Vbe and hfe of bjts both change with temperature. Other parameters, too.
FWIW, warm-up and/or break-in doesn't always lead to perceived sonic improvements. For whatever reason, some things manage to sound better, while others end up seemingly sounding worse.
But this area is highly subjective, and YMMV.
regards, jonathan carr
FWIW, warm-up and/or break-in doesn't always lead to perceived sonic improvements. For whatever reason, some things manage to sound better, while others end up seemingly sounding worse.
But this area is highly subjective, and YMMV.
regards, jonathan carr
right on the money
my understanding is that warm-up time is applicable to some amps some of the time, but not to all amps all of the time, its a case to case basis, depends on what amp you have, because i never really noticed this, i liked ss amps simply because i can have my music in a jiffy....
my understanding is that warm-up time is applicable to some amps some of the time, but not to all amps all of the time, its a case to case basis, depends on what amp you have, because i never really noticed this, i liked ss amps simply because i can have my music in a jiffy....
I think trying to force an amp into it's thermal operating range defeat's the purpose of letting it get thier at it's own pace.
The Heatsink is as much as a device stabilizer as it is for dispersing heat. If all the devices are working in the desired temperature range, they will sound more harmonious. Once at operating temperature thier is a tendancy for the device to operate at the Heatsink temperature, it is called equillibrium.
The larger the Heatsinks the greater and more effective equillibrium has over the devices.
Leaving the devices running constantly may be enviromentally wasteful but it does prevent thermal cycling, which is what causes fractures around the junctions to form and eventually spread to the surface and burst as a result of arcing. I hear that can really affect the sound!!
It has been stated many times that device matching is implemented to get all the devices performing in like characteristics, but that is not the end of the process, just the beginning.
Regards
Anthony
The Heatsink is as much as a device stabilizer as it is for dispersing heat. If all the devices are working in the desired temperature range, they will sound more harmonious. Once at operating temperature thier is a tendancy for the device to operate at the Heatsink temperature, it is called equillibrium.
The larger the Heatsinks the greater and more effective equillibrium has over the devices.
Leaving the devices running constantly may be enviromentally wasteful but it does prevent thermal cycling, which is what causes fractures around the junctions to form and eventually spread to the surface and burst as a result of arcing. I hear that can really affect the sound!!
It has been stated many times that device matching is implemented to get all the devices performing in like characteristics, but that is not the end of the process, just the beginning.
Regards
Anthony
That amplifiers seem to sound better after properly heated up in seems to be a fact(?). The explanations sofar I have seen in this thread are:
-Time needed by passive parts to set.
-temperature effects on active components which operate differently at different temperatures.
-Time needed by a heatsink to establish a stable working temperature.
Checking some small transistor databooks I found nearly nothing on temperature effects. Everyone specifies at T amb. 25 deg.C. implicating that values change with temperature.
In high power devices mostly the Safe Operating Area is worth to spend some paper on.
I found one remark In an old Hitachi Power MOSFET book remarkable. It describes some 2000hr stress testing in which some parameters change permanently " a little in the beginning". This might influence the first working hours of an amplifier but should settle in the long run.
Hmm-I am not satisfied with what I heard and found sofar.
When we design we take great care in selecting parts, doing our calculations etc. We strive for the best. But we seem to accept that during the first hour every time we switch on we are not in control of our ultimate design goal.Luckily the sounds improves...
Or there is still a lot of audio myth forming going on, and the remarks of Jonathan Carr are very true that the sound can get worse too, or we have go back to the drawing board.
Ward
-Time needed by passive parts to set.
-temperature effects on active components which operate differently at different temperatures.
-Time needed by a heatsink to establish a stable working temperature.
Checking some small transistor databooks I found nearly nothing on temperature effects. Everyone specifies at T amb. 25 deg.C. implicating that values change with temperature.
In high power devices mostly the Safe Operating Area is worth to spend some paper on.
I found one remark In an old Hitachi Power MOSFET book remarkable. It describes some 2000hr stress testing in which some parameters change permanently " a little in the beginning". This might influence the first working hours of an amplifier but should settle in the long run.
Hmm-I am not satisfied with what I heard and found sofar.When we design we take great care in selecting parts, doing our calculations etc. We strive for the best. But we seem to accept that during the first hour every time we switch on we are not in control of our ultimate design goal.Luckily the sounds improves...
Or there is still a lot of audio myth forming going on, and the remarks of Jonathan Carr are very true that the sound can get worse too, or we have go back to the drawing board.
