Amp warm up

[melmar]

I bought a used B & K ST 1400 amp a couple months ago. One day, I inadvertantly left the amp on for several hours before I noticed it was on. I then turned my pre amp and CD player on, and I thought I was listening to a different amp. The lows were terrific and the highs were nice and smooth. Is this typical of amps? Does it hurt to leave them on instead of turn them off? Thanks.

[Beckman]

I leave my CD player and integrated amp on for about 5-8 hours a day and it is fine. Amplifers have transistors, and diodes which are semiconducting devices. As these devices heat up there resistance decreases and they reach an optimal operating temperature. Depending on the exact design and exact types of transistors and diodes "warm up time" has varying affects on components. My cd player(Cambridge Audio D500SE) sounds better after about 20 minutes when first turned on. My intergrated(Myryad Z140) on the other hand is always on standby mode.

[Mash]

do it. Ooppss! Wrong forum.

Leaving your amp on will raise your electric bill. Unless you amp or whatever is prone to overheating, there is no problem with leaving it on but prudence says that a responsible adult should be there for safety. You don't want to burn the house down.

I do not leave my Futtermans, GAS amp, or Musical Fidelity A2 running except when I have forgotten and left the A2 running. I have never noticed any significant changes in amp performance after a few minutes of warmup.

[bturk667]

I leave all my components on 24/7, except my turntable. Never had a problem in doing so.

[topspeed]

The capacitors in your B&K need time to charge. Think of caps as batteries that store energy. The more energy that is stored, the more they will discharge for brief bursts. I had a ST140 for 15 years and probably had it turned OFF for, oh...30 days total over that time. Why? Because it seemed to take 20-30 minutes to really sound its best and I'm not that patient. If you don't care about the minimal power consumption while it's on standby (from both a financial and moral standpoint), I'd just leave it on.

[skeptic]

The capacitors will charge up in a matter of a fraction of a second to a few seconds.

Amplifiers might change performance when they warm up. It depends on their design. The best amplifiers skillfully take advantage of what is called negative feedback. In negative feedback circuits, the performance becomes dependent on the ratio of the values of reisitors. These do not change and tend to stabalize the performance of amplifiers. The power supplies are well regulated (also using negative feedback) and maintain constant voltage to all of the transistors (or tubes.) The transistors themselves are thermally stabalized by employing a circuit that compensates for their temperature changes. As a result, these types of amplifiers DON'T change much as they warm up. On the other hand, some designers who cannot skillfully use negative feedback which can be a disaster if improperly used, or who have a perverse penchant for avoiding real knowledge and progress and preferring instead to mount a crusade against whatever they don't take up as a religion, might just forgo all negative feedback in amplifier design. In these cases, performance of their equipment will drift all over the place depending on changes in temperature, input voltage, etc.

In fact, because of the inherent reliability of most amplifiers made today and because of their protective circuits designed to shut them down in case of a fault, they can ususally be left on indefinitely without any concern. And in many commercial applications, they are left on for years or even decades at a time only shut down when power distribution systems go down for maintenance or because somebody decides it's time to replace it (just for the hell of it.) However, I'd be more concerned about my loudspeakers because a fault occurring when I am not around might damage them. If they are fused, I'd say no problem. But just in case, it doesn't hurt to turn your amplifier off also. Of course you would have to turn it back on again for several hours before you start to listen again. The solution there is to perhaps wire a switch to disconnect the loudspeakers when the system is not in use (don't try this with tube amps, most don't like being unloaded.

[mtrycrafts]

I bought a used B & K ST 1400 amp a couple months ago. One day, I inadvertantly left the amp on for several hours before I noticed it was on. I then turned my pre amp and CD player on, and I thought I was listening to a different amp. The lows were terrific and the highs were nice and smooth. Is this typical of amps? Does it hurt to leave them on instead of turn them off? Thanks.

Yes, ones perceptions can be dramatic, even if no change has occurred. Tests have shown this time and time again. Interesting why people claim component differences when the same component is presented twice.
Human nature to look for differences, perceive differences when none exists.

The chances are remote or nonexistant that you heard real differences. Perception is different from hearing.

How many times have you asked someone to repeat what they said only to be told nothing was said.

[mtrycrafts]

My cd player(Cambridge Audio D500SE) sounds better after about 20 minutes when first turned on. My intergrated(Myryad Z140) on the other hand is always on standby mode.

