i'm very interested in this, since i have never been able to work out where this magic extra 2 times current comes from when you add one amp driving positive phase to another driving negative phase, how do you have 4 times the drive with only 2 x the power?
i realise the impedance is halved, but isnt there still only 2 x the power/current to pull from? or is it just as simple as that, the impedance is halved so the same power over half the resistance = double the drive, so you have x 2 by doubling the amp and another x 2 by halving the impedance?
but then you have some amps that will not put double the power into half the load as they are optimized for higher loads. arrgghh
i realise the impedance is halved, but isnt there still only 2 x the power/current to pull from? or is it just as simple as that, the impedance is halved so the same power over half the resistance = double the drive, so you have x 2 by doubling the amp and another x 2 by halving the impedance?
but then you have some amps that will not put double the power into half the load as they are optimized for higher loads. arrgghh
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a 25watt F5 puts out 12watt classA into 4ohm, right
how does that affect a balanced/bridged version, when 8ohm load is presented as 4ohm
if you have say a 40watt balanced amp, the reality is 20watt classA, no ?
ok, it is more than 12watt
and theres more 'peak power'
btw, please remember that there are very few 8ohm multiway speakers, but more like 5-6 ohm, at best
if you want 100% pure classA, it seems to me that both low impedance speakers and balanced design is a bit of a 'pain'
how does that affect a balanced/bridged version, when 8ohm load is presented as 4ohm
if you have say a 40watt balanced amp, the reality is 20watt classA, no ?
ok, it is more than 12watt
and theres more 'peak power'
btw, please remember that there are very few 8ohm multiway speakers, but more like 5-6 ohm, at best
if you want 100% pure classA, it seems to me that both low impedance speakers and balanced design is a bit of a 'pain'
Sorry having confused someones.
After my last post, i realised that my post 987 and some others were wrong.
Two balanced stock F5 balanced biased at 1.3 each produce 25w classA and not 12.5W.
I am stupid.
Even looking at the drawing with virtual ground, it can be seen that each amp produces simultaneously 12.5W classA into half the load, which is 25w total into the whole load.
After my last post, i realised that my post 987 and some others were wrong.
Two balanced stock F5 balanced biased at 1.3 each produce 25w classA and not 12.5W.
I am stupid.
Even looking at the drawing with virtual ground, it can be seen that each amp produces simultaneously 12.5W classA into half the load, which is 25w total into the whole load.
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> since i have never been able to work out where this magic extra 2 times current comes from when you add one amp driving positive phase to another driving negative phase,
You don't if you stick to 24V 1.3A per FET as in F5-SE.
But if you change to 2A 16V, you increase the bias current by a factor of 1.5, and decrease voltage by the same factor to keep dissipation of the FET constant. i.e. it is not the balanced circuit that gives you more current (it only gives you more voltage across the load), but the change in bias that you do on purpose.
> how do you have 4 times the drive with only 2 x the power?
If you design the amplifier to be current limiting (i.e. you have some voltage headroom to spare), then 1.5x increase in current gives you approx. 2x increase in power (I2R). The world has not fallen apart.
Patrick
You don't if you stick to 24V 1.3A per FET as in F5-SE.
But if you change to 2A 16V, you increase the bias current by a factor of 1.5, and decrease voltage by the same factor to keep dissipation of the FET constant. i.e. it is not the balanced circuit that gives you more current (it only gives you more voltage across the load), but the change in bias that you do on purpose.
> how do you have 4 times the drive with only 2 x the power?
If you design the amplifier to be current limiting (i.e. you have some voltage headroom to spare), then 1.5x increase in current gives you approx. 2x increase in power (I2R). The world has not fallen apart.
Patrick
I think all this confusion in amongst some very correct science is brought about by two quite different "wives tales".
First. It is wrong to say a bridged pair or balanced amplifier delivers 4times the power.
Second. It is wrong to say a ClassA amplifier draws constant current.
These two errors in understanding are so ingrained into our thinking that they are subtly altering our ability to reach experimentally based or thought based conclusions.
You must go back to the correct versions of the two statements.
A bridged pair or balanced amplifier delivers double the power into double the impedance.
A ClassA amplifier modulates the current demand in the supply rail/s to match the modulated current fed to the load.
Many parts of the recent discussion are accurate. But, in between, there are many statement that are simply wrong.
To allow future readers to understand the concepts being explained here:- Do we need to remove all the erroneous "facts"?
First. It is wrong to say a bridged pair or balanced amplifier delivers 4times the power.
Second. It is wrong to say a ClassA amplifier draws constant current.
These two errors in understanding are so ingrained into our thinking that they are subtly altering our ability to reach experimentally based or thought based conclusions.
You must go back to the correct versions of the two statements.
A bridged pair or balanced amplifier delivers double the power into double the impedance.
A ClassA amplifier modulates the current demand in the supply rail/s to match the modulated current fed to the load.
Many parts of the recent discussion are accurate. But, in between, there are many statement that are simply wrong.
To allow future readers to understand the concepts being explained here:- Do we need to remove all the erroneous "facts"?
now this will be interesting, thankyou for bringing up this, its exactly what i want cleared up, because its been bugging the hell out of me as it makes no sense. it is repeated ad nauseam around this and other audio forums so much that it is spoken as fact, so i have been bending otyher rules this way and that to try and make it fit
That is forum life. Every writen thing is not to trust.
But it's how it works.
I fear moderators would get too heavy a task to sort it.
May be some wiki should be writen instead, abrastracting the main ideas.
A whole job that requires knowledge, writing and pedagogical talent ... and time.
It should be illustrated also.
Such as Nelson's articles?
But it's how it works.
I fear moderators would get too heavy a task to sort it.
May be some wiki should be writen instead, abrastracting the main ideas.
A whole job that requires knowledge, writing and pedagogical talent ... and time.
It should be illustrated also.
Such as Nelson's articles?
That is forum life. Every writen thing is not to trust.
But it's how it works.
I fear moderators would get too heavy a task to sort it.
May be some wiki should be writen instead, abrastracting the main ideas.
A whole job that requires knowledge, writing and pedagogical talent ... and time.
It should be illustrated also.
Such as Nelson's articles?
touche
yes of course, his articles as well as other technical texts and plain vanilla logic speak the truth, but we also deal with many things that are either ahead of or ignored by such articles and branches of science (not nelsons of course). lately because ive had to actively start to think about such things for this build, its been annoying me because it rears its ugly head in many threads i have researched, so i'm glad its been cleared up at least for my sake and those who read this thread carefully as even in here it has been a little muddied by the influence of this fallacy.no reason to remove good posts
conclusion is good, and so was the debate, and obviously needed
anyway
those who dont care to read and learn, can go directly to the conclusion
seem ok to me
and we have the original F5
with all the needed details but same thing, about reading
read F5 maual, read it all, and study all details
if in doubt, go back and read again, and again
doesnt matter if one understands it or not
you should know every detail in there
and dont forget the supply schematic, right at the end
do I sound boring, maybe
but I made the mistake myself
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