| Hello all, hows about helping a newbie - Click HERE for Original Thread |
| justblair |
Hi all.
I have a set of Mission 753 (non-freedoms) and currently use a Musical Fidelity E100 amplifier with them. I like the sound, especially after doing the ever so simple tweeter mod on them, but the gainclone interests me. I just like to get my hands dirty. Some questions.
The setup I envisage (ultimately) will be 4 monoblocks driving the missions, each bi-amped. I'm thinking probably that I will go down the SMPS route, rather than building my own supply. (Decible Dungeon has been a fantastic resource so far) I may wish to go further in the futiure and bypass the speakes passive filters. But one thing at a time.
Now I am more or less ready to get going. I need some advice on the smps arrangement.
Decible Dungeon suggests using skynet 8080's, and I can get hold of them at reasonable prices. I was considering using 4. Either to produce +/-24v. or to produce 2x+/-12v. Im thinking also about using a linear regulator for each amp
As the missions are rated at 6ohm I'm fairly sure that the LM3886 chip is the one for me. The LM3875 seems from what read to prefer 8ohm.
Questions...
1. Am I right in saying that the LM3886 really needs at least 20v? If so I am looking at using the skynets at 24v.
2. Will the 24v arrangement supply enough VA for running 4 amps?
3. Is using linear regulators after the skynets just getting silly?
4. Other advice?
I know that someone will advise that I should be starting simple and working up to this, but as power supplies are the expensive bit, I'd rather start off high quality here than buy up (reasonably expensive torroids and diodes) only to scrap them. I will do my experimentation at the cheaper stuff on the amps.
Long first post I know, but advice would be good. |
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| Nuuk |
LM3875 (yes) with +/-24 volts from four Skynet 8080 modules. That will run your Mission 735s fine.
No linear regs.
Try that, then if you want a spearate PSU for each channel, add another four Skynet 8080s. ;)
(I took pity on you with a name like that! :D ) |
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| AndrewT |
| quote: | Originally posted by justblair
I may wish to go further in the future and bypass the speakers' passive filters. But one thing at a time.
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Hi,
go read the last 24hrs posts in DCX2496 thread.http://www.diyaudio.com/forums/show...&threadid=15943
You may decide that passive bi-amping is as far as one may want to go.
I tried DCX active route and reverted back to passive, but I was not nearly as thorough as Pqr in post1054, 1056, 1057. |
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| justblair |
@NUUK Thanks for the advice, I was doubting the need for regs, due to the voltage drop more than anything. As for the LM3875, I had discounted that due to its reqirement for 8ohms.
Do I take it that 2ohms difference wont effect them badly in your opinion?
Does an inverting design make more sense in my case?
And thanks for the pity
:xeye: :)
@Andrew... Thanks for the heads up... I have not got far into my research regarding active crossovers, I will think very carefuly now before attempting such a thing!
Open to any other advice... Particularly a few opinions on the chip choice. |
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| Nuuk |
Yes, the LM3875 will be fine with 6 ohms - as I recall the 753 is not a difficult load.
I have a pair of IPL A2 kit speakers. They use pretty much the same drivers as the Mission 752 and I drove them from LM3875 amps with no problem.
As regards this active crossover business, I have said this a few times now but we know how easy it is for posts to get 'buried' on such a popular forum so I will say it again.
Going active is not just a matter of removing the passive crossovers and using active ones in their place. The removal of the passive crossovers can, and does change the speaker alignment. With a sealed box speaker, this usally isn't a problem but with a ported design, it can mean that you need to change the volume of the speaker cabinets, usually making them larger.
As an example, my A2 speakers with passive xovers had a cabinet volume of 27 litres. After moving to active xovers, I found the best size (by trial and error) was around 33 litres. Oh, and the port tuning needs altering too!
I can honestly say that I achieved very good reslts with my active A2s using nothing more than the simple discrete crossover that is described here
(you could try opamps instead) Of course, I may just have been lucky but for a two-way speaker, it is worth a go for what is involved!
End of sermon! :D |
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| justblair |
@NUUK thanks again, especially for such promptness in your reply. Funny enough I have DD open in another window ATM and was just reading on your experiances tuning the enclosures.
I dont see me going active in a hurry (if at all), I like when I start a project to know where it is going and plan for where it might lead. Once I have bored myself playing with the amp, I may try the active route... Following in your footsteps though I can see a preamp with a buffer being the next logical step.
I dont want to try and reinvent the wheel right away. I am in the early learning centre of the diy electronics high street right now. I recently taught myself the basics on PCB manufacture (photo resist) and this is an opportunity to use and refine my newly aquired skills.
