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    Hum reduction quest - solved !

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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Sun Aug 06, 2017 4:05 pm

    deepee99 wrote:
    LeGrace wrote:One step forward, two back. Today hum is back close to where I started. Sad  Sure hope those adapter plugs or maybe the new shielded cables bring some relief. Really getting tired of this issue.      
    Just use one plug. Otherwise you're just doubling-down on the ground isolation problem.

    Thanks, I'll try just one to start. I have the amps connected into a power strip which then connects into a manual reset gcfi.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Tue Aug 08, 2017 2:56 pm

    Just finished installing my new audiophile quality (ref Siltech 180i`s) IC`s. Hum worsened, back to annoying level. On the flip side audio resolution and detail are both enhanced. But since the hum is part of the audio signal apparently it is also being enhanced. Sure hope those grounding adapters can break the ground loop. Will advise.

    Wondering if the fact I have KT88`s in one amp and KT120`s in the other can be a contributing factor?
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Tue Aug 08, 2017 3:10 pm

    LeGrace wrote:Just finished installing my new audiophile quality (ref Siltech 180i`s) IC`s. Hum worsened, back to annoying level. On the flip side audio resolution and detail are both enhanced. But since the hum is part of the audio signal apparently it is also being enhanced. Sure hope those grounding adapters can break the ground loop. Will advise.

    Wondering if the fact I have KT88`s in one amp and KT120`s in the other can be a contributing factor?
    I shouldn't think so, if you're getting hum on both channels. There's no cross-talk between the amps. Again, plug one amp fully in, and the other through the cheater. If there's a ground-loop that will break it. If it doesn't, use a single cheater on your pre-amp AC plug with both amps plugged straight in. Ground loops are a bitch to trace. Did you route your new ICs the same as your old ones, when the hum went away? Again, keep line-level AC as far away from your ICs as possible or at least cross them at right-angles.
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    jfine

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    Re: Hum reduction quest - solved !

    Post by jfine on Tue Aug 08, 2017 7:05 pm

    Move system to other room in house, or, move system to friends house or run extension cord from friends house just to try and isolate the issue.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Wed Aug 09, 2017 6:10 am

    jfine wrote:Move system to other room in house, or, move system to friends house or run extension cord from friends house just to try and isolate the issue.

    Fingers crossed adapter plugs like you are using will address the issue. Still waiting on delivery.
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    Peter W.

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    Re: Hum reduction quest - solved !

    Post by Peter W. on Wed Aug 09, 2017 2:35 pm

    OK - I suggest you start over from the very beginning. But, first try this:

    WITH EACH AMP:

    a) Remove amp to an isolated location away from any other equipment.
    b) Short the inputs. Connect one regular speaker. Use speaker wires no less than five (5) feet, no more than ten (10) feet long, and kept as straight as possible from the amp.
    c) Plug in, and turn on the amp. Allow a full ten (10) minutes for it to warm up.
    d) Check the bias.

    Is there ANY hum at all? If not, the hum you are getting is induced from another source and/or local to the other location, and/or due to some external interference on the line feeding your main audio location. If so, the problem is internal to the amp(s) in question and must be investigated as such. input and driver tubes being primary suspects. Failed/failing components being secondary, especially if this issue came on slowly.

    Do this with each amp.

    If you are using pre-amp - add this to the front of the procedure above:

    Short the pre-amp inputs.
    Connect the pre-amp out to the amp.
    Allow the pre-amp to warm up for 10 minute before turning on the amp.
    ONE AMP AT A TIME: Test for hum on each pre-amp input position. Run up the volume from 0 - max, slowly!

    If you have a single (mono) patch-cord of decent quality, use it for these tests. Clean all sockets and jacks as well prior to starting the tests, and make sure you are getting good connections not only with the shell, but also the "male" and "female ends". These too can get worn and loose with use. Same deal with the brush and dental-picks.

    Now try both.

    What did you find out?