How do you test this hypothesis? From memory? Not reliable.

[maxg]

Ever driven a car Mtry? Notice how different it is when the engine is cold as opposed to when it has reached its operating temperature?

Dont tell me - I'm imagining it!!!

well newflash:

Things warm up and their operating characteristics change accordingly.

How long things take to warm up does vary dramatically. A CD player should be just about ready from the get go most of the time, but if it has been especially cold it may take several minutes to get to its proper operating temperature.

SS amps are the same - but hell - dont take my word for it - read the manufacturers instructions - that is what they are there for. If the instructions dont mention anything then by all means use if from the off.

Several amps I have seen go through a kind of boot process that takes a while anyway and wont play until they have finished. Others rely on the operator to be prudent.

My previous Tube amps needed (according to the manual) 20 minutes. The new ones apparently need 5 minutes. Why would they lie?

For my pre-amp the manual says to leave the unit on all the time unless it is not going to be used for an extended period - guess what - that is exactly what I do.

The only caveat I would add to leaving any electrical item on all the time is that you make sure you have some decent circuit breakers in the house in the event that anything serious does go awry.

That applies to refridgerators as much as to amps.

[skeptic]

The only caveat I would add to leaving any electrical item on all the time is that you make sure you have some decent circuit breakers in the house in the event that anything serious does go awry.

That applies to refridgerators as much as to amps.[/QUOTE]

Now how would YOU do that? Fortunately, you don't have to. The National Electrical Code has already done that for you. And the electrician who wired your house and the town building inspector are also on the hook.

Having a car warm up and having an amplifier warm up are entirely different things. With a car, you are circulating oil to lubricate mechanically moving parts that have friction. You are also warming hydraulic fluid that operates your transmission and steering. There are also critical mechanical tolerances which change when temperature changes. When vacuum tubes warm up, their "thermionic emission" characteristics change. That's one reason why we use feedback in tube circuits. When bipolar transistors warm up, they change too. And if they are not thermally stabalized, they can go into what is called "thermal runaway." And then they are dead.

[maxg]

Many readers are not in the US (for example I am in Greece) - so your building codes dont apply - other codes may - its up to you to evaluate them.

As for the different reasons things warm up - true, but many many electrical items do need to warm up (ovens for example - just kidding).

Further, negative feedback is not employed on all amps - most SET amps that I have come across do not use it for a variety of reasons.

I saw your disertation on the benefits of negative feedback - I know a great many people who would disagree with you, at least on sonic grounds. As it happens my amp does employ it - but I have no religious feelings on its benefits or otherwise - I chose the amp on the basis of the way it sounded to me with my speakers - not on its technical specs, which I merely glanced at before buying.

[skeptic]

[QUOTE=maxg]Many readers are not in the US (for example I am in Greece) - so your building codes dont apply - other codes may - its up to you to evaluate them.

I truely feel sorry for you maxg. The National Electrical Code in the United States which is subchapter 72 of the National Fire Code is the product of nearly 100 years of experience that insurance companies and industry have had with electrical safety issues. It changes periodically not only resulting from new technological developments but as the result of tragedies which were due to electrically induced damage to property, injury, or death. We take electrical safety for granted here and I want to thank you for reminding me that not everybody who reads this bb is in the United States. A close friend of mine told me that his family in the Phillipines had lost their home due to an electrical fire. While it still happens occasionally here, it is relatively rare. And when it does, it is almost invariably the result of DIY homeowners or Saturday afternoon handyman types who don't know what they are doing. When I lived in France, I saw things that gave me nightmares.

Negative feedback is not only a very powerful tool in electrical circuit design, we use it in many ways in our everyday lives that we never think about. The first example given by the professor who introduced it to me in school is the example of an individual steering a car. He looks in the direction he wants to go and turns the wheel. His action is driven by the difference between the direction he is going and the direction he wants to go. You can see what happens if the response time between turning the wheel and the change in the direction of the car is too slow (as in steering a large ship) or if turning the steering wheel results in a slight change in direction or drastic change. When you first learn to drive, it takes a while to learn not to overshoot or undershoot steering. (The analogy to no negative feedback would be to drive blindfolded knowing only that a certain number of degrees of turning the steering wheel would result in a certain number of degrees in aiming the car.) It is overshooting or undershooting which creates many problems for desigeners of negative feedback circuits and in the worst case can result in perpetual oscillation trying to correct at every instant by going in exactly the opposite direction with the control that you should be going in to make a true correction. Clearly the mathematics which describe this in detail are very complex--much too complex for wanabee electronics engineers who are really only tinkerers.

