDP. |
There was a lot of schematics analysis in this article and pictures of scope screen, showing in what stage and how much and radio frequency was present. Don't consider other people being stoopid. |
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| millwood |
| quote: | Originally posted by Ola
There was a lot of schematics analysis in this article and pictures of scope screen, showing in what stage and how much and radio frequency was present. Don't consider other people being stoopid. |
I would never consider anyone stoopid.
Having said that, the foundamental flaw there is that the auditor didn't explore the sound when there is NO RF signal/distortion in the amp.
Just because two things showed up at the same time doesn't mean there is a cause-and-result type relationship, no matter how many scope pictures taken and analysis done.
You disagree? |
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| Ola |
| Well, I understand that You have not read that thing, but dear to say it was fundamentally flawed. |
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| john curl |
| Panzerlord, I used the first example in an ultra low distortion 600 ohm driver that I designed for Sound Technology to have max performance up to 100KHz. Worked for me, and they used it in their next generation THD analyzer. |
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| millwood |
| quote: | Originally posted by Ola
Well, I understand that You have not read that thing, but dear to say it was fundamentally flawed. |
my conclusion is based on your description of that article. I assumed you did a good job there. |
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| john curl |
Ola, I think you have a point.
There is a big difference between amplifier bandwidth and high frequency amplifier performance (slew rate, non-linear capacitance, xover distortion, etc). Amplifier bandwidth is usually determined by the amount of negative feedback available. With tubes, this is usually limited by the LOW FREQUENCY oscillation called 'motorboating', not just by high frequency techniques. This usually limits the max feedback in the tube amps to about 20dB.
With IC's and discrete power amps, you can have 80+ dB of feedback, because you can direct couple the stages and have no low frequency problems. Also, you can avoid transformers in the output stage. This gives you bandwidth, but not necessarily better performance at high frequencies.
When you put RF into a tube amp, you should just get a rolloff in level, without slew rate limiting. However, with a solid state power amp, you will usually get slew rate limiting somewhere, or else you have deliberately rolled off the high frequencies at the input. This is an important difference between normal tube designs, and NORMAL solid state designs |
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| PanzerLord |
I use both 1 and 2. In my 50W class A design (only simulation yet), the 1. as an active load, and 2. as a current source. The distortion preformance made my jaws drop, litterally, I tossed away those lousy resistors at once! (I`ve done simulation on a previous amp that I buildt, and the simulation resemebled the preformance in the real one...spending time in front of the simulator pays off, but doesn`t do you any good if you f.ex.connect the - to speaker directly to the ground plane on the amp-PCB, i.e. close to the small-current ground).
The - to speaker should of course connect to the HQ-point |
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| john curl |
| Please take care, I have found that simple is usually better, unless complication can make a better throughpath. Sometimes it does, sometimes it doesn't. Even though I found the type 1 impressive, I was working with one frequency at a time, as this was for a piece of test equipment. Generally, I personally I would avoid the complication for my own audio designs. |
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| PanzerLord |
| quote: | | lease take care, I have found that simple is usually better, unless complication can make a better throughpath. |
I`ve used standard amp stages all the way, and a simple (and very often used) global NFB network. The only "complicated " elements in my design is the active load (standard wilson current mirror), and the current sources (which need to have the highest Rout as possible).
These are simple but powerful improvements that both increases bandwith and linearity, they seem complicated beacuse there are active components involved, but f.ex. calculations would actually been more complicated withot these improvements.
I only decided what bias currents that should pass through the respective stages, plus the 2-pole CC feedback.
Ok, had to think of the input and output impedances (and capacitances) for each stage also, but that wasn`t a great issue since the circuit topology I used eliminated that problem...
Though, I would like to say, I was a bit sceptic with the wilson current wirror as an active load, the output resistance went to the roof. But the simulator showed much improvement in both distortion and stability, especially stability, due to the increased bandwith...
