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  #11  
Old 17th June 2008, 08:15 PM
Richard Richard is offline
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Default Re: Burning in

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Originally Posted by acorn View Post
I would agree with Neal on this one as the most probable cause to be the valves , but sometimes resistors can drift of spec so that the valves work at a different point than expected, when making tests you need to note the cathode and anode voltages each time just to make sure that they tally every time.

Acorn

Hi Acorn,

I did mention that I'd deliberately changed HT by 50V and found it gave no change in frequency response (the sw).

Something is causing a change. It may be the valves, caps, resistors, the wiring or solder joints or the whole lot for all I know .

Rich
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  #12  
Old 17th June 2008, 08:19 PM
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Default Re: Burning in

Nice to see a**e spelt correctly for once
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  #13  
Old 17th June 2008, 08:39 PM
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Default Re: Burning in

Hi Nigel,

Nothing obtuse, just interested in your thoughts . As said, I only know the result as a total from the whole unit and am interested as to which components may be the cause - or perhaps they all are to some extent - or perhaps some offset others etc. I have no particular preconceptions.

What about the solder joints? For Setton to make a whole amp based on no solder joints (everything wire wrapped) makes me think. The sane person might say that although solder is a poor conductor the distance and relative cross sectional area negate this.

As John T mentions though, I too was told a hard wired amp should be able to run before solder is even used. To use solder as glue is bad practice. Maybe solder joints and metal wire/track crystals change during running in.

One of the best interconnects I had (lent it out and it's gone ) was a Pioneer OFC which used welded cable to plug joints. It was audibly superior to almost anything else I've tried. I can't imagine why they'd do that just to make life difficult for themselves.

OFC and long crystal wire is thought by many to be superior. What about linear crystal and joint boundaries? Do they change or improve with use perhaps?

What's the difference between the LRC of 8" of tinned copper stranded wire and a similar length of litz in my tonearm? Nothing much in electrical terms yet it sounds very different.

Why does a carbon film resistor sound different to a metal film? Do they have substantially different L and C?

Why do film caps sound different and also change their sound after a period of burn in? I've seen it suggested a preferred electro chemical "path" is found after a while.

etc etc and not all of it obvious.

Rich
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  #14  
Old 17th June 2008, 08:54 PM
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soulminer soulminer is offline
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Default Re: Burning in

Component drift is normally caused by age and/or heat. Heat drift could easily be checked by running the circuit up again with the scope and SW from the sig gen and spraying individual components (except the valves!!) with freezer spray. This is available from RS, Maplins etc and this is mainly what it is meant for. Compnent fault finding. Could be an interesting experiment Rich and may identify some resistors that may benefit from better/different types. If the freezer spray doesn't do anything, it is either the valves or burn-in (or the fuse is the wrong way round again ).
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  #15  
Old 17th June 2008, 09:11 PM
Richard Richard is offline
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Default Re: Burning in

Hi Lee,

Sorry maybe I made the first post too long in an attempt to supply the details. This is about a permanent change between frequency response checked under similar conditions after several weeks, not heat drift or a fault or anything changing over a short period of time (hours). Many folk report hearing a change after a while but I've never seen it confirmed by test.

Rich
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  #16  
Old 17th June 2008, 09:33 PM
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Default Re: Burning in

I know there is no fault per se Rich. I was just saying that the change in your square wave, that you later re-tweaked using the variable capacitor, could be the result of component drift of the variable capacitor. This could be due to poor quality variable capacitors or the thermal cycling of those capacitors slightly altering them. Maybe replacing the variable with a fixed cap would keep the sw nice and sharp, but your would then lose the benefits of having the variable cap to tweak when you change valves.

Or it could all be down to burn-in of the components...

But what is burn in? Surely it is just the eventual stabilisation of a new component after a period of use and/or thermal cycling? In other words, drift. The value and/or characteristics (mechanical, electrical or chemical) have changed (or drifted) from when the component was initially deployed.