[mtrycraft]

Ever driven a car Mtry? Notice how different it is when the engine is cold as opposed to when it has reached its operating temperature?

Dont tell me - I'm imagining it!!!

well newflash:

Things warm up and their operating characteristics change accordingly.

How long things take to warm up does vary dramatically. A CD player should be just about ready from the get go most of the time, but if it has been especially cold it may take several minutes to get to its proper operating temperature.

SS amps are the same - but hell - dont take my word for it - read the manufacturers instructions - that is what they are there for. If the instructions dont mention anything then by all means use if from the off.

Several amps I have seen go through a kind of boot process that takes a while anyway and wont play until they have finished. Others rely on the operator to be prudent.

My previous Tube amps needed (according to the manual) 20 minutes. The new ones apparently need 5 minutes. Why would they lie?

For my pre-amp the manual says to leave the unit on all the time unless it is not going to be used for an extended period - guess what - that is exactly what I do.

The only caveat I would add to leaving any electrical item on all the time is that you make sure you have some decent circuit breakers in the house in the event that anything serious does go awry.

That applies to refridgerators as much as to amps.

Too bad your car analogy is totally different from SS amps. Good try, no cigar

Manufacturers instructions are not in concrete but a safety valve for themselves. Believe every such instruction if you like. That is how they sell you on all this audio nonsense.
Why would one tube need 20 minutes and another 5 minutes? Ask them why. They have no clue.

[skeptic]

Why would one tube need 20 minutes and another 5 minutes? Ask them why. They have no clue.

There is an answer that makes sense. First of all, vacuum tubes have to reach a stable operating temperature. Until they do, their peformance varies considerably. In a well designed amplifier, this should happen within about 30 seconds to a minute or so and five minutes is very conservative so by that time there is virtually no drift due to temperature. In addition, an amplifier which employs a significant degree of properly applied negative feedback and a well regulated power supply will operate stably with gain and performance rock steady. Those which don't because the designer either doesn't know how to use it or has some strange religious aversion to negative feedback will continue to drift all over the place after 5 minutes, 20 minutes, or 20 years. Some of them are NEVER stable.

[mtrycraft]

Those which don't because the designer either doesn't know how to use it or has some strange religious aversion to negative feedback will continue to drift all over the place after 5 minutes, 20 minutes, or 20 years. Some of them are NEVER stable.

So I was right, they have no clue

[maxg]

I spent yesterday reading up on now tubes actually work from a very handy site (http://www.john-a-harper.com/tubes201/#Introduction)

Do we have to now go through a discertation on the different types of tubes used in amps? Surely not.

Suffice to say that Tubes vary in size, type, materials and method of operation. Such differences include, but are not limited to, filaments which are heated directly and indirectly heated tubes. Further different tubes operate at their best at different temperatures (the point at which the electrons are cascading from the cathode to the anode).

Further, in my example I was talking about 2 different types of amp ,with differently sized power supplies, different configurations, capacitors - hell everything really.

With all of the above variations in how long a tube needs to reach its required operating temperature will vary, quite dramatically at times.

Ultimately Mtry - I do owe you a debt of thanks - you made me go and look this up and I learned something.

[mtrycraft]

I spent yesterday reading up on now tubes actually work from a very handy site (http://www.john-a-harper.com/tubes201/#Introduction)

Do we have to now go through a discertation on the different types of tubes used in amps? Surely not.

Suffice to say that Tubes vary in size, type, materials and method of operation. Such differences include, but are not limited to, filaments which are heated directly and indirectly heated tubes. Further different tubes operate at their best at different temperatures (the point at which the electrons are cascading from the cathode to the anode).

Further, in my example I was talking about 2 different types of amp ,with differently sized power supplies, different configurations, capacitors - hell everything really.

With all of the above variations in how long a tube needs to reach its required operating temperature will vary, quite dramatically at times.

Ultimately Mtry - I do owe you a debt of thanks - you made me go and look this up and I learned something.

Unfortunately I was unable to open your link and read what is there so I cannot comment.
I just don't see a 4:1 difference in warm up time. And, I'd be interested in a DBT listeing of the just turned on condition and one that is warmed up, especially in an SS component.