DD by the way is a fantastic resource, you should be proud. My decision to take up this project was hugely influenced by your site. Your writing style and the structure of the site really makes a project like this seem both attainable and desirable. Hope I dont sound too sooky, but I like to give credit where its due!
Blair |
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| Nuuk |
Thanks Blair, there are quite a few hours in the old Dungeon so I am very pleased when I hear that it has been of help and inspiration to others.
I think getting started is the hardest part of this hobby, and I intentionally wrote DD to help people over the first hurdle! ;)
And you are doing the right thing in concentrating on one part of your system at a time. :) |
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| justblair |
Ok...
I have a few more questions. Here is my shopping list so far...
4 x Skynet 8080 (on route to me right now)
4 x Lm3075 (on route to me now)
8 x 1000uf Nichicon fine gold caps (in my grubby paws)
4 x Maxim ds1802 Digital volume controls (samples requested)
4 x QT110 touch sensors
My plan is to run the signal (Pc source) through the Maxim volume controls, to a buffer and then to the 4 lm3875 circuits probably IGC configeration.
The DS1802 I was planning to use in the circuit described by Pedja Rogic
DS1082 circuit
I was thinking along the lines of having two of these running, one per opamp (ie per channel) daisychaining them to get unversal control. In the future this would also give me the option of using remote control
Next off I will use the simple discrete buffer described at Decibel dungeon
Simple buffer here
Then into the IGC circuit at the same site.
Power comes from the SKynets, set up to run 24v, The buffers regulated down to +/-15v.
I will regulate the 5v supply from the Skynets down to +/-2.5v for running the DS1802 chips and the QT110's
Questions.
1. Are there any advantages in running 4 op amp stages ie. one per power amp?
2. What is the imput impedence of the discrete buffer?
3. Am I going to run out of power from the Skynets?
4. Can you see any other nasties ahead for me? |
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| justblair |
Up and running now with 4 SMPS and two IGC amps, having so much fun on this thanks for the help so far.
I thought I would share my early experiances on using SMPS. I had the option to try out differnet combinations of the Skynet 8080. I used of course Decibel Dungeons instructions to wire up.
One unmodded SMPS feeding two amps - Not brilliant at all, although initial impressions were that the amps were bright and engaging, clipping came very quickly. Later experiments showed also that detail was missing throughout the frequency range.
Two unmodded SMPS feeding two amps - Better. The brightness was still there, and clipping was less evident. However the detai was poor in the bass range. NUUK described this as flabby and I tended to agree, My flatmate however pointed out that the bass sounded compressed. As soon as he said it, it struck me that he was right.
Two modded SMPS in series feeding two amps - Things got a whole lot better in the Bass range having +/- 6amps available. Though the bass was flabby still, the compression had reduced dramatically. The sound was still very bright though smooth and I thought it was engaging and very musical, especially with Jazz and female vocals. That was untill I tried 24v from 4 SMPS.
This is where my experiance differs from NUUK. The 24v option was dramtically better on my setup. The controll over the bass was suddenly happening, But not just that, the top end improved as well. Although previously I thought that the 12v sound had been detailed it now seemed unsubtle. What I had mistaken for smoothness before was obviously a blurred sound. NUUK mentioned on his site that he would be pushed to choose between 12v and 24v, In my setup the choice is far clearer. Regardless of the type of music being played the 24v setup is several times better. The 12v is upfront and in your face, switch to 24v the soundstage goes back the way, deep behind the speakers. The imaging is so much better as well.
I have also tried a zobel network with 10r and .1uf cap. I am not sure if I am supposed to hear a difference. I think I do, but I have listened now to so much I think that I might be imagining it.
Plan is next to introduce a buffer to the mix to see if it improves things further. Its hard to imagine it will, but the parts are all sitting here in plastic baggies so might as well give it a go.
Thanks again all!
Blair |
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| AndrewT |
Hi,
the Zobel should not be heard.
It should help stop oscillation.
If oscillation did occur you might hear the remanants down in the audio band.
It sounds like the chipamps are sensitive to PSU and particularly low supply voltage (=lots of clipping on transients) and lack of current. Are you allowed to add smoothing capacitance between the reg and chipamp?
My camp and the other disagree on how much capacitance is needed to support good bass.
Have you tried them on an unregulated supply yet? |
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| justblair |
I haven't tried them on an unregulated supply as yet. probably wont have that opportunity for a while. When I put together my parts list I wanted to build as good an amp for the money as I could.