I`m still doing some calculations around the input resistance of the buffer stage. |
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| PanzerLord |
After looking at it for a while, and comparing simulations with what I expect in the real world, I`ve come to the conclution that Iref (in any current mirror acting as a current source) depends (to a certain degree) upon the voltage over the resistors (hence the capacitor for filtering). The PSRR for this current source is acceptable for a regulated power supply, but for unregulated with ripple could (possibly, but not likely, I actually doubt it) be another situation....
I`ve designed a modified current source which consists of a JFET current source, and the modified wilson current mirror(which is 100% undependent of the supply voltage).
At lower railvoltage, the JFET current source source could be a stand-alone.
But with railvoltages with over +-30V it`s impossible to use the
JFET source alone, most JFET`s avaliable have a Vds,max around 30V, the largest Vds I`ve seen is 60V...now that could become a problem.
Thats why I designed this circuit, you could easily use a 20V JFET, and high voltage beta-matched BJT`s, with no loss in preformance compared to the JFET current source alone. The wilson current mirror replicates Iref 100% (and Iref is 100% undependent of rail voltage), and operates at the Vce,max of the BJT`s).
I thought this wouldn`t improve the (simulated!) distortion preformance in my 50W amp project since the powersupply is defined as batteries in the simulator. But the distortion at higher frequencies where actually improved in unbalanced mode, and in balanced mode the improvement was through the whole spectre (20Hz-20kHZ)! |
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| john curl |
| Schematic is wrong. |
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| PanzerLord |
Nope, this configuration is used in some op-amps (a simplified , and a bit different version in f.ex. 741, not with JFET). The JFET current source is something I have seen before (I actually found it yeasterday in an old schoolbook lying around).
And I wonder why I haven`t thought of this before, the JFET gives a 100% stable Iref at all times and is totally independent of variations in the supply voltage, and the wilson mirror gives a 100% excact copy of Iref.
There is nothing wrong about this schematic, I`ve done a lot of simulations with this circuit in the last hours, and it`s working perfectly. The tail current in my input stage is rock stable, to say the least.
I`m going to do a lab with this one in a couple of days, I`ll let you know....I really don`t understand why you think this schematic is wrong, I`m 150% certain that you have misunderstood something, because I`m 150% certain that this works. Calculation, simulation and common sense tells me that! |
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| andy_c |
Hi,
Shouldn't R2 be in the source of Q1 instead of the gate? It looks like the IDSS of Q1 is about 80mA according to the Philips data sheet of the J108. Since your current meter shows around 5mA, I'm assuming you may have transcribed the schematic, inadvertently moving R2?
Also, since Q4 and Q6 are not part of a matched pair, I think it would be a good idea to have small emitter resistors to help equalize the currents. I've played around with current mirrors in simulation by having transistor models that are identical except for tweaking Is for a 10-20% variation between devices (making the current ratio approximately the same as the ratio of Is values in the absence of emitter degeneration). I don't think individual discrete devices track well enough to be able to get away without them. Just a thought, not meaning to nitpick here.
Another thought - have you seen the Hawksford cascode circuit? He wrote a neat article where he shows 20 dB improvement in Vas distortion from a fairly simple mod. I saw a very similar improvement in simulation. It's an interesting article to read, even if you don't use the circuit. I'd be glad to email it to you if you send me an email (since the forum email doesn't seem to work with attachments). |
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| PanzerLord |
| quote: | | Shouldn't R2 be in the source of Q1 instead of the gate? |
YES, of course, I did that in my 50W amp schematic (http://www.diyaudio.com/forums/show...&threadid=23673), don`t know why I put the resistor there???
(Sorry abot that John Curl!!!!!!!)
The reason there is 5 mA, I because I pasted the wilson from the amp schematic.....
I don`t think you just can use at the datasheet when determing Iref, I`ts better to replace R2 with a potmeter and measure the voltage over R3 or just put in some values the way I did..
