PART FOUR:
There are still quite a few things that have influenced the development of this project, both the commercial JLTi and these two DIY versions – primarily the Tube version.
Some may ask, what is the differences between the JLTi and the DIY Tubed version?
For a start, the Tube Buffer in the JLTi is much more enhanced, the so-called SLCF enhancement. For a discussion of the SLCF and other good things, may I again refer you to my on-line essay:
http://members.ozemail.com.au/~joeras/tubes_&__the_gainclones.htm
Also this enhanced Tube Buffer needs higher voltages to work comfortably. Thus it is plus and minus 55V. It is also regulated, by using a version of the SuperReg, developed by the Vacuum State Electronics team headed by Allen Wright.
If you wish to regulate your Tube, then by all means go ahead. I have stuck to simplicity and if you want to go further, you have my blessing.
What follows may be theory and attempting to gaze into the dark. Nevertheless I hope it is of interest.
Subject: Lynn Olson’s “The First Watt”
For a couple of years the thoughts and writings of Lynn Olson has intrigued me, especially as they agree with much of my own. In March and April of 2000 he wrote two articles in the Glass Audio magazine. If you can acquire them, please do read them. I have a PDF file containing both of them, but for Copyright reasons I don’t feel right posting them on one of my web sites (I am the Webmaster for http://www.vacuumstate.com & http://members.ozemail.com.au/~joeras). Being 3.5MB in size would make for costly traffic costs. But if you have the opportunity to read these articles, don’t miss out.
Lynn Olson has a web site:
http://www.aloha-audio.com
But I digress. From his site I have borrowed this clip showing a distortion measurement of his Amity amplifier:
Caption: Amity PP Tube Amp. This is a 1Khz sine wave, 1.6W into 8 Ohm load.
The vertical scale is 10dB/division and lateral 1KHz/division. From this we can see that the 2nd harmonic is-70dB (0.03%) and the 3rd –65dB (0.05%). This is quite respectable, but what is noteworthy is the absence of higher-order distortion. There is just a hint of 5th harmonic at –82dB (0.008%). (The rest is either the noise floor or the limitation of measurement). This is commendably achieved without feedback. Compare this to more modern Push-Pull Ultra-Linear Tube amps (look at his web site as he provides sample measurements) are much more elevated in higher order distortions.
What Olson proposes is that the FIRST WATT is the MOST IMPORTANT WATT.
It makes basic sense. After all this is the part of the amp we are listening to ALL of the time. Higher power levels are more transient and shorter in duration.
Olson applies this to Tube Amps, but what about Solid State or Hybrid Power Amps? They do behave differently but what they may have in common is that feedback tends to reduce overall THD, but at the expense of higher orders being emphasized? So, while it reduces lower order distortion it pushes higher orders up. Even order harmonic distortion is very benign to the ear; odd order is less irritable if 3rd order rather than 5th order etc. So high odd order distortion must be suppressed and feedback may actually emphasize it even if overall THD is reduced. Do you get the general idea?
There is another difference; at 1 Watt virtually all Tube amps are still in Class A, whereas Solid State (and this applies here) will likely be beyond its Class A range and switching into B. So we expect Solid-State to increase distortion as we go DOWN in power whereas Tube tends to reduce. Solid-State likely decreases in distortion as power goes up (until it approaches clipping) whereas Tubes increase. Tubes, especially pure Triodes, are preferable in this respect.
So at 1 Watt crossover distortion will not be a factor in tubes, as per Lynn Olson’s premise, but with Solid-State Gainclone IC we would still hope for acceptable results at the same power. But a big BUT! What happens BELOW 1 or 2 Watt becomes critical with Solid-State. Distortion WILL increase; you can count on it. As we approach the point at which Class AB switching occurs (crossover) the large amplitude will not suppress these distortions (so they may not show up as well at 1 or 2 Watt and even less at 8 Watt etc). Will very low power levels see an increase in high order distortions?
This is what we will investigate here.
------------------------------------------------------------------------------------
How does our project fare with these factors in mind?
We start with 1 Watt:
Caption: This 1W into 8 Ohm load.
Distortion is primarily EVEN order, the only odd order showing up is the 3rd, and this is about 80dB down or 0.01% out of the total THD (Total Harmonic Distortion) of 0.114%.
