Since you brought up the ML-2 which is a 25W (iirc?) class A amp, perhaps it would help you to read Nelson Pass' short paper called 'Leaving Class A.'
Dear Mr. Pearson,
i understand your brother was a very special and kind person.
I have somewhat lost my faith in the existence of a good God, because the life of many very good people has been too short and that of very bad people too long.
gino
Good morning !
thanks a lot indeed for the valuable recommendation.
To be honest i tried to read a very basic book on electronics ... but it is difficult.
I have been always very bad at math
I see. But i agree with those who say that a power amp that doubles the power passing from 8 to 4 ohm has a very good power supply.
Instead some amps have almost the same power on both loads.
Do you recommend a good speakers selection ? but what if you really like the sound of a very difficult speaker like the Scintillas ? would you give up to the idea ?
Let's make an analogy in that respect. You don't make a sports car for everyday use to weigh 3 tons with an engine of 2000 hp when you can make a Porsche.
I agree. But again to have an amp that can drive properly more speakers opens the number of possible speakers options.
I like the idea to have an amp as a solid corner stone of my system a lot.
Thanks again
Hi and thanks a lot for the very valuable advice.
Where i can find that paper ?
However i have a very old doubt about class A.
First, some class AB amps sound better than other class A amps. I mean class A is not always a guarantee of good sound.
And then i post a question already in this forum long time ago.
Let's take the mighty ML-2.
I do not know how high it is biased. Let's say that is biased to give the equivalent of 25W (i.e. 100% class A).
I asked ... if i bias the same amp lower, like let's say 5W ... would i be able to feel any "practical" difference in sound ?
i do not think so.
If i had the ML-2 i will try to bias it lower for sure and listen to it.
My guess is that the very powerful and nice sound is dictated more by the exceptional power supply and it is available with lower bias levels as well.
I see the amp like a car engine ... the idle must be only enough to keep the engine running.
There is no use to keep the engine rotating at 3000 rpm when the car is still.
Maybe i am wrong.
However i have not been able to get any answer from anyone who has actually done this kind of test. No one.
They always follow the designer advice on bias setting.
Thanks again, gino
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like a car engine the amplifier bias can have a "sweet spot".
The car's engine stalls if set too low, the transistor moves to a less than optimum operating condition when the current is reduced.
Have a look at hFE vs Ic and fT vs Ic. They are rarely flat, indicating that they work the same at any current (Ic).
If the amplifier is always in the range of ClassA output current then that amplifier can never have "crossover distortion".
If one biases to a lower level so that some current demands fall outside the ClassA limit then that amplifier will have some crossover distortion. This is added distortion that is avoidable.
The car's engine stalls if set too low, the transistor moves to a less than optimum operating condition when the current is reduced.
Have a look at hFE vs Ic and fT vs Ic. They are rarely flat, indicating that they work the same at any current (Ic).
If the amplifier is always in the range of ClassA output current then that amplifier can never have "crossover distortion".
If one biases to a lower level so that some current demands fall outside the ClassA limit then that amplifier will have some crossover distortion. This is added distortion that is avoidable.
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Hi and thanks a lot for the extremely interesting explanation
I have really to study a little more to understand better. I lack the basics.
I really need to understand this concept of optimum operating condition for a transistor .
I have to start with the transistor and its behaviour before moving to more complex things. I will try soon i promise.
The bias is a very important issue.
A silly question ... a what level crossover distortion starts to be evident during the listening ?
And again i do not understand why no one has ever tried to bias a very "hot" amp lower. I do not say to zero ... but something like 1/10th of the max power.
Or 1/5th of that power.
I see this ML-2 ... i guess it is 100% class A ... it is scaring what kind of heatsink "only" 25W require ... unbelievable.
I do not have any idea how hot those huge and wide fins get anyway. Maybe not that much ? maybe they have been oversized ?
However it is also a fact that amps operating in class AB do have a very nice sound. Maybe by virtue of a better design ?
My friend has two monos ... they stay completely cold on fins at idle (i guess a very very low bias current). And still the sound is very good.
I have to study first.