    First, we must eliminate the easy stuff before searching for more complicated stuff.
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Wed Aug 09, 2017 2:55 pm

    Peter W. wrote:OK - I suggest you start over from the very beginning. But, first try this:

    WITH EACH AMP:

    a) Remove amp to an isolated location away from any other equipment.
    b) Short the inputs. Connect one regular speaker. Use speaker wires no less than five (5) feet, no more than ten (10) feet long, and kept as straight as possible from the amp.
    c) Plug in, and turn on the amp. Allow a full ten (10) minutes for it to warm up.
    d) Check the bias.

    Is there ANY hum at all? If not, the hum you are getting is induced from another source and/or local to the other location, and/or due to some external interference on the line feeding your main audio location. If so, the problem is internal to the amp(s) in question and must be investigated as such. input and driver tubes being primary suspects. Failed/failing components being secondary, especially if this issue came on slowly.

    Do this with each amp.

    If you are using  pre-amp - add this to the front of the procedure above:

    Short the pre-amp inputs.  
    Connect the pre-amp out to the amp.
    Allow the pre-amp to warm up for 10 minute before turning on the amp.
    ONE AMP AT A TIME: Test for hum on each pre-amp input position. Run up the volume from 0 - max, slowly!

    If you have a single (mono) patch-cord of decent quality, use it for these tests. Clean all sockets and jacks as well prior to starting the tests, and make sure you are getting good connections not only with the shell, but also the "male"  and "female ends". These too can get worn and loose with use. Same deal with the brush and dental-picks.

    Now try both.

    What did you find out?

    First, we must eliminate the easy stuff before searching for more complicated stuff.
    Peter, presume you're referring to something like this:
    http://www.ebay.com/itm/RCA-Shielded-Shorting-Plug-Cap-Cover-1-piece-RF-EMI-Noise-Canceling/112171535206?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20160908110712%26meid%3D858dfe3af1664823aca8892c312458d9%26pid%3D100677%26rk%3D1%26rkt%3D17%26sd%3D112171549802&_trksid=p2385738.c100677.m4598
    for shorting RCA inputs. Cheap. I use them on all un-used pre-amp inputs. Might need to crimp them a bit for a tight fit, but they do eliminate extraneous RFI.
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    Peter W.

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    Re: Hum reduction quest - solved !

    Post by Peter W. on Wed Aug 09, 2017 3:02 pm

    Sure. And that is an elegant way of doing it properly. But for the purposes of the test, any jumper is sufficient. I have very narrow alligator clips that stick into the jack and clamp.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Wed Aug 09, 2017 4:59 pm

    With first test (amps segregated) zero hum from either amp. I am familiar with rectifier tube, power tubes, driver tube (small ones) So what do you mean by input tube?

    I still wonder about using different power tubes in the two amps. The amp with the KT120 tubes will draw more power then the one with the KT88's. So currently am having asymmetry situation between amps. Assume rectifier and driver tubes will as a result also be loaded differently. Can this create a slight imbalance between amps leading to formation of a ground loop?

    Additional procedure you mention I do not comprehend. I have many preamp inputs, including balanced inputs. What I can say is hum level is independent of volume position of preamp.

    Also now that I am paying so much attention I now realize situation improve as a function of time. Hum is very noticeable on initial startup and first 20-30 minutes. After 1 hour is getting better, after 2 hours is significantly reduced. When I plug my two amps into common socket it is not the answer, actually it was time factor that was helping.
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    Peter W.

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    Re: Hum reduction quest - solved !

    Post by Peter W. on Wed Aug 09, 2017 5:33 pm

    I will answer at length tomorrow. Too much driving today for a cogent response.

    But, my guess from your last sentence is that you have weak filter caps that are taking their own sweet time to charge. That would explain much, including the on-again/off-again nature of the problem.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Wed Aug 09, 2017 5:42 pm

    Amps are only about 1 year old. How can caps be weak? Also which caps may be implicated?
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    Peter W.