Caption: This 2W into 8 Ohm load.
Much the same. Distortion is again primarily EVEN order; the 3rd is barely seen. Almost no difference except the note noise floor has been slightly suppressed as would be expected.
It is apparent that at these power levels, the First and Second Watt, our amp is very well behaved. There is a notable absence of ODD higher order distortion.
Before going on, I decided also to do a IMD (Inter-Modulation Distortion) test at 1W using 1KHz and 2KHz combined test signal:
Caption: This 1W approx into 8 Ohm load. IMD = 0.046%.
Again this looks excellent, no high real order irregularities.
BUT
So far so good. But what happens when we REDUCE power. This is a Class AB amplifier and so is prone to crossover type distortions. We need to examine THD at very low power levels.
Caption: This 125mW into 8 Ohm load.
This level means still Class AB (thus switching). As expected the noise is being suppressed less (this is a combination of the amp Signal To Noise Ratio and that of the test equipment) but around –90dB at this low level quite acceptable. No major increase in THD, indeed the slightly higher THD percentage is probably caused by the higher S/N. This is even better than I would have expected. Some pushing up of odd orders was anticipated and it hasn’t really happened.
Let us go much lower still:
Caption: This just 25mW into 8 Ohm load.
I also did 60mW and it was comparable to 125mW. But at 25mW it is most likely operating in Class A. Again S/N will be contributing to THD = 0.151%. An extremely small increase in 2nd and 3rd orders, and 4th is non-existent (or buried in the noise floor).
Caption: This only 10mW into 8 Ohm load.
Most definitely in Class A now. This seems confirmed by almost total lack of odd orders, but THD figure definitely influenced by S/N. But at this very low level indeed so no reason to complain about this result.
I am very happy with these results.
I did a series of these measurements as high as 47W and as low as 10mW and the consistency was remarkable. Here are the THD figures from all of them.
10mW - 0.177%
25mW - 0.151%
60mW - 0.139%
125mW - 0.125%
250mW - 0.120%
500mW - 0.113%
1W - 0.114%
2W - 0.111%
4W - 0.110%
8W - 0.109%
Distortion continues to drop gradually with increasing power, yet harmonic distortion pattern is always the same. The distortion harmonics ‘cascade’ like a waterfall, something that was recognized by insightful research decades ago (and subsequently forgotten) as sonically desirable.
Conclusion
Indeed, looking at all THD graphs (up to 32W) the results are consistent, 5th order or higher harmonics are superbly suppressed. In all cases the 3rd harmonic is lower than the 2nd (cascading) and the latter is repeatedly the dominant factor in the percentage of THD. This lack of odd order distortions is very welcome and the predominant EVEN order only tends to add very little ‘sweetener’ to the sound.
But what IF we go up in power level?
(Exceeding character limit)
Part Four continues....
There are still quite a few things that have influenced the development of this project, both the commercial JLTi and these two DIY versions – primarily the Tube version.
Some may ask, what is the differences between the JLTi and the DIY Tubed version?
For a start, the Tube Buffer in the JLTi is much more enhanced, the so-called SLCF enhancement. For a discussion of the SLCF and other good things, may I again refer you to my on-line essay:
http://members.ozemail.com.au/~joeras/tubes_&__the_gainclones.htm
Also this enhanced Tube Buffer needs higher voltages to work comfortably. Thus it is plus and minus 55V. It is also regulated, by using a version of the SuperReg, developed by the Vacuum State Electronics team headed by Allen Wright.
If you wish to regulate your Tube, then by all means go ahead. I have stuck to simplicity and if you want to go further, you have my blessing.
What follows may be theory and attempting to gaze into the dark. Nevertheless I hope it is of interest.
Subject: Lynn Olson’s “The First Watt”
For a couple of years the thoughts and writings of Lynn Olson has intrigued me, especially as they agree with much of my own. In March and April of 2000 he wrote two articles in the Glass Audio magazine. If you can acquire them, please do read them. I have a PDF file containing both of them, but for Copyright reasons I don’t feel right posting them on one of my web sites (I am the Webmaster for http://www.vacuumstate.com & http://members.ozemail.com.au/~joeras). Being 3.5MB in size would make for costly traffic costs. But if you have the opportunity to read these articles, don’t miss out.
