Re: warming up!
That is not quite the formatting procedure I have read about
in several places. Rather you should slowly raise the voltage
over them up to the max rating and then slowly down again.
This is what they do at the factory, as far as I understand, but
there they go up to some 25 - 50% over the rated voltage.
As i understand it, you cannot properly format them in situ by
just powering the equipment, and the time it is powered won't
matter either. Electrolytics dry out faster when powered though,
so leaving your equipment on 24/7 is not good for them. Take
some time to check a few datasheets. You'll be surprised how
much the lifespan differs between brands and models. Then
think about how many hours there are in a year.
johnrtd said:
That is not quite the formatting procedure I have read about
in several places. Rather you should slowly raise the voltage
over them up to the max rating and then slowly down again.
This is what they do at the factory, as far as I understand, but
there they go up to some 25 - 50% over the rated voltage.
As i understand it, you cannot properly format them in situ by
just powering the equipment, and the time it is powered won't
matter either. Electrolytics dry out faster when powered though,
so leaving your equipment on 24/7 is not good for them. Take
some time to check a few datasheets. You'll be surprised how
much the lifespan differs between brands and models. Then
think about how many hours there are in a year.
Re: Re: warming up!
In principle all stages, without the output one, always function in class-A. What happens is that the chip warms up, this effects the collector current going up a bit. Thereafter the circuit tries to stabilize by decreasing the base current (we don't want the "avalanche effect of the sixties!), collector current goes down and so the chip temperature. Then the collector voltage goes up and so does the base current, warming up again! It really takes hours.
What we "hear" subjectively is quite odd: with warming up abd cooling down the dimensions of the chip vary. So the capacitances vary while warming up and phase will shift. So you have an amplifier with varying "character" during warming up.
The power transistors will suffer from the same effect. In Class-A power amps the phase shifting due to the amplitude of the signal, is relatively small.
Phase shifting causes (or is) a timing problem. Did you know that the human brain "measures" the length of a sine wave (in time!) in order to recognize the pitch?
And yes I know amplifiers which seem to produce a constant sound quality whether after switch-on or after hours. Those ones will never get into my set up!
millwood said:
In principle all stages, without the output one, always function in class-A. What happens is that the chip warms up, this effects the collector current going up a bit. Thereafter the circuit tries to stabilize by decreasing the base current (we don't want the "avalanche effect of the sixties!), collector current goes down and so the chip temperature. Then the collector voltage goes up and so does the base current, warming up again! It really takes hours.
What we "hear" subjectively is quite odd: with warming up abd cooling down the dimensions of the chip vary. So the capacitances vary while warming up and phase will shift. So you have an amplifier with varying "character" during warming up.
The power transistors will suffer from the same effect. In Class-A power amps the phase shifting due to the amplitude of the signal, is relatively small.
Phase shifting causes (or is) a timing problem. Did you know that the human brain "measures" the length of a sine wave (in time!) in order to recognize the pitch?
And yes I know amplifiers which seem to produce a constant sound quality whether after switch-on or after hours. Those ones will never get into my set up!
No, I didn't know that and furthermore I don't believe it really does it like that. Frequency is measured by the resonant behaviour of the basilar membrane and the subsequent excitation of the respective hair cell(s).
But I can still agree with you that temporal (i.e. phase) behaviour is important. The inter-aural delay is used to determine the direction of a sound source. The delay between the various spectral parts, generated by a single sound source, is used to determine the size of said source.
Regards
Charles
Re: warming up!
"drying out" of electrolitical caps is a problem (if the wrong types are used).
Datasheets of various types revealed guaranteed working life between 1,000 hours @ 85 deg C and 12,000 hrs @ 85 deg's. Used at 40 deg C working life increased by somewhat factor 4. But 4,000 hrs is still not a long time in a 24/7 setup. (just over 24 days).
So life-expectancy is depending most-likely on operating temp and type of capacitor.
Cooling down/heating up introduces stress on soldering bonds. Leaving an amp (or any device) on removes this fail-factor.
johnrtd said:
"drying out" of electrolitical caps is a problem (if the wrong types are used).