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    Re: Hum reduction quest - solved !

    Post by Peter W. on Wed Aug 09, 2017 5:47 pm

    LeGrace wrote:Amps are only about 1 year old. How can caps be weak? Also which caps may be implicated?

    Main filter caps - and caps is strange beasts, they can fail in days or years.

    • Have you ever run the system with no output tubes?

    • Have you ever run hot (voltage over 120 VAC)?


    Either of which would cause rapid and premature failure.

    More later


    Last edited by Peter W. on Wed Aug 09, 2017 5:53 pm; edited 1 time in total
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Wed Aug 09, 2017 5:49 pm

    Lets follow up tomorrow - thanks...
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    Bob Latino
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    Re: Hum reduction quest - solved !

    Post by Bob Latino on Wed Aug 09, 2017 6:10 pm

    LeGrace wrote:Amps are only about 1 year old. How can caps be weak? Also which caps may be implicated?

    If you have eliminated the front driver tube as a source of the mild hum you have AND the hum you have is on both amps about equally, my guess (which has been mentioned in an earlier posts) is that you have some type of ground loop. Cheater plugs may be illegal to use in Canada but they will lift the M-125's internal ground and in some cases drop the hum level. If you can't find them at a store in Canada, you can probably find them online.

    The definite test for hum in an amp is to pull the input RCA interconnect from the amp and replace it with a shorting plug that grounds the RCA input. You can also use pull the interconnect from your preamp at the preamp and then short between the center pin and the outer shield with the metal blade of a screwdriver on the end of the interconnect you just pulled from the preamp. What you hear from the speaker now is the residual hum level of the amp.

    The key thing that sets up a ground loop is multiple devices in your music system that use a 3 wire cord and that does not refer to the two M-125's. If your preamp, CD player, DAC, computer, turntable etc. has a 3 wire cord, this will set up a ground loop. Many times leaving the M-125's alone and the using a 3 wire cord on the one OTHER device will get rid of the hum.

    Bob
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Wed Aug 09, 2017 6:48 pm

    Input tubes and driver tubes are monikers used somewhat interchangeably as terms here, LeGrace.
    Ignore the distinction.
    They are all, in fact, signal tubes. This is meant to distinguish them from output or power tubes, which exist only as those great big guys on your power amp(s). Each M-125 has two signal tubes in the driver function -- those little guys out front -- and the ST-120 has three of them up front to handle its dual role as a two-channel amp in a single chassis.
    Power tubes are usually not a source of noise: they either go flat or blow up. Signal tubes, which are actually doing the heavy lifting at the critical low values and are therefore much more sensitive to RFI and EFI as a result, are usually, in my experience, the likeliest source of noise.
    But do the ground-swap thing first. Ten bucks says that cures things.




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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Thu Aug 10, 2017 6:55 am

    Still waiting on the plugs, international shipping = must be patient. But I'm less confident now the plugs will do the trick. If it was a ground loop effect, wouldn't the hum level remain constant? Further tests confirm it is indeed routinely dropping in level as a function of amp time on. Suggesting either a tube warming up period factor or maybe as Peter W suggested cap charging rate related. My line voltage does routinely peak up to 121.

    If the plugs disappoint then next step would appear to be ordering a cap tester.

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    Peter W.

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    Re: Hum reduction quest - solved !

    Post by Peter W. on Thu Aug 10, 2017 8:10 am

    OK – I will go into this in some detail. Please forgive me if I get a little bit didactic – hum problems are so common and typically so easy to fix *ONCE the problem is identified* that I get a bit concerned when I see all sorts of speculation without a systematic approach.

    The first question I would ask is whether this is 60 HZ or 120 HZ hum? For the most part, these sorts of issues are 120 HZ, so that is where I am going to focus.