Lynn Olson has a web site:
http://www.aloha-audio.com
But I digress. From his site I have borrowed this clip showing a distortion measurement of his Amity amplifier:
An externally hosted image should be here but it was not working when we last tested it.
Caption: Amity PP Tube Amp. This is a 1Khz sine wave, 1.6W into 8 Ohm load.
The vertical scale is 10dB/division and lateral 1KHz/division. From this we can see that the 2nd harmonic is-70dB (0.03%) and the 3rd –65dB (0.05%). This is quite respectable, but what is noteworthy is the absence of higher-order distortion. There is just a hint of 5th harmonic at –82dB (0.008%). (The rest is either the noise floor or the limitation of measurement). This is commendably achieved without feedback. Compare this to more modern Push-Pull Ultra-Linear Tube amps (look at his web site as he provides sample measurements) are much more elevated in higher order distortions.
What Olson proposes is that the FIRST WATT is the MOST IMPORTANT WATT.
It makes basic sense. After all this is the part of the amp we are listening to ALL of the time. Higher power levels are more transient and shorter in duration.
Olson applies this to Tube Amps, but what about Solid State or Hybrid Power Amps? They do behave differently but what they may have in common is that feedback tends to reduce overall THD, but at the expense of higher orders being emphasized? So, while it reduces lower order distortion it pushes higher orders up. Even order harmonic distortion is very benign to the ear; odd order is less irritable if 3rd order rather than 5th order etc. So high odd order distortion must be suppressed and feedback may actually emphasize it even if overall THD is reduced. Do you get the general idea?
There is another difference; at 1 Watt virtually all Tube amps are still in Class A, whereas Solid State (and this applies here) will likely be beyond its Class A range and switching into B. So we expect Solid-State to increase distortion as we go DOWN in power whereas Tube tends to reduce. Solid-State likely decreases in distortion as power goes up (until it approaches clipping) whereas Tubes increase. Tubes, especially pure Triodes, are preferable in this respect.
So at 1 Watt crossover distortion will not be a factor in tubes, as per Lynn Olson’s premise, but with Solid-State Gainclone IC we would still hope for acceptable results at the same power. But a big BUT! What happens BELOW 1 or 2 Watt becomes critical with Solid-State. Distortion WILL increase; you can count on it. As we approach the point at which Class AB switching occurs (crossover) the large amplitude will not suppress these distortions (so they may not show up as well at 1 or 2 Watt and even less at 8 Watt etc). Will very low power levels see an increase in high order distortions?
This is what we will investigate here.
------------------------------------------------------------------------------------
How does our project fare with these factors in mind?
We start with 1 Watt:
An externally hosted image should be here but it was not working when we last tested it.
Caption: This 1W into 8 Ohm load.
Distortion is primarily EVEN order, the only odd order showing up is the 3rd, and this is about 80dB down or 0.01% out of the total THD (Total Harmonic Distortion) of 0.114%.
An externally hosted image should be here but it was not working when we last tested it.
Caption: This 2W into 8 Ohm load.
Much the same. Distortion is again primarily EVEN order; the 3rd is barely seen. Almost no difference except the note noise floor has been slightly suppressed as would be expected.
It is apparent that at these power levels, the First and Second Watt, our amp is very well behaved. There is a notable absence of ODD higher order distortion.
Before going on, I decided also to do a IMD (Inter-Modulation Distortion) test at 1W using 1KHz and 2KHz combined test signal:
An externally hosted image should be here but it was not working when we last tested it.
Caption: This 1W approx into 8 Ohm load. IMD = 0.046%.
Again this looks excellent, no high real order irregularities.
BUT
So far so good. But what happens when we REDUCE power. This is a Class AB amplifier and so is prone to crossover type distortions. We need to examine THD at very low power levels.
An externally hosted image should be here but it was not working when we last tested it.
Caption: This 125mW into 8 Ohm load.
This level means still Class AB (thus switching). As expected the noise is being suppressed less (this is a combination of the amp Signal To Noise Ratio and that of the test equipment) but around –90dB at this low level quite acceptable. No major increase in THD, indeed the slightly higher THD percentage is probably caused by the higher S/N. This is even better than I would have expected. Some pushing up of odd orders was anticipated and it hasn’t really happened.
Let us go much lower still:
An externally hosted image should be here but it was not working when we last tested it.
