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Why 24/7 warm-up period on amps?

The 24/7 warm-up period on amps seems excessively unsupported. Yes, an amplifier (pre-amp or power amp) will change it's circuit factors as the init heats up since the resistive and capacitive values stabilize...but for months on end? Do we still have a "warm" heart for tubes, that do indeed need to get "hot" to work right?

A capacitor charges up based on it's RC time constant, which is in the SECONDS range, not days. OK, if you add the heat sink area so the heat going out is stabilized I can see maybe an hour or so. My DNA-225 gets HOT in thirty minutes, at which point it's steady state. That even assumes it doesn't have temperature correction circuits to make it more stable, and less subject to change over time.

Break-in periods are hard to judge what people think is happening. Circuit P/N junction temps get hot pretty fast. A mechanical device like a speaker or phono cartridge, sure, they will work-in just like a well used rubber band. But silicone? Factory burn-in is designed to find weak components that degrade outside of SOP ranges, not to "center" their attributes in a normal stable circuit. Did someone forget to add enough heat sink compound to a PNP or NPN transistor, for instance?

Assumming break-in is real, not to be confused with the warm-up period, once it's done it's done. After that it would be warm-up only time. And, warm-up is a simple thermodynamic process. It only takes so long to warm-up and it isn't "days" on end. Maybe hours...if even. Once things are to temp the circuit constants are set. What else is changing? A heat sink is designed to warm-up and hold a delta temperature where the measured performnace is flat. A small amp (pre-amp gain stage) has smaller heat sinks for this reason. Heat and resistance are related, so you have to pick a temp and hold it. You design to THAT attrubute on the component.

Wire conditioning in the amp? ( go here - http://www.angelfire.com/ab3/mjramp/golopid/grain.html) As well as several other sites and textbooks.

The DC path is just that, DC. The magic is the purity of the DC, not the wire moving it around. You either have the right voltage and current capability (wire size)or you don't. Once the amp is on, the wires capacitance hardly matters. PP, PE or Teflon dielectrics only ionizes-tree and fail at break down voltages around impurities, not below that. You do not want to ever ionize the insulation in normal practice.

AC is an interesting issue. The AC complex signal is ALTERNATING differently at each and every frequency point, so the magnetic and electric fileds keep switching with respect to frequency. So the dielectric can not have polarity, or current "direction". The dielectric will not "align" to anything.

Grain structure in copper does not change unless you melt it. It's set when the rod is made. Annealing just resets elongation by improving homogeneous grain alignment, not the grain boundary characteristics since wire is resitive annealed at well below the temp that would fully reform the grain boundary around impurities in the copper. Oh, all modern 9/16" rod copper is made in induction ovens and is essentially OFC grade. All wire is drawn from that rod. Modern copper is also "high conductivity". Again, these terms are throw backs to days gone by with coke furnaces and open air annealing to critical temps where impurities could be picked up, changing the grain boundaries around impurities.

I also notice the people seem to tout TEFLON over Polypropylene or polyethylene dielectrics. Teflon costs more, it is higher temperature capable to 150C-200C (like 80C on polyethylene isn't enough in electronics) but Teflon has a worse dissipation factor and loss tangent. Using Teflon has a more NEGATIVE influence on electricals than olefins. Teflon's velocity of propogation at RF frequencies way above 1MHz is 70% verses 66% for solid olefin dielectrics. But that is at RF. And, you can nitrogen foam either to negate that advantage of Teflon at RF, but NOT Teflon's high price, loss tangent or dissipation factor. Capacitance adjusted Teflon is a poor choice. So the important factors are capacitance, dissipation factor and loss tangent. We can easily fix the velocity of propagation. PE and PP is superior across the board and cheaper (that's probably the problem!).

Good circuits are good circuits. Could you even make a circuit that had electricals parameters that were undefined till it ran, "forever"? Nope, can't be done. Design would then be a game of chance. I don't think that it is. Stabilized junction temps are used to set electrical componenet attributes with respect to temperature. You can design heat sink characteristics to place "hot" components where thet need to be temp wise to meet a circuit requirement. A poorly designed amp that allows thermal run-away under load isn't appropriate and isn't made...for long. There is indeed a circuit junction temp that rather quickly defines the measurable performance of the circuit, and a STABLE delta attribute approximation(s) when a circuit is designed. You know going in what they will be in operation steady state.