NUUK's site convinced me that the SMPS route was the easiest way to get high quality sound. I got the four SMPS for such a good price, it was as cheap as going for a simple unregulated supply.
Cap wise I have gone for the classic 1000uf power supply caps. They are bypassed by .1uf polyesters. Not a whole lot of power there, but the SMPS running on 24v dont seem to have any problems with transients. I may play a bit with some extra smoothing on the caps once I have the rest of the system working.
Been making a start on the case today. Got some white oak cut for the sides of the case, going to match that up with polished sheet alu for the top and bottom. This "base" will hold the SMPS. Then polished alu "project" boxes mounted on the top of that for each amp stage. The idea is to keep everything as seperated as possible whilst still having an integrated amp.
Its starting to look pretty damn good. I think it will look pretty exotic when I get it all built.
I will spend some more time tring out the zobel. Its probably just my imagination thats creating differences. |
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| alleycat |
| Hi justblair, I'm waiting for an SMPS to arrive in the mail and have been wondering about what to do about the bypass caps. I was thinking of replacing the 1000uF caps with 100uF bypassed with 0.1uF. I'm hardly an electronics expert but I've seen this setup used with other types of power supply (eg BrianGT's LM3886 kits) and thought it might be appropriate for the SMPS. I also read in some SMPS documentation that there should also be 100uF and 0.1uF on the output of the supply as well. |
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| davidlzimmer |
| quote: | | I think getting started is the hardest part of this hobby, and I intentionally wrote DD to help people over the first hurdle! |
Wrong! Over comming the addiction is the hardest part! :D
But, who's trying! :devilr: |
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| justblair |
| quote: | Originally posted by alleycat
Hi justblair, I'm waiting for an SMPS to arrive in the mail and have been wondering about what to do about the bypass caps. I was thinking of replacing the 1000uF caps with 100uF bypassed with 0.1uF. I'm hardly an electronics expert but I've seen this setup used with other types of power supply (eg BrianGT's LM3886 kits) and thought it might be appropriate for the SMPS. I also read in some SMPS documentation that there should also be 100uF and 0.1uF on the output of the supply as well. |
You are bit by chance the same alleycat that posts around SPCR?
For my caps I just followed the circuit on Decibel dungeon. I have not put any on the supply output.
I did think about using lower values on the voltage rails, I may give it a try |
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| alleycat |
| Yes, it's me, the creator of the "alleycat enclosure". Caught the audio bug after reading an off topic thread on SPCR a while ago. One thing led to another and I found this site! I seem to spend more time lurking around here these days. |
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| justblair |
LOL
I got the electronics bug in a similar fashion. Learned to make pcb's so that I could make a IC linked thermometer for another project.
Hope that you are as creative with the audio stuff as your enclosure required. I made one and as I am sure you know I cant sing its praises enough.
Blair |
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| alleycat |
| Thanks for your compliments. It's great to have a PC that's completely inaudible, something I've noticed most people around here aren't too familiar with. I'm sure their CD players make much more noise than my computer does! Having a silent PC has really opened my mind to the possibilities of computer hifi. The missing link seems to be a good, affordable USB DAC. |
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| alleycat |
Thanks for the link... although I'm getting right off topic.
I hope we'll hear more about justblair's SMPS experiments! |
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| Nuuk |
| quote: | | Thanks for your compliments. It's great to have a PC that's completely inaudible, something I've noticed most people around here aren't too familiar with. |
Is this something we can all do? Is it expensive? And can you point us to details of exactly what you have done to your PC? ;) |
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| justblair |
| quote: | Originally posted by Nuuk
Is this something we can all do? Is it expensive? And can you point us to details of exactly what you have done to your PC? ;) |
Anyone can silence a pc and it neednt be expensive. Though it can be as addictive as DIY audio, I have built two. One which is barely audible and a passive cooled one which is to all purposes silent.
SPCR Is a good website for starters, It is a very active and generally friendly place. The off topic section gets a bit heated though.
Here are my two silent pcs
My passive pc playstation hybrid
My stealthed near silent bedroom pc
And back on topic, I have the beginings of a case made for my newbie Decibel Dungeon designed amp
Back
Front 1
Front 2
Front 3
Still some work to be done |
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| Nordic |
Erm, try some chip buffers with good noise rejection like opa2227 (gains under 5) opa2228 (for more).
The noise rejection from my pc compared to other chips I used was remarkable. |
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| justblair |
| quote: | Originally posted by Nordic
Erm, try some chip buffers with good noise rejection like opa2227 (gains under 5) opa2228 (for more).