Caption: This just 25mW into 8 Ohm load.
I also did 60mW and it was comparable to 125mW. But at 25mW it is most likely operating in Class A. Again S/N will be contributing to THD = 0.151%. An extremely small increase in 2nd and 3rd orders, and 4th is non-existent (or buried in the noise floor).
An externally hosted image should be here but it was not working when we last tested it.
Caption: This only 10mW into 8 Ohm load.
Most definitely in Class A now. This seems confirmed by almost total lack of odd orders, but THD figure definitely influenced by S/N. But at this very low level indeed so no reason to complain about this result.
I am very happy with these results.
I did a series of these measurements as high as 47W and as low as 10mW and the consistency was remarkable. Here are the THD figures from all of them.
10mW - 0.177%
25mW - 0.151%
60mW - 0.139%
125mW - 0.125%
250mW - 0.120%
500mW - 0.113%
1W - 0.114%
2W - 0.111%
4W - 0.110%
8W - 0.109%
Distortion continues to drop gradually with increasing power, yet harmonic distortion pattern is always the same. The distortion harmonics ‘cascade’ like a waterfall, something that was recognized by insightful research decades ago (and subsequently forgotten) as sonically desirable.
Conclusion
Indeed, looking at all THD graphs (up to 32W) the results are consistent, 5th order or higher harmonics are superbly suppressed. In all cases the 3rd harmonic is lower than the 2nd (cascading) and the latter is repeatedly the dominant factor in the percentage of THD. This lack of odd order distortions is very welcome and the predominant EVEN order only tends to add very little ‘sweetener’ to the sound.
But what IF we go up in power level?
(Exceeding character limit)
Part Four continues....
Part Four continues....
Max Power Test:
What if we push it to the limit, like more than 40 Watt?
Caption: 47W & THD = 1.324%
WHOA!What has happened here? Looks kinda ugly but actually not all bad news. The scope shot next explains all:
Caption: 19.5V RMS into 8 Ohm = 47W.
Notice that the scope shows that the amp is NOT clipping? So what is happening to the top and bottom of the waveform? It is actually 100 Hertz ripple intruding (double the Mains frequency) when the power supply is required to deliver peak current. You can see this modulating the 1KHz waveform and if you look carefully the lines are lateral and low frequency in content. Because we are using smaller than usual 1000uF reservoir caps, these caps are depleting, creating the above effect. But music signals are NOT continuous like our test signal. So we would expect that short music peaks might well be left unaffected. So the amp is easily capable of 35 Watt RMS (continuous) and short-term music peaks of 50 Watt.
The use of such small reservoir caps may seem controversial, yet using higher values may well be lowering the time constant (slower) caused by the combined AC source impedance of the power transformer and rectifier bridge. The problem is that this is a complex dynamic inter-face as it is governed by both the charging cycles and interfered by the DC current requirement of the amplifier itself. I would love to see someone model this mathematically, could make for some interesting reading.
This is not exactly new thinking. I recall some fifteen years ago that Martin Colloms (of HFN & RR) writing on this very subject and he demonstrated to himself, as I recall it, how he could make sonic changes by varying the wire gauge between the Bridge and Reservoir caps. As far as using small caps in our Gainclones, I do know this, it has a great agility in the mid-bass that makes it as good as anything when playing acoustic or even electric bass, and other instruments that require good sense of pitch, pace and tonality.
Final
So here are by reason some good pointers to the more than acceptable sound quality of these little wonders. I have said to myself many times over that they don’t deserve to sound as good as they DO. After all, this is a feedback amp, indeed an Op-amp device where Feedback is THE controlling element as to gain. It is also Push-Pull (derision from certain quarters), Class AB (more derision) and not much of it is Class A (probably about 0.03W) as the idle current is only slightly more than 30mA. So while it breaks the mold in many ways there are also some good indicators. The use of Current Sources (six) and Class A in all stages up to the Quasi Output Stage (NOT complimentary). The Constant Current Class A Driver (to the Quasi out) used internally must be very good in absorbing crossover artifacts as they look so well suppressed, no real increase with descending power, in 3rd order but also 2nd order which continues to dominate. At all levels it is the 2nd and 4th combined even orders that define the measurements. Excellent!