So, I hear my speakers and phone stage "break-in. And they don't go backwards once thet are broken-in. They can, in fact, get worse and simply break-down! But my amp sounds fine in short order. The circuit reaches a thermodynamic steady state and we're off to the races. I just can't see a circuit that needs 24/7 "on" period to stabilize...unless it just isn't stable. To me that's a poor design, and one subject to possibly serious load induced instability when the circuit falls outside of the stable design region(s).

I'd sure like to see MEASURED attributes that support 24 /7 warm-ups on sound. I have yet to see any measured data to support this. Show me components used in amps that take MONTHS to reach stady values. I have read PLENTY to support first to third approximation(s) on amplifier circuits ambient thermal temperature stability points. Many circuits are designed to run "cold" and have inverse circuit systems to keep changes due to temp deltas away. This way, you have a more stable circuit at all times. The opposite designis technically UNSTABLE till it gets to temp. This also limits what you can do as it can't blow-up when it is cold BEFORE it gets hot and stable. So the circuit is a compromise.

So just what are the resistive, inductive and capacitive break-in periods on quality components used in a circuit? In God we trust, all else bring data.- unknown
rower30
almarg's avatar
almarg
9,670 posts
 
I would just add to what has been said the thought that if there are in fact mechanisms by which warmup beyond the point of thermal stabilization can produce audibly significant changes, I see no reason to expect those changes to necessarily be for the better. And I would certainly expect both the magnitude and the character of the changes to be dependent on the specific design.

Regards,
-- Al
chazro's avatar
chazro
635 posts
 
OK, howzabout other electronics? My CD player's left on 24/7. I've read that there's benefits to be heard when doing so, I don't hear much of a difference BUT....I've also read that it extends the life of the unit by not powering it on and off all the time. I'd like to hear from the electricians!;)
frogman
7,494 posts
 
Almarg, you beat me to the punch. That is exactly right. I was going to point out that I have owned a couple of amps over the years (Moscode 600, B&K something or other) that after being on for more than 24 hours, exhibited negative effects. The sound would become not just overly dark and thick, but strangely uninvolving (the Moscode in particularly). Nonetheless, others that I have owned really hit their stride when left on for long periods of time.
paperw8
165 posts
 

09-12-11: Almarg
I would just add to what has been said the thought that if there are in fact mechanisms by which warmup beyond the point of thermal stabilization can produce audibly significant changes, I see no reason to expect those changes to necessarily be for the better. And I would certainly expect both the magnitude and the character of the changes to be dependent on the specific design.

a lot (in fact, i suspect the great majority) of high end audio is sold to people who know little about electronics. so in some regards, the most important feature of high end audio products is marketing: because it is through marketing that you make the suggestions that influence consumer perceptions about audio products. you can convince people to believe just about anything with enough suggestion (e.g., a surprisingly large percentage of people still believe that saddam heussein was involved in 9/11). to the extent that people believe that there are sonic benefits from keeping equipment on 24/7, then that's just what they believe. however, other than for the possibility of bad system design, i see no scientifically valid evidence to support such beliefs.

first, while it is true that the electrical characteristics of semiconductor devices does exhibit some thermal dependence, it is also true that semiconductor devices are characterized over a temperature range that goes from well below zero to well above boiling point. so i question whether there really is that significant a difference in the sound of audio electronics over the operating ranges of these devices.

second, even accepting that there might be some audible difference in audio electronics during the "warm up" period (and, btw, the testing methodologies to evaluate this are *highly* unreliable), what really counts is the junction temperatures of the devices, not the ambient temperature that you feel when you touch the heat sink. the junction temperature would rise much more quickly than the ambient temperature, so i would expect the devices to reach their "warm up" within 15 or 20 minutes at most - not over a period of hours.

i would find a more persuasive argument that the sound character of the speaker changed (for largely mechanical reasons) during the course of operation.

as to the concept of "break in": the term, as audiophiles use it, is really a psychological process, not an electrical process. it reflects the time that it takes for you to get used to the sound of a new component. when you install a component in an audio system, it will likely have it's own sonic signature. when you first hear it, you will likely be very sensitive to the differences in sound relative to that to which you may have become accustomed. however, over time you will get used to the sound and will become less sensitive to it. as an experiment, change the loading and/or gain on your phono stage. depending on how much of a change you make you should observe a noticeable difference in sound. if, for example, it sounds too bright at first, over the course of time, and as you get used to the sound, you may perceive that the sound is less bright.

you've just done audiophile "break in" on an existing piece of audio equipment...
rower30 OP
211 posts
 
Well, I see I lot of, "I thinks..." and no real data past typical steady state warm-up (maybe an hour). SS circuits are pretty immune to on/off transients so paying more in electricity than an amp cost (A DNA-225 is over $250.00 to $300.00 a year to run at 135 watts at IDLE!) over it's life seems wasteful.