The noise rejection from my pc compared to other chips I used was remarkable. |
Thanks Nordic, though I think that some cross purposes are happening here.
The thread has gone a little off topic, Alleycat and I are not talking about signal noise from the PC but rather fan noise.
I am not too bothered about going OT. In fact the silent PC is an area I feel far more knowledgable in, happy to trade silent PC for DIY audio advice. I feel in debt to NUUK already, would welcome an opportunity to pay him back. |
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| alleycat |
Hi Nuuk, I've spent plenty of time looking around your site also, so I'd be glad to pass on what I know about quiet computers. The principles are pretty basic, and you just need to know about a few products that will help keep the noise down.
There are two main causes of noise in a PC, both of which are caused by moving parts: there are cooling fans, and there are disk drives. To minimize the effects of fans, we need to first minimize the heat output of the PC by selecting components which do not create much heat in the first place. Some processors dissipate less heat than others. The same can be said for graphics chips. When overall heat output is lower, less airflow is required to remove the heat, so slow fans can be used.
The use of efficient heatsinks on hot components allows us to make the most of the bare minimum of airflow. Also, there should be a clear airflow path through the computer case. Things like cutting out grilles and tidying cables can assist here. It is surprising how poorly designed many cases are in this regard. Air usually flows in at the bottom front of the case, and out the back near the top, moving past the main hot components on the way.
The hard disk is a major cause of noise due to the high speed motor it contains and the movement of the read-write heads. Due to all this movement, the drive also tends to vibrate, and this is transmitted to anything else it touches. Because the drive is usually screwed into a drive bay, the vibration is coupled to the entire PC case, which then resonates. Just by decoupling the drive from the case, a huge component of the PC's noise is removed. This can be achieved by suspending the drive inside the case using elastic or shock cord. Even with suspension, in a very quiet PC, the drive will still be somewhat audible (varying with make and model), so to completely dampen its noise, it needs to be placed in an enclosure. Even then, the enclosure will often need to be isolated from the case, so insidious are the drive's vibrations.
Once a PC has been built/modified for quietness, it should be tested to ensure that all temperatures remain within comfortable limits, even under heavy loads. |
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| alleycat |
A PC used mainly for audio doesn't need a lot of processing power. However, I would consider a Pentium 3 to be a practical minimum. There are plenty of old computers around which could be modified using the principles I mentioned above, YMMV. I can't really comment on every configuration that's out there, so I'll briefly describe building a budget system based on currently available parts. It's worth spending some time over at SilentPCReview to check out the latest info.
The PC will be based around a Sempron processor. The exact speed doesn't matter, I'd just get the cheapest or second cheapest model. The processor needs a matching motherboard. You can get some great combo deals from computer shops or on eBay. I recommend getting a "micro-ATX" motherboard, as they are smaller and usually have built-in graphics. Some will also have built-in SPDIF which could come in handy. The main thing is to make sure there are no fans on the motherboard, as they can be incredibly whiny. You should be able to tell by looking at a photo of the motherboard - there should be a finned heatsink in the middle.
The Sempron will come with a heatsink and fan. These can be discarded. In their place use a Scythe Ninja. The Ninja is supplied with a fan, which is not actually needed.
I always choose the cheapest micro-ATX case that I can stand the look of (so many cases are incredibly ugly!), and make any necessary modifications. Stamped metal grilles will usually need to be cut out and replaced with screw-on wire ones. There may be other restrictions to airflow that will need sorting out. The case will usually include a power supply unit. The PSU contains a fan, and this is what will pull air through the case. Depending on the design of the PSU, there should be a fan on the underside of the unit pulling air in, or one blowing out the back with an intake grille on the underside. Either way, we're aiming to make sure there is a bit of airflow through the Ninja's fins. If there are ventilation holes on the side of the PSU where the coloured cables come out, then these should be taped over. All the air will then be sucked in from the underside of the unit and exhausted out the back. The PSU's fan will also need to be replaced with a quieter one (:att'n: Danger: high voltages inside PSU. Warranty will be void). We'll do this after we're sure we've got the PC working.
Finally, the hard drive. I'm a big advocate of enclosures (note that I'm not talking about the external type for USB at this stage), and I've come up with my own design. There are a few commercially available units, such as the Scythe Quiet Drive. It's worth finding a good enclosure, as some don't work well and some cause the drive to overheat a bit. Also, it's not a bad idea to get a drive that's relatively quiet in the first place. I think the Samsung T series is the current favourite (320GB, enough for about 700 CDs stored with FLAC). For the ultimate in quiet, a laptop drive is the go. However they are expensive, slower and come in smaller capacities. It all depends on how much music you want to store. If you're serious about safeguarding your collection, get an external USB drive as well so that you can periodically make a back up.
