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
Let's see...we see a big voltage drop across the power cord, but ignore that TINY little device called a FUSE that EVERYTHING power related goes through!

Wow,I guess a $200.00 Rotel integrated amp would be simply crazy good if we bypass the fuse. Why spend more and risk blowing something nice up with no fuse! The change would be so dramatic that spending more would seem silly.

Seriously, it's hard to look at 10 AWG wire and ignore the worst link in the chain. The fuse IS THE CIRCUIT for all practical purposes unless someone knows something about a series circuit I don't. The voltage drop will pick on the worst component in the chain.
Rower30, I do not blame you for taking that position, and no doubt this is why there are a number of 'HiFi' fuse products now available.

However you can also consider the fuse to be a common denominator in the AC chain, in that you might use the same fuse while auditioning different power cords, and still be able to hear differences between the power cords.

IME, the better the AC wall wiring is (including the outlets), the easier it is to hear the effect of the power cord. That might seem counter-intuitive, but the the wall wiring is in bad shape and has losses of its own that will see the equipment having a lower AC voltage delivered.

I spoke to Richard Brown (Brown Electronics Labs, BEL) many times over the years having owned a (Richard Brown updated) BEL 2002 and two BEL 2001 Power Amplifiers. He steadfastly insisted that his amps should be shut off EVERY time after a listening session because he believed that the startup capacitor charging was critical to proper continued operation of his amplifiers. He felt that restoration to full capacity for critical listening would take less than 20 minutes after a startup. If any one wants to challenge this electrically for whatever reason that's fine, I'm just sharing the personal opinion of one of the most innovative and brilliant amplifier designers of the 20th century.

I've long regretted my sales of these amps. Nothing I've owned since has quite matched them. Not to say there isn't something better but I haven't had the opportunity to experience it yet.

An interesting thread.
"However you can also consider the fuse to be a common denominator in the AC chain, in that you might use the same fuse while auditioning different power cords, and still be able to hear differences between"

I would just LOVE to do a real blind test on this!! I sold stereo for seven years, and we did blind tests all the time after work. Oh what fun, and NO, I was almost always "wrong" on what was what on wire, cords, stands, rock weights, and if my pet rock really loved me.