And yes, I`m very interested in that schematic!!!!!:cannotbe:
my e-mail is:
frodeko@tiscali.no
THANX!!!!:) |
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| nowater |
| quote: | Originally posted by PMA
Correct. The same problem is with CD players. D/A residuals must be supressed. Preamp is to be designed the way it is not affected by RF and D/A residuals.
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What are the basic methods for supressing D/A residuals?
Grant |
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| Steven |
PanzerLord,
I think your current source is not as rock solid as you think. In your simulation with ideal battery power supplies the output current will be stable. In the real world any power supply ripple will modulate the current ouput of the JFET, since Vds will be modulated. The (almost) ideal Wilson current mirror will just copy the input modulated current into an output modulated current.
I also wonder what the purpose is of using a negative current source (i.e. with reference to the negative supply voltage) and then mirror it to get a positive current source. In this way you will have trouble to get rid of supply ripple. Why not just start with a positive current source? That could even be the same JFET. The JFET doesn't mind about polarity (being a floating current source) and will also act as a current source delivering current from its source.
Furthermore C1 in your diagram (in parallel to R3) makes no sense. It will only destroy the JFET during charging, since the JFET will get the full supply (minus 2Vbe from Q4/5).
Steven |
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| Christer |
Panzerlord,
unless you have already done it, I think it very wise to always
make additional simulations where you put signal sources
in series with the rails voltage sources and do an AC sweep
with these, both one at a time and both simulataneously. It
probably won't tell you the whole truth about sensitivity to
rail noise and variations, but I have found such simulations
very interesting and revealing in some cases. It is probably
a good idea to also try pulse sources and do transient analysis. |
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| Lelak53 |
This is my first contribution, hope you enjoy it.
Well, it's been said much on transistor sound, tubes, odd and even harmonics etc.
Personally, I not only belive in, but also can hear the diference between solid state and tube amplifiers.
Why? Although electronics design rules applied to audio amplifier design seem to lack
any revolutionary concepts since late 50-s and later "transistorized" tube designs
undergo many "improvements", there are still significant differences in designs around tubes
compared to solid state solutions. Let us disentangle some mysteries:
1. The emphesized "low THD" is NOT the exclusive attribute of transistor amplifier.
2. We have bipolar and (MOS)FET transistors and triode/penthode types of tubes. There
are some similarities between both worlds, but this worlds lay far apart of each other.
3. I could imagine to build a tube amplifier simulating a transistor amplifier.
4. If I had to build a transistor amplifier simulating a tube amplifier, I have a big trouble.
5. I belive what a musician says, when he says "this amplifier is not for me". In most cases
it is a transistor amplifier.
6. (MOS)FET is the sole generic transistor corresponding to a penthode-tube; I never heard of solid
state device comparable to a triode.
7. U/I characteristics are by far different, when comparing transistors and tubes (excluding
RF power tubes, as used in radio or TV transmitters).
This points (especially pt.6) are the main reason of differing sounds of the "two different worlds". |
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| millwood |
| quote: | Originally posted by Christer
Panzerlord,
unless you have already done it, I think it very wise to always
make additional simulations where you put signal sources
in series with the rails voltage sources and do an AC sweep
with these, |
a good ideal. I always do that to see how much "ripple" I get on the output from rails. |
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| PanzerLord |
| Yes, that`s a good point, I`ve done simulations with AC source..the results where very good, I`m not home right now, but I`ll post the results later. Thanks for more tips Christer... |
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| PanzerLord |
Well, I`m through testing (at least for the moment), and the results where somwhere close to what I ecxpected.
But I was wrong about the JFET though, so I have to give Steven credit for that one!!;) .
I also have second thoughs about the wilson current mirror as a current source for my amp after this....
Here what I`ve tested:
1.Wilson current mirror, with JFET current source (my "design")
2.Wilson current mirror as a current source
3.Vbe current source
4.Current source with transistor and two diodes Iref=0,7/R
dI=current variation through R3!
Numbers 1-3 where close, actally nr 1 came 3rd with dI=1.uA, nr. 2 had dI=0.67uA and nr. 1 dI=0.3uA.