Ward
I still vote for imperfecr thermal tracking as the simplest explanation. Take a look at Self's section on schemes to improve tracking. Even if the sensing device can theoretically provide exact inverse feedback there is still a time lag which depends on physical construction of the amp. I haven't seen the inside of single commercial example that looks like they employ anythiong close to Self's suggestions although I see DIY examples here pretty routinely. Having emoplyed these myself, I know that the assembly is a tad fiddly and it doesn't look like it lends itself to auto-insertion. And, of cource, if the amp is based on an IC -- who knows . . .
IMHO manufacturers design a part to do a specific task within a given set of parameters and allow at least a 50% factor for error. They publish thier perfomance data on this narrow criteria, market the device and move on. These manufactures almost never investigate the maximum performance criteria under a multitude of conditions as it is just to expensive for them. It is the finished goods developers that take these parts and start playing with them, Mr. Pass closely matches his FET's for the best possible outcome. IRF did not do this, they may not have anticipated this avenue of development, nor do they care. If they did they would have made matched sets available right from the factory, but they did not, it was not part of thier design criteria, it does not appear in thier engineering notes. Does this mean that Mr. Pass is not on a valid developement path because IRF did not validate the process, certainly not.
Pushing the limits of Engineered products is a big part of DIY, using the same parts but making it better, well that's just too cool for words.
Anthony
Pushing the limits of Engineered products is a big part of DIY, using the same parts but making it better, well that's just too cool for words.
Anthony
EDUM said:
Although I admit that many transistor datasheets are almost
a joke nowadays, many do in fact provide graphs for how
certain parameters vary with temperature. Besides, most of
the effects should be possible to derive using some elementary
semiconductor theory. I guess the main problem there is
that the thermal impedance is seldom published in the datasheets.
Varying parameters.
IMHO it might not be necessary to have rock solid dc operating point stability. If it ( operating point ) is under control and varys SLOWLY within limits , it should not affect the sound. One might be going overboard by trying to pin the dc operating point to a fixed level.
Might be a waste of time and components and might not worth it.
Considering that even a persons two ears do not have identical characteristics , we could accomodate some variations in systems that we work with. Gives us more time to listen to the music !
Cheers.
IMHO it might not be necessary to have rock solid dc operating point stability. If it ( operating point ) is under control and varys SLOWLY within limits , it should not affect the sound. One might be going overboard by trying to pin the dc operating point to a fixed level.
Might be a waste of time and components and might not worth it.
Considering that even a persons two ears do not have identical characteristics , we could accomodate some variations in systems that we work with. Gives us more time to listen to the music !
Cheers.
amp warm-up time
hi everybody & good day,
hello joan2, its good you had put up this topic.
i like the summary of edum of all the responses but i dont seem to see any general agreement why the amp should be warmed up.
well my experience with my amp is this; as the what the maker of my amp recommended i should warm up the amp for about 15 to 30 mins. i followed it coz who am i to question their recommendation and i like what i hear. but curiousity overcame so i tried a different set on.
1. set on the amp and listen to the music - sounded good
2. set on the amp as recommended - sounded better
3. set on the amp for 1 hour - sounded much better
4. set on the amp for 2 hours - no difference with #3
as my standard practice i warm it up for at least 1 hr. reason i dont know.
i tried having my amp on for 24 hrs - no difference with 1 hr. warm-up time. i went even further, i had it on for 1 week coz some of my friends say it would sound better - no difference except my electric bill, it was like installing another unit of air-con and have it on for 24hrs.
hi everybody & good day,hello joan2, its good you had put up this topic.
i like the summary of edum of all the responses but i dont seem to see any general agreement why the amp should be warmed up.
well my experience with my amp is this; as the what the maker of my amp recommended i should warm up the amp for about 15 to 30 mins. i followed it coz who am i to question their recommendation and i like what i hear. but curiousity overcame so i tried a different set on.
1. set on the amp and listen to the music - sounded good
2. set on the amp as recommended - sounded better
3. set on the amp for 1 hour - sounded much better
4. set on the amp for 2 hours - no difference with #3
as my standard practice i warm it up for at least 1 hr. reason i dont know.
i tried having my amp on for 24 hrs - no difference with 1 hr. warm-up time. i went even further, i had it on for 1 week coz some of my friends say it would sound better - no difference except my electric bill, it was like installing another unit of air-con and have it on for 24hrs.
Hi all,
I just thought I share my ideas and experiences about the topic.
I have an amplifier which has a negative feedback, and in this feedback loop an electric capacitor is used. For phase accuracy the frequency break point is very low and it is achieved by a relative large capacitor, say 1000uF. This topology is not differential pair based, thus those capacitors have voltages accross them (One connection is indeed at the voltage level of the output, which is almost zero, but the other one connects to the input stage in a way, that it has an operating point other than zero...) So this capacitor charges up, but it takes time because of its value. This time is about 10 minutes. Till then the phase and frequency response of the amplifier is not at the designed level, it can be measured. (Question: who knows what this means in case of those feedback electrics not even having any voltage accross them?)