You tweaked the sw back into shape using the variable capacitor, but how do you know it wasn't one of the resistors that had drifted causing the sw deformation. My thoughts were that the freezer spray may have identified any rogue components.
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  #17  
Old 17th June 2008, 09:51 PM
Richard Richard is offline
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Default Re: Burning in

Heat drift was mentioned. I would consider that to be temporary as opposed to a permanent drift away from spec such as is found with old resistors.

Both channels had changed the same amount so possibly unlikey to be a mechanical movement of a cheapo adjustable cap. Pointless making them that poor if they move like that. Good point though and worth noting the slot positions next time.

What is burn in? Good question, perhaps a small permanent/semi permanent drift from initial spec. Or perhaps a change in the way the component conducts electricity after a while of doing so. That may be a burn in without changing the measured component spec.

I don't know if you believe in burn in or not. I do with regard to caps and valves. I heard such a change with newly built Phono but this time found it confirmed on the scope.

Rich
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  #18  
Old 18th June 2008, 03:28 AM
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Baggy Trousers Baggy Trousers is offline
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Default Re: Burning in

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Originally Posted by Richard View Post
. There was a definite "softening" of the sound which coincided with a measurable loss of high frequencies after a month of use. It will be interesting to check again after a while.

Rich
I have long been profoundly suspicious of this "running-in" process. Like a great deal of other apparent nonsense, it is something which I regard as being attendant upon the novelty of valve technology adopted by transistorised people. Messrs Leak, Lowther, Rogers et al never bothered to mention it. If they had conjured the dreadful expression, they would have said "Plug and play - straight out of the box". But, frankly, I just cannot see the urbane Peter Walker saying something as banal as that . . .

However, the elimination of a growing hum problem has required the replacement of all my output valves - I bought two sets. Even to my cloff ears the new 6550s sounded a bit harsh but were unmistakably brighter in the treble. After some three weeks of use, they are sounding very well indeed.

Out of curiosity, I swapped the new valves (ca.110hrs) for the other new ones still in their boxes; by comparison, the (brand) new ones have the harshness originally had by the others and seem a bit brighter. So, perhaps, there is something to this after all. Humble pie tastes disgusting . . All subjective of course as I have no monitoring equipment. Nor do I have the adjustable thingy so will have to live with this gradual deterioration.

However, I remain adamant that the applied cryogenics of leaving the volume control knob in the freezer for a month are unlikely to contribute anything beyond the removal of fingertip warts.

Incidentally, the Tung Sol 6550s lasted for three years and over three thousand hours, so I'm well pleased.

Last edited by Baggy Trousers; 18th June 2008 at 03:39 AM.
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  #19  
Old 18th June 2008, 09:03 AM
Audiognome Audiognome is offline
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Default Re: Burning in

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Originally Posted by soulminer View Post
But what is burn in? Surely it is just the eventual stabilisation of a new component after a period of use and/or thermal cycling? In other words, drift. The value and/or characteristics (mechanical, electrical or chemical) have changed (or drifted) from when the component was initially deployed.
Once again, Lee comes to my rescue, with something far more succint than the two-page rant that I posted and then thought better of. (hopefully, nobody actually had time to read it!)

Simple as that - components stabilise after a bit of thermal cycling. Nothing mysterious, well know effect. Passive components, yes. Valves as well - makes sense to me - and ties in with Baggy's observations also.
But cables? No, that doesn't make sense. In that case, I think it is the listener that is "burning in" !
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  #20  
Old 18th June 2008, 09:57 AM
cjnuk cjnuk is offline
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Default Re: Burning in

At last someone else has said what I have long thought! I have to wear a communication headset in my job, they're not very reliable and I have to use different ones from time to time. Each time I change headsets I notice the different sound quality from the previous one (short term A/B comparison?) and yet in no time at all I completely forget about it and it sounds just like it always has.

Think of the human eye's capability in seeing well in various types of light; we know there are colour temperature differences between say daylight and fluorescent light yet we acclimatise to each instantly.

More the case of the brain burning in than the hardware methinks!
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