| Warm-up Time - Myth or Reality? [message #331136] |
Sun, 06 April 2008 16:38  |
 JGreenslade
Messages: 761
Registered: April 2004
Location: UK |
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In audiophile circles, one often comes across statements suggesting that equipment must be switched on for a couple of hours before it’s at its optimum sonic condition. Obviously, in valve-based equipment, it can take a few minutes before the kit is at its optimum noise / distortion performance because the Cathode takes time to warm up and enable decent flow of electrons to the Plate; however, what about the solid-state world, and is there any point in allowing valve-based gear to warm up for more than a few minutes (bearing in mind that valves, particularly expensive NOS ones, have a finite amount of coating on their filaments, so any time left idle costs)?
I’ve noticed that it often takes a minute-or-so (being generous) for DC offset to stabilise on blocking capacitors (I’m not entirely sure how this affects sound as we’re talking mV of DC, although, by definition, if the cap takes time to stabilise its DC properties, this could suggest other phenomena are taking place which can affect the AC domain).
Considering most audio buffs don’t have temperature / humidity-controlled rooms (or acoustically-treated rooms, but that’s a separate rant), I can well imagine that this could play havoc in terms of establishing consistency between listening to different pieces of kit…
It’s been suggested that certain modern types of electrolytic capacitor need months of use before their electrolyte is at its optimum potential… Is there any truth to this? Could this also be an issue over a period of minutes or hours?
FWIW, I am not one of those guys who think the gear should be permanently powered. Aside from global warming, and taking thermal cycling and the stress from power-up (soft-start circuits should be mandatory IMO) into account, I believe the perils of warm, humid air convection across contacts (particularly pots and faders) outweighs any benefits from having the gear powered 24/7.
What say you? Is there any science here, or is a warm-up period beyond a few minutes an old wives’ tale? Even if there is science, is it likely to affect the sound that much? If a piece of gear has a DC offset fluctuating between +/- 10 mV for a few minutes after switching on, can this affect sound?
Could there be a psychological aspect to this, i.e. one's ears / auditory mechanism conditioning itself to the impending music session? Could it also be that our hearing is most acute when we have most energy, and tends to decay slightly over the day as we get more tired?
Justin
Audio is a vocational affliction
"there is no "homeopathic" effect in bits and bytes." - HansP
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| Re: Warm-up Time - Myth or Reality? [message #331236 is a reply to message #331136 ] |
Mon, 07 April 2008 03:03  |
Bruno Putzeys
Messages: 631
Registered: November 2006
Location: Rotselaar (Belgium) |
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IMHO most "warm up" phenomena are actually listeners getting used to the sound.
That said, I was once demonstrated a highly interesting phenomenon where an electrolytic capacitor was charged after having laid discharged for a while and the result made audible through a sensitive preamp. The capacitor made all sorts of sputtering and buzzing noises that started dying down after some 30 seconds. Curiously, the capacitor only showed this behaviour after having been IR soldered. The same test on a fresh cap produced nothing at all in the way of unwanted noises. The problem was fixed by specifying a through-hole cap in this position.
Also, electrolytics' ESR is temperature dependent. Last time I looked the optimum temperature was around 40º
Apart from something as obvious as the noise phenomenon, it seems unreasonable to expect that equipment performance necessarily improves as it warms up. I'd guess that some would get better and some would get worse. Measurements bear this out. When gear performance changes with time, not all gear changes for the better. Given that few audiophiles report hearing the sound deteriorating during warm-up, we must take the possibility of the listener warming up seriously.
Have more faith, Bambi. The only right way of dealing with headlights is staring them down.
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| Re: Warm-up Time - Myth or Reality? [message #331617 is a reply to message #331136 ] |
Tue, 08 April 2008 10:25 |
John Roberts {JR}
Messages: 105
Registered: April 2004
Location: MS |
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Perhaps this should be looked at as does an exception prove the rule? I have seen a class AB power amplifier where the class A bias circuitry takes time and perhaps heating up to reach acceptable bias that makes an audible difference. I recall one inexpensive guitar amp design using plastic Darlington output devices that was not well behaved and sounded horrible (crossover distortion), especially on cold mornings until it warmed up and biased up.