Datasheets of various types revealed guaranteed working life between 1,000 hours @ 85 deg C and 12,000 hrs @ 85 deg's. Used at 40 deg C working life increased by somewhat factor 4. But 4,000 hrs is still not a long time in a 24/7 setup. (just over 24 days).
So life-expectancy is depending most-likely on operating temp and type of capacitor.
Cooling down/heating up introduces stress on soldering bonds. Leaving an amp (or any device) on removes this fail-factor.
If the bias-stabilising electronic-thermal-thermal-electronic feedback loops were designed correctly then most amps would settle thermically without overshoot or unreasonably high delays.
But that's not easily achievable not even with Self's proposals - simply because you have to model the whole loop correctly, which isn't an easy task.
OTOH why bother to stabilise the bias current via such a complicated feedback loop when it could be done purely electronically ?
Regards
Charles
phase_accurate said:
Most electronic engineers don't know about research on human perception. Also in those circles few is known about the actual functioning of the human body. Easy thing is to believe that the inner ear detects frequency and to measure electronic behaviour of equipment the easy way.
In 1978 in the US and the Netherlands for the first time it was possible to measure the action in the inner ear in a living person. Odd thing is that is was found that when a single frequency sine wave was used a group of hairs on the membrane was actived (firing electrons into the brain). So the assumption that we recognize pitch with our hearing system is a false one, it's a brain function (black box).
Perception research led to the finding that we actually measure time in our head (the length of a single sine wave is compared with the second one and then detected!).
Proof of the latter is easy, if you're interested I could provide you with a method for that.
Now when perception (even partly) is based on "time" measurement we have a problem in electronics. Almost everything we use shifts time when amplitude shifts. Worst thing are "cold" transistors. Next are ceramics. But there's also a delay in capacitors. Now when, for instance, "overall NFB" is used our brain has a problem. This is corrected automatically in our brain but at the cost of some energy. Think about it.
Indeed direction of sound sources has to do with the interaction of two ears (correlation), but also the outer part of the ear acts as a filter which tells us whether a sound is coming from behind or front or above us.
More is to be found in the JASA journal for instance.
Hi John
So what do you assume the frequency selective behaviour of the basilar membrane is intended for ?
How do you think the brain would be able to measure the frequencies of multpiple tones at the same time ??? Try to do it on a scope you may see how difficult it is to determine the beginnings/ends of all those sinusoids.
And how do you think our hearing system could recognise spectral content ?
Yes please ?
I agree on that but not relating to the detection of pitch since a pure delay won't change the frequency of a signal. The MODULATION of phase would indeed change the frequency of a signal (but this would happen independantly of HOW we perceive pitch).
But with the termal time constants of an amp and the small phase errors due to this effects this would be smaller by some orders of magnitude than the FM distortions generated by speakers for instance.
There are indeed errors introduced by phase anomalies but usually not even the most crappy amp isn't as bad as the best speakers in this respect !
I am fully aware that the HRTF is also used to perceive direction (some two-channel "surroud" systems make use of this), I was just simplyfying.
Regards
Charles
So what do you assume the frequency selective behaviour of the basilar membrane is intended for ?
How do you think the brain would be able to measure the frequencies of multpiple tones at the same time ??? Try to do it on a scope you may see how difficult it is to determine the beginnings/ends of all those sinusoids.
And how do you think our hearing system could recognise spectral content ?
Yes please ?
I agree on that but not relating to the detection of pitch since a pure delay won't change the frequency of a signal. The MODULATION of phase would indeed change the frequency of a signal (but this would happen independantly of HOW we perceive pitch).
But with the termal time constants of an amp and the small phase errors due to this effects this would be smaller by some orders of magnitude than the FM distortions generated by speakers for instance.
There are indeed errors introduced by phase anomalies but usually not even the most crappy amp isn't as bad as the best speakers in this respect !
I am fully aware that the HRTF is also used to perceive direction (some two-channel "surroud" systems make use of this), I was just simplyfying.
Regards
Charles
Re: Re: Re: warming up!
The lifetime is not the expected time before failure. Different
manufacturers have slightly different definitions, but it usually
means that either the capacitance is no longer within specified
limits or the leakage current is above the stated max value.
Thus, you usually won't get a failure, but performance will
deteriorate over time. Electrolytics age also when not in use,
this is called shelf life, but they age more rapidly when in use.