Thanks a alot again. Gino
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This is almost always the case with DIYers, they would overdo
any aspect of performance just for the sake of it, so they can say
their creation rules.
You see, manufacturers have come to a conclusion that users
don't need nowhere near enough power they think they do, so
they made their business easier and more profitable.
If your loving wife weighs substantially more than you, then you
better make sure she doesn't crush you or do something about
your robustness
.I agree. But again to have an amp that can drive properly more speakers
opens the number of possible speakers options.
an amp as a solid corner stone of my system a lot.
Thanks again
Any decent amp can drive any speaker, the question is at what power output.
After all, isn't your health so much more valuable than audiophile pride?
How much SPL do you really need, ought to be answered first. Have fun!
id suggest either measuring or modeling the bass woofer as to what current it demands and then take it from there. if you have access to MS excel there is a free tool you can download and look at a chart of Current Vs frequency for any woofer alignment in a box. many people like you assume unrealistic currents are needed. this is not true esp on woofers with series inductors >L slows dynamic current right!here is where i do not agree.
The circuit for me is like a water tap. If you do not have pressure upstream you can fully open the tap but the outcome will be weak.
The "pressure" is the current coming from the power supply and the transformer, very little talked about, can be the first and decisive bottle-neck for current.
I strongly need an high current amp. Not many watts instead.
20-30 can be enough ... something like the First Watt or similar.
And i guess it will be DIY .. in the end.
Thanks a lot again.
Kind regards, gino
old school amps were designed by classical trained engineers for sinewaves into resistors> in practice with real music the heatsinks and transformer stays cool >this is only a sign of waste not good sound. BTW the amp weak link is the # of output devices for high demand currents into low ohm speakers with more modern transistors are more capable by almost 2x.
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Hi !
i have a question related to a story.
A friend of mine owns two small but nice mono amps, Albarry m408.
Then he tried the integrated from the same brand that is exactly the same design in one box but with just one transformer and a pair of ps caps, the same parts that can be found in each monos.
Driving a pair of full range speakers there was absolutely no story.
The two monos sounded so much more convincing that he was even surprised given the same design.
Of course the ps power was doubled.
So my question is ... if i take a small but nice integrated of which i like the sound a lot and i double both transformer VA and ps caps uF can i expect a similarly remarkable improvement in sound ?
Moreover in the case above, a transformer double the size and 4 caps would have given to the integrated the same sound of the two monos ?
thanks and regards, gino
Please be aware of the fact that since music (even clipped and overcompressed) has a relatively high crest factor and that amps are rated using sine waves with a relatively low crest factor, most audio amps are violently overbuilt. Therefore the probable cause of your perceptions may be listener bias.
This is almost always the case with DIYers, they would overdo any aspect of performance just for the sake of it, so they can say their creation rules.
You see, manufacturers have come to a conclusion that users don't need nowhere near enough power they think they do, so they made their business easier and more profitable
Hi i am sure you are perfectly right. But i think that speaking of commercial amps the audiophiles who are not able at DIY they look more at the quality 2nd hand market than to more recent offerings.
If your loving wife weighs substantially more than you, then you better make sure she doesn't crush you or do something about your robustness
no wives
but neighbours yes ! they are so silent that i am worried to make any noise. Sometimes i think that they are dead. Zero noise.
Usually i have efficient speakers and the room is small.
I think that 10 robust Watt should be more than enough.
And i like a lot the 2 monos solution in order to place the amps as close as possible to speakers.
Something like the poor guy ML-2 ? but biased lower
Thanks again, gino
One way to further one's understanding of what's going on inside power amps is to measure one while it is doing its usual thing.
In surveys of consumer power amps, one finds evidence that a lot of people are using vastly overpowered amps. It is typical of these amps for their intenal voltages to be reasonably stable.
The exact question that is being asked may be a bit of a trick question because the amp at hand is actually pretty atypical compared to say, a typical AVR.
In particular the AVR power output stage will probably have a ton more power supply rejection. It will also typically have a lot more power output.
Hi ! this is too difficult indeed.
My DIY ambitions are confined to electronics mods/upgrades.
then i do not understand why doubling the PS resulted in better sound in my friend's case. He is quite sure of this.
i think i have expressed myself badly. The amp is cold at idle and remains cold with no signal applied. With the music warms up of course.