So this is obvious in my case.
I have also read somewhere that bjts are following thermal signals up to 10 KHz. It means that an audio signal can modulate the bjts physical paramaters if they do not have enough thermal inertia. Reaching this inertia can take some time beacuse bjt based circuits operate most time with low currents and they are small (Don't forget that what you see is the package, not the actual semicanductor which is much-much tinier). Some say that is one point why tubes sound better. They are physically larger and they are hot. And of course it is true for class A amps as well (they are hot), but do not forget that even class A amps have usually driver stages operating with a few milliampers.
But latter part of my letter is not based on any experience I had, I just read about it...
bt
I just thought I share my ideas and experiences about the topic.
I have an amplifier which has a negative feedback, and in this feedback loop an electric capacitor is used. For phase accuracy the frequency break point is very low and it is achieved by a relative large capacitor, say 1000uF. This topology is not differential pair based, thus those capacitors have voltages accross them (One connection is indeed at the voltage level of the output, which is almost zero, but the other one connects to the input stage in a way, that it has an operating point other than zero...) So this capacitor charges up, but it takes time because of its value. This time is about 10 minutes. Till then the phase and frequency response of the amplifier is not at the designed level, it can be measured. (Question: who knows what this means in case of those feedback electrics not even having any voltage accross them?)
So this is obvious in my case.
I have also read somewhere that bjts are following thermal signals up to 10 KHz. It means that an audio signal can modulate the bjts physical paramaters if they do not have enough thermal inertia. Reaching this inertia can take some time beacuse bjt based circuits operate most time with low currents and they are small (Don't forget that what you see is the package, not the actual semicanductor which is much-much tinier). Some say that is one point why tubes sound better. They are physically larger and they are hot. And of course it is true for class A amps as well (they are hot), but do not forget that even class A amps have usually driver stages operating with a few milliampers.
But latter part of my letter is not based on any experience I had, I just read about it...
bt
warming up!
We have to do with at least two different things!
Almost all manucturers of electrolytic capacitors specify that the capacitor should be "formatted" if it's used after a period of 6 months upon leaving the production plant. This formatting preferably is done by connecting the capacitor to DC-source with a small loading current. On big capacitors (used in the power supply) there's a date of production stamped on it for this reason.
In practice this is impossible to do so when one buys his equipment in a store. The only thing to do then is leave it switched on for at least 4 weeks. This goes as well for solid state as for tube amps.
Quite another thing is the settling of the chip temperature in semiconductors. Upon switch-on a transistor needs hours in order to stabilize to it's optimum point of functioning (not so with tubes!).
Class-A amplifiers mostly need between 1 and 3 hours of warming up before you can enjoy their musical quality.
My current pre-amp with tubes and solid state power amps have been switched on for more then 12 years without any noticeable degradation of their sonic qualities!
Switching off indeed shortens the lifetime of electronic equiupment.
We have to do with at least two different things!
Almost all manucturers of electrolytic capacitors specify that the capacitor should be "formatted" if it's used after a period of 6 months upon leaving the production plant. This formatting preferably is done by connecting the capacitor to DC-source with a small loading current. On big capacitors (used in the power supply) there's a date of production stamped on it for this reason.
In practice this is impossible to do so when one buys his equipment in a store. The only thing to do then is leave it switched on for at least 4 weeks. This goes as well for solid state as for tube amps.
Quite another thing is the settling of the chip temperature in semiconductors. Upon switch-on a transistor needs hours in order to stabilize to it's optimum point of functioning (not so with tubes!).
Class-A amplifiers mostly need between 1 and 3 hours of warming up before you can enjoy their musical quality.
My current pre-amp with tubes and solid state power amps have been switched on for more then 12 years without any noticeable degradation of their sonic qualities!
Switching off indeed shortens the lifetime of electronic equiupment.
Re: warming up!
Is that for power bjts? I find it hard to believe given how much thermal mass they have.
first of all, there is no assurance that a transistor will reach its optimum point after hours, if such a point exists in the first place. So you can get into a situation where warming up can heard sound quality.
2ndly, there is no assurance that rearching this optimum point will give you audiable diffeence. It is entirely possible that the amp will just sound the same. and I think it is likely it will given the amount of feedback and small temperature effect on SS devices.
Banfi T. said:
Is that for power bjts? I find it hard to believe given how much thermal mass they have.
johnrtd said:
first of all, there is no assurance that a transistor will reach its optimum point after hours, if such a point exists in the first place. So you can get into a situation where warming up can heard sound quality.
2ndly, there is no assurance that rearching this optimum point will give you audiable diffeence. It is entirely possible that the amp will just sound the same. and I think it is likely it will given the amount of feedback and small temperature effect on SS devices.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.