The aging process is highly dependent on temperature, so it
is wise to design with margins, staying well below max ripple
current, for instance, to avoid high temperatures.
The lifetime varies quite a lot between brands and models.
A few examples:
Sanyo UAX low impedance: 4000h @ 85 deg. C, 1000h @ 105 deg. C
Sanyo OS-CON SA/SC: 20000h @ 85 deg. C, 2000h @ 105 deg. C
Evox Rifa PEG 124: 27500h @ 105 deg. C and max ripple current.
Suppse you tested brand new samples of these and found the
Sanyo UAX to sound best. Would you choose that one for
your amp? I wouldn't, unless the others sound terrible.
planet10 said:
The lifetime is not the expected time before failure. Different
manufacturers have slightly different definitions, but it usually
means that either the capacitance is no longer within specified
limits or the leakage current is above the stated max value.
Thus, you usually won't get a failure, but performance will
deteriorate over time. Electrolytics age also when not in use,
this is called shelf life, but they age more rapidly when in use.
The aging process is highly dependent on temperature, so it
is wise to design with margins, staying well below max ripple
current, for instance, to avoid high temperatures.
The lifetime varies quite a lot between brands and models.
A few examples:
Sanyo UAX low impedance: 4000h @ 85 deg. C, 1000h @ 105 deg. C
Sanyo OS-CON SA/SC: 20000h @ 85 deg. C, 2000h @ 105 deg. C
Evox Rifa PEG 124: 27500h @ 105 deg. C and max ripple current.
Suppse you tested brand new samples of these and found the
Sanyo UAX to sound best. Would you choose that one for
your amp? I wouldn't, unless the others sound terrible.
Here's a paradox I actually wonder about every time my family gets together.
One of my cousins has perfect pitch. She is such a musical genius that she can tell you what notes make up a chord - I lost count after 8 notes on the piano. Even with dissonance. She can tell octaves and even if one of the notes is out of tune and how much. BUT, she couldn't care less about the quality of the playback. Two questions arise:
1) How does her hearing work, versus mine or anyone else without perfect pitch?
2) Assuming she cares about the music, why can't she tell the difference between a cheap boombox and a high resolution system?
ensen.
One of my cousins has perfect pitch. She is such a musical genius that she can tell you what notes make up a chord - I lost count after 8 notes on the piano. Even with dissonance. She can tell octaves and even if one of the notes is out of tune and how much. BUT, she couldn't care less about the quality of the playback. Two questions arise:
1) How does her hearing work, versus mine or anyone else without perfect pitch?
2) Assuming she cares about the music, why can't she tell the difference between a cheap boombox and a high resolution system?
ensen.
When the amp is warm or hot the worst part is electrolytic caps!
We did use at work ERO Roederstien EKM as an all-round cap with low a price. The temperature where it was, was 50-60 deg C. The lifetime was about 3 years in continuous use. = 24kh. Suddenly the lifetime was 11 months < 8000 h. Warranty 12 months!
The lifetime at 85 deg was 2000 hours or was it 3000? It's very hard to estimate the life if you only have the datasheets. The only thing you are sure of is that a small decrease of the temperature mean many hours increased lifetime.
The we changed to Rubycon and the problems dissappeared. Nowadays we use Lelon without problems.
With this I will say that it's hard to talk about lifetime unless you have statistics. If you want to be really sure use RIFA PEH169 (made in Sweden!) or similar heavy duty parts but sometimes the product can't afford it or the part is too big.
My advice here is:
If the amp gets really hot don't have it switched on all the time UNLESS you listen to music more than 12 hours a day. If you use it a couple a times a week, switch it on when you need it. The electirical bill will also get lower.
Solder joints get stressed but seriously how often do you have to resolder? Never if the amp is good built.
BTW: Lifetime is for me when the customer complains that the product doesn't work = no or reduced capacitance = the cap is dry
We did use at work ERO Roederstien EKM as an all-round cap with low a price. The temperature where it was, was 50-60 deg C. The lifetime was about 3 years in continuous use. = 24kh. Suddenly the lifetime was 11 months < 8000 h. Warranty 12 months!