But measurements are not everything, it is the SOUND that is the final arbiter! That is why the commercial equivalent is called JLTi. So all I can say is “Just Listen To It.”
So there you are.
THE END.
PS: All four parts of this project that has been posted here will SOON be condensed into a Web Site. Not sure what name to give it, but maybe “The DIY Tube Gainclone”. OR: “Tubes and The Gainclones”. Suggestions welcome.
The address and space has already been secured, it will be http://members.ozemail.com.au/~lisaras . Come and see us soon.
Max Power Test:
What if we push it to the limit, like more than 40 Watt?
An externally hosted image should be here but it was not working when we last tested it.
Caption: 47W & THD = 1.324%
WHOA!What has happened here? Looks kinda ugly but actually not all bad news. The scope shot next explains all:
An externally hosted image should be here but it was not working when we last tested it.
Caption: 19.5V RMS into 8 Ohm = 47W.
Notice that the scope shows that the amp is NOT clipping? So what is happening to the top and bottom of the waveform? It is actually 100 Hertz ripple intruding (double the Mains frequency) when the power supply is required to deliver peak current. You can see this modulating the 1KHz waveform and if you look carefully the lines are lateral and low frequency in content. Because we are using smaller than usual 1000uF reservoir caps, these caps are depleting, creating the above effect. But music signals are NOT continuous like our test signal. So we would expect that short music peaks might well be left unaffected. So the amp is easily capable of 35 Watt RMS (continuous) and short-term music peaks of 50 Watt.
The use of such small reservoir caps may seem controversial, yet using higher values may well be lowering the time constant (slower) caused by the combined AC source impedance of the power transformer and rectifier bridge. The problem is that this is a complex dynamic inter-face as it is governed by both the charging cycles and interfered by the DC current requirement of the amplifier itself. I would love to see someone model this mathematically, could make for some interesting reading.
This is not exactly new thinking. I recall some fifteen years ago that Martin Colloms (of HFN & RR) writing on this very subject and he demonstrated to himself, as I recall it, how he could make sonic changes by varying the wire gauge between the Bridge and Reservoir caps. As far as using small caps in our Gainclones, I do know this, it has a great agility in the mid-bass that makes it as good as anything when playing acoustic or even electric bass, and other instruments that require good sense of pitch, pace and tonality.
Final
So here are by reason some good pointers to the more than acceptable sound quality of these little wonders. I have said to myself many times over that they don’t deserve to sound as good as they DO. After all, this is a feedback amp, indeed an Op-amp device where Feedback is THE controlling element as to gain. It is also Push-Pull (derision from certain quarters), Class AB (more derision) and not much of it is Class A (probably about 0.03W) as the idle current is only slightly more than 30mA. So while it breaks the mold in many ways there are also some good indicators. The use of Current Sources (six) and Class A in all stages up to the Quasi Output Stage (NOT complimentary). The Constant Current Class A Driver (to the Quasi out) used internally must be very good in absorbing crossover artifacts as they look so well suppressed, no real increase with descending power, in 3rd order but also 2nd order which continues to dominate. At all levels it is the 2nd and 4th combined even orders that define the measurements. Excellent!
But measurements are not everything, it is the SOUND that is the final arbiter! That is why the commercial equivalent is called JLTi. So all I can say is “Just Listen To It.”
So there you are.
THE END.
PS: All four parts of this project that has been posted here will SOON be condensed into a Web Site. Not sure what name to give it, but maybe “The DIY Tube Gainclone”. OR: “Tubes and The Gainclones”. Suggestions welcome.
The address and space has already been secured, it will be http://members.ozemail.com.au/~lisaras . Come and see us soon.
Joe,
It would have been interesting to do these measurements on a "normal" non-tubed gainclone and compare them side by side with your tubed version. That should be worthwhile to prove your points.Otherwise a set of good measurements is of course a good sign but it doesn't prove any of your theories regarding upgrading the simple gainclone.
It would have been interesting to do these measurements on a "normal" non-tubed gainclone and compare them side by side with your tubed version. That should be worthwhile to prove your points.Otherwise a set of good measurements is of course a good sign but it doesn't prove any of your theories regarding upgrading the simple gainclone.
protos said:
Thank you for your interest.
Frankly I don't think the measurements would be all that different. But to set the record straight, I did build two IGCs based on Thorsten's circuit (I had a childhood friend called Torsten) and did do some, but not as exhaustive tests.
