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
Is there a simple formula that calculates electricity usage/cost of my amp? {ML432} Need to stress the "simple" part. No one mentioned they'd be math in this hobby =]
Lev, your amp's power consumption is specified as 650W in "on" mode (presumably under no signal conditions), 130W in "standby," and 10W in "sleep" mode.

If it is in "on" mode all the time, that computes to 0.65 kilowatts x 24 hours per day x 30 days per month (approx.) = 468 kilowatt-hours per 30 days (yikes!). Multiply that by your kilowatt-hour rate to get the approximate cost per month.

For the other modes, use 0.13 and 0.01, respectively, in place of the 0.65 factor.

Best regards,
-- Al

09-12-11: Rower30
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 don't quite understand why capacitance is of significance. yes, it is true that under the transmission line model, the wire induces signal delays that vary with frequency (i.e. distorts the signal), &c. but the transmission line model generally applied to signals that operate at microwave frequencies, not audio frequencies.

as an example, resistance of audio cords is measured in tens of ohms per kilometer. so let's say that you have a cord with a resistance of 50 ohms/km; for a 1 meter cord, that means that the RC time constant is well into the megahertz range.

what i don't understand is why roll off would even be a consideration in the audio frequency range.
Paperw8, what Rower30 is referring to is the fact that the capacitance of a line level interconnect will interact with the output impedance of the component which drives the cable, forming an RC low pass filter. The "R" corresponds to that output impedance, not to the resistance of the cable.

The bandwidth of that low pass filter can certainly be low enough under some circumstances to have audible consequences, if cable length is long, cable capacitance per unit length is high, and the output impedance of the component driving the cable is high.

For speaker cables, on the other hand, that effect will almost always be insignificant, because of the very low output impedance of the power amplifier. Inductance and resistance may be significant considerations in the case of speaker cables, though, because of their interaction with speaker impedance.

Regards,
-- Al


09-12-11: Rower30
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.

09-12-11: Almarg
Some minor factual corrections to your post:

"3db per octave" should be "6db per octave" (at frequencies above the 3db point).

rower 30 is correct, 3dB/octave is the figure of merit. frequency response charts measure a quantity (typically voltage) as a function of frequency. 3dB represents the point at which the quantity is reduced by a factor of 1/2. 6dB would represent a 3/4 reduction in the quantity. people look at 6dB when referring to power but that applies only to the situation where a voltage (typically an output voltage) is being delivered to a load. in that case, when the voltage is reduced by 1/2, the current is also reduced by 1/2 which means that the power is reduced by 3/4. but that does not apply in the case of a balanced input. in that case, you have a voltage divider, so when there is a 3dB reduction in voltage at a node, there is also a 3dB reduction in power at that node.

take a look at a bryston schematic and you will note that they label the balanced input as corresponding to a 3dB signal reduction. the explanation that i just gave is the reason why.