The lifetime at 85 deg was 2000 hours or was it 3000? It's very hard to estimate the life if you only have the datasheets. The only thing you are sure of is that a small decrease of the temperature mean many hours increased lifetime.The we changed to Rubycon and the problems dissappeared. Nowadays we use Lelon without problems.
With this I will say that it's hard to talk about lifetime unless you have statistics. If you want to be really sure use RIFA PEH169 (made in Sweden!) or similar heavy duty parts but sometimes the product can't afford it or the part is too big.
My advice here is:
If the amp gets really hot don't have it switched on all the time UNLESS you listen to music more than 12 hours a day. If you use it a couple a times a week, switch it on when you need it. The electirical bill will also get lower.
Solder joints get stressed but seriously how often do you have to resolder? Never if the amp is good built.
BTW: Lifetime is for me when the customer complains that the product doesn't work = no or reduced capacitance = the cap is dry
Here is a short explanation of what changes when an class AB amp goes from cold to warm:
Normally there is an optimum bias current point for the output transistors. Having the bias current higher or lower than this point will generate crossover distortion.
The optimal bias point is dependent on transistor type, emitter resistor values, supply voltage and output stage topology.
The output transistors are normally biased by applying a temperature regulated constant voltage that will track the temperature of the heatsink. This temperature tracking will for most standard amplifiers not work very well before the heatsink ( and driver / output transistors ) reach a certain steady state temperature, where the bias current has been adjusted by the amp factory.
So when the amp is switched on the Vbe of the driver and output transistors are higher than at normal heatsink temperature. When the Vbe is higher the bias current will be lower, and the crossover distortion will be higher.
Some think the crossover problems disappears because of large negative feedback, but this is not completely true, because in the crossover region the open loop gain will be lower, making the loop gain available for reducing distortion smaller.
This crossover distortion is easy to measure or observe by a distortion analyser and an oscilloscope.
The crossover distortion products consist of higher order harmonics of the input signal, and are quite annoying to the human ear.
So this makes the class AB amp sound "more" distorted than after 1/2 or 1 hour after power on.
The necessary warm-up time is different for different designs, being typically longer for amplifiers with large heatsinks.
Of course it is possible to make thermal tracking systems that minimize this problem, but "most" amplifiers using the standard amplified diode temperature compensating scheme will have some problems with too low output transistor bias current for some time before a stable operating temperature on the heatsink and driver / output transistors are reached.
best regards Noize
Normally there is an optimum bias current point for the output transistors. Having the bias current higher or lower than this point will generate crossover distortion.
The optimal bias point is dependent on transistor type, emitter resistor values, supply voltage and output stage topology.
The output transistors are normally biased by applying a temperature regulated constant voltage that will track the temperature of the heatsink. This temperature tracking will for most standard amplifiers not work very well before the heatsink ( and driver / output transistors ) reach a certain steady state temperature, where the bias current has been adjusted by the amp factory.
So when the amp is switched on the Vbe of the driver and output transistors are higher than at normal heatsink temperature. When the Vbe is higher the bias current will be lower, and the crossover distortion will be higher.
Some think the crossover problems disappears because of large negative feedback, but this is not completely true, because in the crossover region the open loop gain will be lower, making the loop gain available for reducing distortion smaller.
This crossover distortion is easy to measure or observe by a distortion analyser and an oscilloscope.
The crossover distortion products consist of higher order harmonics of the input signal, and are quite annoying to the human ear.
So this makes the class AB amp sound "more" distorted than after 1/2 or 1 hour after power on.
The necessary warm-up time is different for different designs, being typically longer for amplifiers with large heatsinks.
Of course it is possible to make thermal tracking systems that minimize this problem, but "most" amplifiers using the standard amplified diode temperature compensating scheme will have some problems with too low output transistor bias current for some time before a stable operating temperature on the heatsink and driver / output transistors are reached.
best regards Noize
Noize said:
But when cold, the Vbe multiplier will also generate a higher Vbias, which will generate higher Iq, everything else being equal.
The end result? we don't know for sure if Iq will be higher or lower at cold.
Plus, your Iq will likely move up and down depending on the load. And if Iq is the whole argument for "warm sounds better", you would have seen temperature control devices in class B amps.