Number 4 was so large I didnt bother to read the values, but I think the variations where around 30uA or something... |
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| millwood |
| quote: | Originally posted by PanzerLord
Numbers 1-3 where close, actally nr 1 came 3rd with dI=1.uA, nr. 2 had dI=0.67uA and nr. 1 dI=0.3uA.
Number 4 was so large I didnt bother to read the values, but I think the variations where around 30uA or something... |
but does it really matter? if the "norm" is 1ma, you are talking about very very small variation here. |
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| john curl |
| I'm glad that you found your typo. |
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| johnferrier |
| quote: | Originally posted by PanzerLord
Numbers 1-3 where close, actally nr 1 came 3rd with dI=1.uA, nr. 2 had dI=0.67uA and nr. 1 dI=0.3uA. |
Something seems wrong here.
nr 1 (came in 3rd): dI = 1 uA
nr 2: dI = 0.67 uA
nr 1: dI = 0.3 uA
The last one should be nr 3: dI = 0.3 uA, right? (I realize it is difficult to get every keystroke right.)
(nr 4: dI = 30 uA)
JF |
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| sss |
hey guys
what do u think of using op amp based currrent source in the lpt instead of a single transistors -diodes ? |
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| millwood |
| quote: | Originally posted by Lelak53
1. The emphesized "low THD" is NOT the exclusive attribute of transistor amplifier. |
may be there is a difference between performance under "repeatitive" sine waves, vs. real world music. transient reponses, for example, isn't as important with sine waves but is with music.
| quote: | Originally posted by Lelak53
4. If I had to build a transistor amplifier simulating a tube amplifier, I have a big trouble. |
I am not sure about this. There are empirical tests where people cannot tell the two amps apart. and I haven't seen the other way around.
| quote: | Originally posted by Lelak53
6. (MOS)FET is the sole generic transistor corresponding to a penthode-tube; I never heard of solid
state device comparable to a triode. |
that would be meaningful if the "configuration" of a tube contributes differences in sound.
| quote: | Originally posted by Lelak53
This points (especially pt.6) are the main reason of differing sounds of the "two different worlds". |
it may be too early to conclude that there is a "tube" sound (vs. ss amps of similar performance). tube amps tend not to performance well in higher frequencies so that may contribute to their "perceived" sound characteristics. Plus they do performn differently in clipping but that can be dealt with in a SS amp as well. |
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| AKSA |
Aside from clip performance, another major difference with a tube amp is damping factor, which contributes to the soft bass and long decay of tube amps.
If you take global feedback from the drivers (or the voltage amplifier) of a SS amplifier, you obviously increase the output impedance. You also improve its tolerance to reactive loads enormously. What is not realized is that the sonics then become very like a tube amp, with marvellous imaging, long decay and soggy bass. Some people love this sound of course; others don't. But it can actually be configured as fully adjustable; now that's an interesting concept!
Cheers,
Hugh |
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| fscarpa58 |
I agree Hugh
moreover, a high output impedance (low damping factor)
makes the freq. response of the amplifier very sensitive to variation in the impedance modulus vs. freq. curve of the speaker system.
once I had a Carver unit with a very low damping factor (8)
to emulate tube amp. sound. The result, was a lucid brilliant
sound in the range 2k-3k Hz where my speakers have a impedance peak, and a soft bass. However, it did not succed
to emulate well a tube amp. In any case, I think it is possible.
Federico |
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| jcarr |
Dear Hugh:
Some time in the 1980s, Luxman released a kit power amp called (I think) the A901. It was designed so that, at the touch of a front-panel switch, the user could choose between global feedback from the output devices, or a smaller feedback loop from the driver stage. You could also select between stereo and BTL mono, full Class A and rich Class AB.
From memory, the topology was input N-channel LTP with current-mirror summing, into a single PNP folded-cascode with an active load on the negative side, and then a Darlington PP output stage.
Fun toy to play with if you can find one.
best, jonathan carr |
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