So yes, I can imagine marginal or sub optimal designs that take a few minutes to get bias right, but that's minutes not days. I guess it's possible for a sloppy design with DOAs or discrete circuitry for some intermediate gain output stage bias to likewise be challenged. If the design is not directly temperature compensated close to the heat generating devices circuit equilibrium could take more time than usual.
IMO any gear that changes audibly and presumably measurably over time like that is poorly designed and not something to brag about. More likely Bruno's theory of allowing time for the listener to adjust to the product more than time for the product to get right.
JR
PS: I have a personal speculation about an unprotected low noise b-e junction being say reverse zenered at turn-on/off and then perhaps self annealing at normal operating current density. If possible this could exhibit the behavior of working better over time. All curves I've seen for current annealing are at elevated current and over time, so this is a huge stretch and only offered as food for thought, not a serious hypothesis.
Resotune at http://circularscience.com/
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| Re: Warm-up Time - Myth or Reality? [message #332567 is a reply to message #331136 ] |
Fri, 11 April 2008 06:39 |
jensenmann
Messages: 30
Registered: April 2007
Location: Karlsruhe, Germany |
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We did a THD+N measurement with a dbx160SL because he sounded really bad right after powering up. It turned out that it needed half an hour to get THD+N down to some acceptable level (0,1%). The value improved with time and was very good after 8 hours (0,00x%).
Jens
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| Re: Warm-up Time - Myth or Reality? [message #332797 is a reply to message #332567 ] |
Fri, 11 April 2008 18:13 |
John Roberts {JR}
Messages: 105
Registered: April 2004
Location: MS |
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| jensenmann wrote on Fri, 11 April 2008 06:39 |
We did a THD+N measurement with a dbx160SL because he sounded really bad right after powering up. It turned out that it needed half an hour to get THD+N down to some acceptable level (0,1%). The value improved with time and was very good after 8 hours (0,00x%).
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Good one... Yes, another circuit with a distortion trim ( the VCAs). In general this would be modest amounts of low order distortion but indeed measurable if not dialed in at a cold start or until sundry devices reach thermal equilibrium.
JR
Resotune at http://circularscience.com/
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| Re: Warm-up Time - Myth or Reality? [message #332821 is a reply to message #332797 ] |
Fri, 11 April 2008 19:55 |
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Tomas Danko
Messages: 3270
Registered: May 2004
Location: Stockholm, Sweden |
Platinum Member |
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| John Roberts {JR} wrote on Sat, 12 April 2008 00:13 |
| jensenmann wrote on Fri, 11 April 2008 06:39 |
We did a THD+N measurement with a dbx160SL because he sounded really bad right after powering up. It turned out that it needed half an hour to get THD+N down to some acceptable level (0,1%). The value improved with time and was very good after 8 hours (0,00x%).
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Good one... Yes, another circuit with a distortion trim ( the VCAs). In general this would be modest amounts of low order distortion but indeed measurable if not dialed in at a cold start or until sundry devices reach thermal equilibrium.
JR
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Only, to some people I wonder if the unit would actually sound better and give them more "vibe" upon boot up, compared to, say, ten hours later...
"T(Z)= (n1+n2*Z^-1+n2*Z^-2)/(1+d1*z^-1+d2*z^-2)" - Mr. Dan Lavry
"Shaw baa laa raaw, sidle' yaa doot in dee splaa" . Mr Shooby Taylor
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| Re: Warm-up Time - Myth or Reality? [message #345133 is a reply to message #337111 ] |
Wed, 28 May 2008 23:25 |
mcsnare
Messages: 683
Registered: April 2004
Location: New York City |
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I'm not sure I believe the cable burn in theory, although in the past I THOUGHT I could hear certain components change over time.
One thing I am sure of, my Krell KSA-250 sounds like ASS for about 15-20 minutes after power up, no bass and fuzzy indistinct highs. Then BAM it just gets right!
Dave
http://www.scotthullmastering.com
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| Re: Warm-up Time - Myth or Reality? [message #345546 is a reply to message #331136 ] |
Fri, 30 May 2008 18:49 |
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Billy Gibbons once asked me to make him an amplifier that sounded like one in the process of turning off...that ultra-distorto sound.
Does this qualify?
Never mind.
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