But we don't see them. What does that mean?
Noize said:
we discussed this a while back. and Sloan has a total different view from yours.
Hi Charles
Now about timing. (The proof of our brain measuring time will come later!)
Did you ever remove the muting transistors from the output of a CD-player? And if so what about the difference in sound quality?
Now think! What causes this odd effect? Those transistors, when the music is playing, are in the off-state. There's no base current and so no collector current (or drain current) as well. But they "do" something, detriorating sound quality.
John
phase_accurate said:
Now about timing. (The proof of our brain measuring time will come later!)
Did you ever remove the muting transistors from the output of a CD-player? And if so what about the difference in sound quality?
Now think! What causes this odd effect? Those transistors, when the music is playing, are in the off-state. There's no base current and so no collector current (or drain current) as well. But they "do" something, detriorating sound quality.
John
Hi John
I know about the muting transistors but never tried it out by myself due to my lazyness. My CD player is already 15 years old (and therefore not anything even close to a reference) and has never failed which might be due to the fact that it is one of the only gadgets I have never opened or tried to modify.
OTOH I am still waiting for it to fail so that I have an excuse for buying one of those multi-format players.
But back to topic: I don't think that these transistors deteriorate the sound through any thermal effect or phase-shift or whatever. They are simply representing two antiparallel devices, with nonlinear behaviour, that are loading the output slightly, even when switched off.
Regards
Charles
I know about the muting transistors but never tried it out by myself due to my lazyness. My CD player is already 15 years old (and therefore not anything even close to a reference) and has never failed which might be due to the fact that it is one of the only gadgets I have never opened or tried to modify.
OTOH I am still waiting for it to fail so that I have an excuse for buying one of those multi-format players.
But back to topic: I don't think that these transistors deteriorate the sound through any thermal effect or phase-shift or whatever. They are simply representing two antiparallel devices, with nonlinear behaviour, that are loading the output slightly, even when switched off.
Regards
Charles
phase_accurate said:
Good Morning Charles
I assume you are an electronic engineer. So if you are you should know what happens when a semiconductor, say a diode, is connected in the opposite direction. If in that situation a voltage is applied the capacitance varies (varicap effect). The same is happening with mute transistors. Then calculating the cross over frequency you'll see that this phenomena acts between several hundreds of kHz and 1 MHz. Most designers assume this is not noticeable for a human listening to music. What really happens is that the stereo image is better defined and details become more noticeable, even with very old CD-players.
Nowadays there are DVD-players and surround amplifiers suffering from the same artefact. The processors recognize the signal, being it Dolby Digital, DTS, SA-CD or some other signal and then switch on the configuration which decodes that signal. This switching is done by integrated (mosfet) switches. Mosfets have larger internal capicitances then BJT's. So ..........
If you love your music you should hold on to the good old fashioned CD-player (without muting).
My experience:
Yes - amps need warming up!
Probable explanation - thermal equilibrium.
Well after repairing/tuning some amps I realised why - normal amps usually have thermo stabilisation ciurciutry (I realised that when I worked through schematics) in general it uses a small transistor which is mounted on main heatsink along with power units(or glued using thermo glue) - the problem is that power transistors heat up quicker than thermo stabilisation circiutry can sens it, when heatsink heats up evenly bias is set on its working point - presto! Sound quality is at it MAX! Generally about 15-30 min, but that varies from amp to amp.
P.S. In my native language these notations are different so my explanation may be quirky, but I hope you get the point.
As for 24/7 running - not worth it - turn it on in advance if it matters that much.
Yes - amps need warming up!
Probable explanation - thermal equilibrium.
Well after repairing/tuning some amps I realised why - normal amps usually have thermo stabilisation ciurciutry (I realised that when I worked through schematics) in general it uses a small transistor which is mounted on main heatsink along with power units(or glued using thermo glue) - the problem is that power transistors heat up quicker than thermo stabilisation circiutry can sens it, when heatsink heats up evenly bias is set on its working point - presto! Sound quality is at it MAX! Generally about 15-30 min, but that varies from amp to amp.
P.S. In my native language these notations are different so my explanation may be quirky, but I hope you get the point.
As for 24/7 running - not worth it - turn it on in advance if it matters that much.
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