To complete the PC we'll also need memory (at least 512MB), and an optical drive, which may as well be a DVD burner. Obviously we'll need a monitor, mouse and keyboard. Once assembled, the PC can be fired up so that we can get into the BIOS. If the PC doesn't start, it might need to sense a fan on the CPU fan header, so just plug a fan in there for the time being. Once we get into the BIOS, it should be possible to disable the fan sensing. The boot order also needs setting so that it will boot from the optical drive before the HDD.
Of course, we're not going anywhere without an operating system. I happen to have Windows XP and iTunes, which is probably not the ideal way to do things, as this costs money if you don't already own a copy. Xubuntu with appropriate ripping and playing software would be a good option, and details on how to run these are all over the net.
Once the operating system has been installed, we can perform the PSU mods. If the PSU fan is a 120mm type, then we can use the fan that came with the Ninja. It will need to be connected to 5V (there is a 5V rail inside the PSU), instead of the usual 12V. This will slow it down to the point of being inaudible. If the PSU contains an 80mm fan, it will need to be replaced with a Nexus. These 12V fans need a minimum of about 7V to run, so we can either opt for the full 12V which is still reasonably quiet, or go the extra mile and put a few diodes in series to lower the voltage a bit.
Now that we're happy with the noise levels, it's a good idea to stress-test the system. I use Prime95 and run it for 24hrs, keeping an eye on the temperatures every now and then, although the system will usually max out after about half an hour (my enclosure takes about 2hrs to reach maximum temperature however). If the hard drive stays below 40degC and the CPU stays below 60degC without any Prime95 errors, then the system can be considered stable.
Hook up a good quality USB DAC and you'll never need to touch a CD player again. |
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| BWRX |
I thought you were taliking about making a PC electrically silent, meaning it spits out less RF and other junk on the power line ;)
As far as acoustically silent, you've covered most of the bases. Fans are the big issue and hard drives are the next hurdle. Reducing fan speed is one way but also providing adequate clearance for the fan to operate (make the distance between the fan blades and the nearest object as large as possible) can reduce audible noise - especially at the fan's inlet. Less blades also lowers the frequency at which you hear it operating.
Another option is to get an apple laptop with optical audio output ;)
While a PC has lot to offer, a quality standalone CD player still has its advantages. |
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| Nuuk |
Thanks guys for all the tips on making a PC as quiet as possible.
The reason I asked is because recent reviews I have been doing of PC audio products have led me to believe the CDP has had its day!
I currently have my main computer and a PC music server running here but want to run everything from a single PC for what should be obvious reasons.
You only have to look around the hi-fi forums to see that there is a strong trend toward PC based audio, whether it is using a soundcard, USB DAC, or music streaming device such as the Squeezebox. So this sort of discussion is valid on a hi-fi forum, even if we have hi-jacked Blair's thread.
My main PC is currently sat on top of a twin-pedestal desk and despite some efforts to quieten it, it is noisy enough to drown out the noise of my music server, despite the latter being closer to my listening chair. What I intend to do is remove the draws from one of the pedestals and make a false front, at the same time removing the back panel. The PC would then go into this space with lots of that noise absorbing material.
I will also use some of the suggestions in alleycat's posts to reduce the noise of the PC further.
Anyway, I've got an appointment with the dentist so I'd better get going! ;) |
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| AndrewT |
Hi,
how do we make the PC output electrically quiet?
So that one can listen to the wanted signal. |
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| alleycat |
| I'd also like to know the answer to that question, and that is one reason why I am interested in a USB DAC (if that is in fact a solution). Right now I'm listening to Rachmaninov's Vespers through an M-Audio Revolution 5.1 soundcard inside my PC. If I turn the volume on the amp right up, I can just hear some interference from the PC's circuitry in the background. It seems to be related to what's happening on my screen. Not normally a problem, but it would be nice to get rid of it. |
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| AndrewT |
| quote: | | If I turn the volume on the amp right up |
right up = comfortable? or right up = too loud? |
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| alleycat |
| Very loud! That's what I was trying to imply when I said that it's not normally a problem, and it's only audible when there is supposed to be silence. Most people would probably call it a nitpick. |
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| AndrewT |
Sounds like -90db below maxiumum power.
Nitpicking is -120db below maximum power. |
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