    What we know to-date:
    • When isolated, there is no hum on either amp at any time. Full Stop.
    • When in the system, the hum starts at turn-on, and gradually decreases over time – but the time is longer than normal tube warm-up time (about 40 seconds), and never goes away entirely.

    So, what is the difference between the isolated devices and the complete system? The input device(s). Whether a pre-amp or individual items, or a DAC or whatever.

    So, one-or-another of these devices will either be the culprit, or the first-cause. That is just the way it is. So, what you will need to do is go through each device until either the hum starts or the hum goes away. And, for the purposes of this discussion, patch-cords are considered devices.

    In preparation, you will:
    1. Clean all jacks and sockets.
    2. Tighten the female end of every socket.
    3. Make sure that all patch cords are clean, and only as long as necessary. Sure, some slop is ok, but a 10’ cord to span 18”, no.
    Gradually assemble the system from the speakers-to-the-amps-to-the-inputs. All unused input sockets will be shorted. Report when the hum starts to happen.

    Now, again, I am suspecting filter caps – but NOT on the amps as you have reported that they do not hum at all when isolated. This suggests, strongly, that the pre-amp is a concern. And you have not revealed the nature, age and type of device this might be. But, it would be a simple explanation as to why equal-hum occurs with each amp.

    Aside on Grounding:
    Unless done quite recently – say… later than 1990, and then only if done scrupulously to code, general residential wiring grounds were at best hit-or-miss. Between code-permitted MC cable using the casing as ground, code-permitted one-size-down ground conductors and all sorts of other possibilities, what you see is not always what you get. And why it is that any serious audiophile/phool *WILL* run a dedicated line from the main panel to the system location, and use only it. If one lives in a rental, one will trot out the trusty VOM and find the best receptacle ground available and use that. How? Find the lowest resistance between that ground and the best reference ground you can find – usually a cold-water pipe or radiator supply pipe (sorry if you have PEX – you are SOL for this expedient).

    So, let us know:
    • 60 or 120?
    • When does the hum start when assembling the system?
    • Are you using shorting plugs?
    • What are the ‘other’ components in the system (age and type)?

    I am willing to bet either a Siemens or Telefunken NOS 12AX7 that this is *NOT* a classic “hum loop” unless there is an actual physical defect or broken connection somewhere.

    Best of luck with it.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Thu Aug 10, 2017 8:44 am

    Thanks Peter.

    For preamp using the preouts of a Marantz PM11S1. Mid 90's vintage. Technically I am feeding 4 amps (ea with 3 prong plug) on the same circuit, 2 x M125, the PM11S1, and a powered sub. Signal from the Preamp routes through the sub before going to the M125s.

    As it happens I do have a cold copper water supply line located fairly near my system. When I finally have the adapter plugs should I try running a wire from the plug ground tabs over to it?

    I may be back with more questions, you have given me a lot to chew on. Thanks again.
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    Peter W.

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    Re: Hum reduction quest - solved !

    Post by Peter W. on Thu Aug 10, 2017 9:06 am

    I have been sitting on my fingers around the entire 'adapter plug' discussion. I worked my way through college as an electrician, I have restored three Victorian-era houses and been involved with general construction for over 40 years now. There are no words to express my attitude towards adapter plugs, not even the most vulgar ones.

    As to the copper line - Try this. With a good VOM, measure for any AC or DC voltage between any component on your line and that copper line. As in, measure both in AC and in DC. IF you get any voltage *AT ALL* then your household receptacle ground is suspect.

    Next, use that same VOM in OHMS to test resistance between your household receptacle ground and that copper pipe. It should be as close to zero as your VOM will read. If you get voltage and an ohms reading, the household receptacle ground is "above" the copper pipe ground. And may be a contributor to your issues.

    Run a dedicated line, if you can, using (at least) 12-gauge wire on a conventional circuit breaker - emphatically not an arc-fault device - if permitted. I am OK with a local GFIC device, and I am even OK with a panel-mounted GFIC device, but the cost of the local devices is much less.