I am glad that you went and looked for answers as too many just accept any opinion if it supports their belief or needs. I have served my purpose

[Beckman]

How do you test this hypothesis? From memory? Not reliable.

You are right. Here is what I will do. Tape a passage from a song comming from the cd player before and after it is warmed up and compare the two. I will post the results as a new thread.

[Mwalsdor_cscc_edu]

In my experience component do need a period to stabilize. This can vary from one product to another and so can the results. Sometimes the change is quite sublte and each user can weight what value the process offers. I leave my digital front end gear on 24/7 as there is no "off" switch and was designed as such. The transport [by the same manufacturer] does have a power switch and is powered down when not in use. As mentioned, tube electronics react differently and I've noticed a more apparent benefit to warmup. Still, unless I'm auditioning or having friends over I'll just flip the switch and after 30 seconds I'm ready to go. Unless I'm using a slow startup rectifier like a Sylvania 5931 (5u4gb) which delays the current flow, leading to a softer start for the plate current flow of the other valves in the system. As they are conducting already when the rectifiers open up, the B+ and therefore the plate current raises slowly. My amp is a direct reactance drive - adjustable bias, zero feedback - 45 / 2a3 driven SET.

MikE

[skeptic]

Vacuum tubes need to come to thermal stability, that is reach a stable operating temperature. That is one criteria for their operating stability. This is sometimes difficult to achieve especially if the equipment is used in an unconditioned environment such as in an unheated manufacturing plant or in places where they might be exposed at times to an external source of heat such as a furnace. Being located near a baseboard radiator in a home might not make much difference. Sitting out in the open as opposed to being placed in a closed cabinet with little ventillation on the other hand might and might even shorten its lifespan. Clearly the voltage applied to the filaments and therefore the current they draw will affect the amount of heat generated and therefore the operating temperature. Most designs do not regulate this voltage especially if the filaments are heated by ac directly off the power transformer. Remember that the wattage is proportional to the square of the voltage (Vsquared/R) so a small change in voltage can create a large change in temperature.

The effective solution is the one most electrical engineers embrace and many vacuum tube loving audiophiles types reject, and that of course is negative feedback. Negative feedback stabalized gain, reduces distortion, and extends frequency response. Changes in operating voltage become much less important. And of course, it takes feedback in the power supply to regulate it and reduce voltage fluctuations further stablizing operating points. In the very early days when vacuum tubes had very little gain, say 20 and were not very reliable, negative feedback hadn't even been invented yet and would have been impractical if it had. However, when tubes were manufactured with gains of 50 or so and became much more reliable and cheaper, negative feedback became a viable design option. Until relatively recently, very few electrical engineers would have considered designing an amplifier without it. But in our modern try anything era, some people have taken a giant step backwards.

[maxg]

the link works fine for me Mtry. Anyone else care to try to let me know if it is only working for me???

I wonder if it is the #intro bit that is the problem?

Try this link instead:

http://www.john-a-harper.com/tubes201/

Maybe that will work better....

[E-Stat]

The effective solution is the one most electrical engineers embrace and many vacuum tube loving audiophiles types reject, and that of course is negative feedback. .

The use of negative feedback is not so much a do-I-use-it-or-do-I-not question so much as to how-much-do-I-use. I favor VTL amps that certainly use negative feedback, but on the order of something less than 20 db vs. 50 db or more in some designs. Say what you will on your opinion as to the efficacy of their designs.

Listening results aside, I have found that the bias of my MB-450s tends to change during first hour or two of operation. For any serious listening, I power them up a couple of hours before listening.

As for SS designs, I rely on the opinion of Nelson Pass, who has designed some rather nice amps over the past three decades. Passlabs warms up their amps for an hour before performing any measurements. If you would like to debate him on the question, he can be reached at diyaudio.com.

rw

[Geoffcin]

I leave my preamp & amp on all the time. The manufacture recommends it. It uses about 100 watts at idle. Much less than my receiver when I'm just watching TV.

One of the things that can happen, that I have not seen posted about here is that if the amp is off for a long time, the capacitors discharge completely, and have to be re-formed. When I got my amp, it had been off for almost three years, and I can tell you that it sounded much better after a week of play, even better after a month. This was not some placebo effect, as I've tested it against other equipment that was in constant use, and the difference between the two setups can easily be tracked.

Quality audio gear allows us to hear the most subtle of differences in sound. It just makes sense that you would be able to hear if it's operating at proper temperature.