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Burn-in revisited

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Graham Slee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Topic: Burn-in revisited
    Posted: 08 Jul 2009 at 11:12pm
Unfortunately all audio electronics have a burn-in time and I for one wish they didn't...

It's mainly a complex function of capacitors, especially electrolytic types which audio circuits cannot get away with not having. Initially (as data sheets describe) leakage and dissipation factors are high but after some time of the equipment being switched on leakage diminishes to a fraction of its initial state and the dissipation factor adopts its specified perecentage. The rate at which this happens depends on where the capacitor is in the circuit: if it is straight across the power supply the time involved can be pretty-short, but if it's in a potential divider with a resistance much higher than say 1k or the voltage at that point in a circuit is substantially lower than the capacitor's rated voltage (which often it needs be to obtain the lowest DF), that takes substantially longer. If one cap is seen as a falling curve on a graph, then many are seen as superimposed falling curves - like a downward staircase - once all have adopted their end values regarding leakage and DF, it's burnt-in - but that can be weeks.

Further to that, metal film resistors (best for audio in my opinion) are known to take months, but that applies to almost all audio gear and this effect is much less noticeable.

An RIAA stage cannot avoid large numbers of capacitors because they're needed for frequency correction of the replay curve. These however are film capacitors and of smaller value and will adopt their final values sooner, but the twist to the tale is the RIAA stage also has electrolytics at places where there are potential dividers having considerably higher resistances than 1k.

The phono stage will unfortunately take a bit longer - about 3 weeks.

The reason why we advise the user to leave equipment powered on is to avoid going through this process over and over, because as soon as the equipment is powered down capacitors loose their charge (but should not completely revert to their as-new state). Because our designs ensure electrolytics always have a DC polarising voltage across them it can be seen that a signal isn't necessary during burn-in (or is it?)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mikebailey61 Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jul 2009 at 9:27am
Thanks for the reply Graham and for putting this up for everyone. I guess then that it's not just a case of allowing a burn-in period with any audio product but to keep it smouldering  too!
I'm not sure about the necessity of a signal during burn-in either. I would guess that driving everything to its quiescent state and holding it there may be good enough and that any additional ac burn-in can be ignored. On the other hand ....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pompeyexile Quote  Post ReplyReply Direct Link To This Post Posted: 12 Jul 2009 at 3:40pm
Graham I now see the reason to keep equipment fired up but  I posed a question ages ago on the previous burn in thread but never got an answer so can I have your advise on this?
 
My Musical Fidelity NuVista CD player has valves inside and naturally they have a limited life-span which I know should be quite a few hours worth of listening. I rang Musical Fidelity who said there was no need to keep the CD player fired up as the valves needed only about twenty minutes to warm up; still they are considering only the valves and not the rest of the electronics. However, will in your very knowledgeable opinion keeping the CD player switched on still benefit it's sound as much considering it uses valves? I assume the sonic signature of the CD player changes from cold valves to fully warmed up ones.
 
The replacement valves will cost me about £100 according to MF (and will no doubt rise year on year so I suppose I really should get a spare set in) and I know I have to weigh up if the improvement in sound will be worth the reduced valve life, but your opinion/advice would be appreciated.
 
 
 
 
 
 
 
 
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Graham Slee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 12 Jul 2009 at 5:06pm
It is possible that the product has been "adjusted" to sound best within a matter of minutes from switch on, let me explain...

Some circuits can actually start to sound worse after being on a long time, and indeed, capacitors are mainly to blame. A valve or other device (semiconductors) should not need hundreds of hours to "burn-in", however passive components, which all circuits have to have, do require hundreds of hours to reach their optimum values. In the case of a metal film resistor for its temperature coeffiecient to stabilise, up to 4 thousand hours ellapse.

Having designed on-all-the-time circuits (the type switched on for life in radio studios - not forgetting the transmitter audio gear which can't really be turned off apart from when another piece is put in circuit while the first one goes for service/repair) I noticed things do change - the question is what things and by what mechanism?

I am currently experimenting with differing voltages of electrolytics from general purpose to exotic audio versions. One expert, Walt Jung reckons that the lowest disipation factor sounds best (he is what I'd call a reputable expert) but I find that on-all-the-time their sound deteriorates where those of high disipation factors don't so readily (it is obviously important to me to find the parts that have the required staying power).

It is very difficult to answer a question about another manufacturer's product - it would be good if they could do so themselves but I either had it from you or heard it somewhere else that MF shrugged it off as a failure function of things being switched on and off - unfortunately other products than audio that use the same type of components demonstrate the statement is false - I have not only made audio in this life but a number of control systems which do one heck of a lot of switching without prematurely breaking.

The best I can really say is this: I once attended a municipal theatre play, and being careful with the pennies the sound system was switched on just prior to the start of the performance - it sounded dire!

About half way through the dialogue became intelligable, and by the end (after the interlude in which I heard the speakers pop indicating they'd turned it off again) the sound had just started to become enjoyable.

When a band goes on tour or in the west-end theatre a sound system must be at its optimum full time - very little differs from the radio studio or recording studio - technicians don't go round turning things off to save a few pennies - if they did I'm sure somebody would start singing on stage without a sound and the technician would be picking up his P45 shortly afterwards.

What I envisage is that by leaving your MF CD on all the time is that the passives will eventually reach their optimum but the valves will have passed theirs, maybe reaching a plateau somewhere in between.

Sorry I could not be of better help but valves are something I learnt about but don't design with.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote cattle prod Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2009 at 10:52am
Sorry if this is a dumb question - but how do I burn-in my newly built Novo kit and the Grado RS-2 I will be using with it?

Actually, all my kit is pretty new (less than 6 months old) and gets far less use than I would like, mrs Cow Prod is not a fan of my music - hence the purchase of 'cans'.

The cans have been running for the past 12 hours continuously off my iMac running a 'play-list' via iTunes - is that the best way to do this but I can't do this with the CD player.

The Novo needs 400 hours of burn-in - is that correct? How should it be done? Thanks in advance.
cheers

Ian
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Graham Slee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2009 at 11:20am
The way amplifiers "burn-in" is through being left on. With some whacko DC coupled amps that could be bad advice because having worked in the industry... Censored (I can say no more because I value the few quid [GBP] I have)

You're safe as far as not having any damaging DC on the output of our gear (if you built it right and I have no doubt you did).

Headphones are a little different (as are all transducers) - they get their power as the signal driving them so need some signal to "free-up" the new "tightness" of the moving parts. A little warmth in the form of an airing cupboard or similar (a problem for me as my matchbox doesn't have an airing cupboard) also helps the modern plastics used in headphones "relax" from the deformations the moulding processes can leave behind.

After a few weeks of such treatment things will sound noticeably different and more enjoyable from when new.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mrarroyo Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2009 at 4:27pm
I have found that with some gear it is good to expose the components to on/off cycles while doing the initial burn in. By this I mean to leave the gear on for 20-22 hours of every day w/ the remaining 2-4 hours the unit off. Repeat this cycle until you achieve 200 hours of actual burn in and for most gear that should be sufficient. Of course there are a few items which require far more burn in, ...
Miguel
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