    A power-strip (high quality, not $4 HD 4-pack) is a good way to make sure that everything you are using is going to the same line.

    We keep three of these as we have three significant listening venues.

    https://www.zoro.com/tripp-lite-surge-protector-strip-7-outlet-white-tlp712/i/G1796812/

    This is not an endorsement of this product, but to represent the minimum quality acceptable.

    Enjoy!
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    wgallupe

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    Re: Hum reduction quest - solved !

    Post by wgallupe on Thu Aug 10, 2017 10:22 am

    If your system is still hooked up as described in the link below, I would undo all of that and only run the pre outs from the Marantz to the 125s. Nothing else. Then see if the hum goes away.

    http://dynacotubeaudio.forumotion.com/t3276-tube-rolling-for-low-freq-spectrum#29578

    By the way, inserting a subwoofer's crossover into the line level signal path is something I would never do. Just saying...
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Thu Aug 10, 2017 11:02 am

    Signal path is through sub's high pass filter, not its crossover. The high pass is a fixed 80 hz cut off. Could be the high pass cap is a slow poke. Right now the way I have things the sub goes on and off along with the M125's. Maybe I should just be leaving it on.  Or as you suggest bypass entirely, certainly part of a process of elimination exercise.

    Really appreciate all the great suggestions.
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    deepee99

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    Re: Hum reduction quest - solved !

    Post by deepee99 on Thu Aug 10, 2017 11:16 am

    wgallupe wrote:If your system is still hooked up as described in the link below, I would undo all of that and only run the pre outs from the Marantz to the 125s. Nothing else. Then see if the hum goes away.

    http://dynacotubeaudio.forumotion.com/t3276-tube-rolling-for-low-freq-spectrum#29578

    By the way, inserting a subwoofer's crossover into the line level signal path is something I would never do. Just saying...

    WG, I dunno about that. Dick Vandersteen's been doing it for years with great success. But spendy, for sure, and only for his powered subwoofs, which recover the lost low frequency signals with their own EQs. Saves the output tubes from heavy lifting. I don't care for the complexity, but it does work.
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    Peter W.

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    Re: Hum reduction quest - solved !

    Post by Peter W. on Thu Aug 10, 2017 12:31 pm

    LeGrace wrote:Signal path is through sub's high pass filter, not its crossover. The high pass is a fixed 80 hz cut off. Could be the high pass cap is a slow poke. Right now the way I have things the sub goes on and off along with the M125's. Maybe I should just be leaving it on.  Or as you suggest bypass entirely, certainly part of a process of elimination exercise.

    Really appreciate all the great suggestions.

    One question: What are the Marantz PM11S1 on-board amps doing through all of this? Are they isolated (out of circuit, no input and no load)? Are they loaded? Are they receiving signal?
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Thu Aug 10, 2017 12:58 pm

    Peter W. wrote: One question:  What are the Marantz PM11S1 on-board amps doing through all of this? Are they isolated (out of circuit, no input and no load)? Are they loaded? Are they receiving signal?

    They also connect to my Tannoys in a biamp configuration.
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    LeGrace

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    Re: Hum reduction quest - solved !

    Post by LeGrace on Thu Aug 10, 2017 2:10 pm

    Found it! Sub and M125's not playing nice together.

    First step involved migrating the sub off the power bar I'm using for the M125's and plugging it into its own dedicated wall outlet, ie completely isolated from everything else. Secondly I warmed it up for a minimum of three hours to make sure the high pass circuit was fully charged.  

    No more hum, I mean church mouse quiet!! Now I understand why yanking the RCA input before was so effective in getting rid of the the hum. Given the M125s connect directly to the sub removing this connection was breaking the circuit.

    Cant believe how sensitive these systems can be to the way things are hooked up. I never would have suspected this, nor would I have uncovered the problem without all the help! Surprisingly simple solution, but hardly obvious IMO.  This forum rocks!

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