It seems funny to me everything in audio is better "hot", and no one seems to like it "cold". Circuits like to be COLD! But, you can't keep them COLD! So designers work around that and design to "hot".

Then we get to a PC and enthusiasts we want to cool the heck out of it! Well, an amp is designed to reach a known temp delta and be linear in that range. It shoudn't take "forever" to get there. New KRELL amps run at virtually no power draw at sleep, so they can't be "on" all the time. Not anywhere near RUNNING steady state, anyway. But we all know how good KRELL amps are, right? Or any amp made to sleep.

So past "brreak-in" a concept that shouldn't take too long (find the stuff that won't stabilize at the operating delta when cycled) the forever-on situation seems dubious at best. Yes, I know, we can pretend this is religion and just "believe" it.

I'd bet a bunch of bucks that you can't hear the difference in an amp that's reached steady state temps and one that's been there a year.

I'd like to do a blind test on power cords, too. Power goes all over the county on high voltage lines, step it down at ana xformer, goes through the house in 12-14 AWG ROMEX, through a gazillion dollar power cord that magically realigns the power (how it ever "knows" what it "was" when it left the plant I'll never know) and THEN goes into a CRAPPY IEC outlet, and THEN into the simple wires from the IEC outlet inside the amp to the power DC supply circuit block. Any decent DC block will turn all the AC to pure ripple free DC. If it doesn't, no power cord is going to change that. DC is like "white", there isn't anything there but potential to do work. No phase, no time shift, no frequency variation, just potential energy. Your best lead-in is the ROMEX from the wall! Run that right into your amp. Why make the AC get screwed-up through yet another passive lead? Active leads? Your power supply is agnostic to active leads as it spits out pure DC.

Speaker leads are different, the amp is trying to pump a signal down a load that is trying to force voltage BACK into the amp! Hook a VOM to a speaker and move it and see what you get, a voltage, one that is apposing what's going in the speaker! Speaker leads help, or hurt the amps ability to deal with that back EMF characteristic. It isn't magic, the complex sinusoidal addition of the back EMF can distort the forward EMF and cause cancellations. SHORT leads make this less a complex circuit. So yes, speaker leads are the the MOST "hearable" leads in your system.

High impedance interconnect leads? A precision 25 AWG mini coaxial cable with low capacitance is what you need. Nothing fancy, just good quality. There is (should be) virtually no real current in these leads. The lead is a first order filter (resistor and cap to ground), so the longer it is, the worse the roll off at high frequencies. Keep them short. Special "powered" leads? These isn't enough of an E field to scare a house cat at audio let alone "ionize" the dielectric. And, you better darn not have much of a magnetic field (current induced) or you input impedance is too low and it will swamp out you output amps. Remember, what's on the opposite side of your RCA is UGLY. But we forget what's inside the "box" don't we.

Pre amp to power amp leads need low cap. too. Big ass copper does ZERO at the lengths we're talking about. The attenuation is NOT the problem in leads with no current (E=IR). There is no real voltage drop across the leads. What there is, is an increase in capacitance as the leads get longer (say bye bye to higher frquencies at 3 dB per octave at the filter fo frequency which drops as the leads get longer). So all the gold and silver on earth won't do anthing except take your money. What WILL help, is short LENGTH and low capacitance.

Balance leads have HALF the capacitance as single ended RCA leads. The two wires are about TWICE as far apart, leading to LOW capacitance (about 8 Pf ft verses 17 PF/ ft). So the roll off is half the single ended RCA's roll-off. And, you get NOISE rejection added in for a bonus.

I want to believe all sorts of stuff. But I don't. I can't seem to think I know stuff when I don't. I can hear every thing I said and 'show' you. A steady state amp is a happy amp, be it hot or cold. It just as to be steady state and designed around that temperature.

Do you guys and gals even know how sloppy a typical PNP or NPN "junction" is is inside a transistor? And our beloved SOUND goes through all kinds of these devices? We can't readilly see it, so we pretend all the pretty stuff matters.

So send me data on transistors that explains their phase, amplitude and gain changes with forever-on after steady state and I'll "listen" to that. I won't even get into resistors, which are terribly temperature dependant.

So all the, I just know people can just know. That doesn't help anyone. The one's who really know, and have data they can point to, chim in.
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