I wasn't actually trying to prove that the tubed version would measure different OR better (in the sense that some might find adding EVEN order distortion an improvement, which I don't). Instead I was concentrating on why these ICs sound as good as they do, tubed or sans tube.
I am not saying I was totally successful, indeed I did say I was gazing into the dark.
I believe that the Tube version sounds better because of the overall implementation, not just THD measurements.
Joe
From your observations it seems that the gainclone would work better from a normal pre-amp as this would in fact buffer the input and provide a low Z source.How would the input cap to ground be then implemented ? I am currently using a Pass Balanced Line Stage with an output 10 k pot and feeding a balanced signal to the gainclone which to my ears is much much better than the single ended signal I have tried either with a passive pre or with the Pass BLS.
My first thought upon looking at this version was to substitute the cathode follower from a tubed active crossover, and make a compact, all-in-one, crossover/amp containing both lowpass and highpass amps in a single box. Unfortunately, I don't know if a 6dj8 or 6N1p could "drive" the network with 35 - 55V on the plate.
...and the PSU might start getting messy...
...and the grounding...
...and the PSU might start getting messy...
...and the grounding...
protos said:
Not necessarily work better but you've got the general idea. Indeed I would consider it an option to do my NON-tubed version but using the exact component values of the TUBED version, particularly 4K7, 18K and 1n3. Where the pot is you must fit something like 47K to ground. The downside is more ideological, namely that the buffer should be nice and close... but hey, we live in the real world.
Contstant Low Z (or at least 'constan't as in not changing like a pot) should be the first aim, IMHO.
Is this 10K right on the output and thus defining Output Z?
The Gainclones done so far have all been single-ended, so no way to drive them from a balanced source. Can a gainclone be made that can? Sure, but that is a totally new project - although the topology is well known and has both up and downsides.
Is this the Pass Line Stage you are using:
http://www.passdiy.com/pdf/balzenpre.pdf
... with the optional 5K pot dual pot per channel (but actually using more common 10K)?
Joe
Home on the range... where the....
"The Tube Gainclone for DIY Buffs" now has its own permanent home.
The address is:
members.ozemail.com.au/~lisaras
(Don't forget to Bookmark it
)
Joe Rasmussen
"The Tube Gainclone for DIY Buffs" now has its own permanent home.
The address is:
members.ozemail.com.au/~lisaras
(Don't forget to Bookmark it
)Joe Rasmussen
Joe, may I add my thanks for your work on the hybrid chip amp design which I will be attempting.
I have always favoured placing the PSU section of an amp into a separate case but it does add significantly to the cost, almost disproportionately so in the case of the low-cost chip amp designs.
Once you add an AC supply for the tube section, things get even more costly with the extra connectors etc so can I ask you if, in your experience, the separation of the PSU and the amplifier circuits into different cases does make a big difference?
I have always favoured placing the PSU section of an amp into a separate case but it does add significantly to the cost, almost disproportionately so in the case of the low-cost chip amp designs.
Once you add an AC supply for the tube section, things get even more costly with the extra connectors etc so can I ask you if, in your experience, the separation of the PSU and the amplifier circuits into different cases does make a big difference?
Well, while we're on the subject of topology, let me ask the same question about my plan.
Mine will have 4 xformers, all EI, 1 for each 3875, 1 for the tube B+/B-, 1 for the filament. I am planning to make my own case, tube & heatsinks on the outside, everything else inside. I was not planning to segregate/shield the xformers.
Will this layout run into problems? Should I build my case with internal dividers to provide shielding? If yes, which section should be shielded from the others: PS, tube, or chip?
Mine will have 4 xformers, all EI, 1 for each 3875, 1 for the tube B+/B-, 1 for the filament. I am planning to make my own case, tube & heatsinks on the outside, everything else inside. I was not planning to segregate/shield the xformers.
Will this layout run into problems? Should I build my case with internal dividers to provide shielding? If yes, which section should be shielded from the others: PS, tube, or chip?
I've decided that it's going to have to be in the kinda distant future. My idea being to use the cathode follower of a tubed x-over as the buffer, and having an all-in-one monoblock(xover, and two amps driving a yet to be designed speaker). Look forward to hearing your results. Have you already built a "standard" gainclone?
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