Sorry you mean the number of output devices ?
I need few W no more than 10 i think.
I think that one pair per channel should be enough ?
Thanks again. gino
Hi and thanks and this is difficult.
My feeling is that is not the circuit that is stressed but the power supply.
Again, upgrading the ps with more VA and uF could bring some improvements in audible and also measurable performances. Keeping all other things unchenged.
This is my feeling at least.
Regards, gino
Amplifiers that doubles the power passing from 8 to 4 ohm has a very good advertising copy writer.
If you are made privy to bench tests of amps that meet this spec, you will that almost inevitably find their 8 ohm ratings are understated.
There may be exceptions, but without trick circuits such as negative resistance power supplies, they violate the law of conservation of energy.
Well, that's the other extreme, and one almost never actually finds it in the real world, either.
I judge amps using tough standards - the rules of electrical engineering and carefully controlled double blind listening tests.
The most under built component of a modern power amp or receiver is indeed typically the power supply, but for the reasons already given, it is still very infrequently the cause of audible difficulties.
Now listener bias, that is about as easy to find as it is to look for it. ;-)
strange to limit yourself on your quest, can you modify a spreadsheet ?
the speaker determines what is needed by an amplifier yes?
model some several very demanding woofers in their boxes and you will see a trend, very useful!
I cant answer this. perhaps more testing/listening by limiting the variables. was everything exactly the same except the PS?
you realize PS rail decoupling is what separates the good from great designs no?
I'm sure you are coming to a wrong conclusion from your statements above
ofcourse is this a revealing something ?
the better amps will be warm at idle not cold, maybe you prefer more Xover distorsion IDK.
depends if you compare a robust audio amp , one that almost doubles the power from 8 to 4 you will notice the transformer is usually the weak link AND the output stage must provide many more devices / to a bigger heat sink. but many OEMs don't like to provide free power so this has to be examined more closely on a case by case basis. but again you will never stress the transformer/s & heat sinks on these, using "normal" speakers listening to music. again examine your speakers to determine YOUR needs!
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There are increasingly common modern output devices that have the same or more capacity than the multiple devices we had back in the days when multiple devices were required and thus common. We're talking 3-4x or more.
This was achieved by improvements in device construction and processing
Multiple devices were usually required to handle speakers that were very reactive. These demands were usually short term, so heat sink upgrades were not required as things developed.
yes I spoke to some improvements in modern devices but the heat sink requirements don't change all that much for straight bench tests. BIG ones they are seen for non class H into low ohms. RE ones the OP likes but probably cant use properly.
sure many amplifier designers over estimate speaker demands as well as their users.
but there's nothing wrong with conservative load line and SOA protection. devices are cheap compared to the iron copper and aluminum. there's always the early flat panel speakers to roll out to test worst case.
sure many amplifier designers over estimate speaker demands as well as their users.
but there's nothing wrong with conservative load line and SOA protection. devices are cheap compared to the iron copper and aluminum. there's always the early flat panel speakers to roll out to test worst case.
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So my feelings are right ? i am sure that not only the rating but also the quality of mains transformers and ps caps in many commercial amps, and even not cheap ones, is very poor
Because quality comes expensive.
Maybe the amps you normally test are all very high quality.
I remember one magazine performing the power cube test.
This is the different behavior of 3 amps at the test
http://www.bostonaudiosociety.org/images/meetings/audiograph_result1.gif
does this reflect on sound ? i guess so especially in presence of difficult speakers. I would like better the amp on the left.
your good, better, best, pictures are for 'consumer reports' crowd
high power doesn't always = high quality nor good sound
it can be useful to show where to look if YOUR speakers are low ohms AND operated at high SPLs.
one thing for sure high power into low ohms comes at a cost$ but it might or might not sound great for Hi-Fi.
high power doesn't always = high quality nor good sound
it can be useful to show where to look if YOUR speakers are low ohms AND operated at high SPLs.
one thing for sure high power into low ohms comes at a cost$ but it might or might not sound great for Hi-Fi.
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