Honest, no clue, as I only measured the output voltage trough the 8ohm resistor. (as well as the idle current) By that time I was already "fed-up" with the design, as I had to go trough all kind of unmentioned issues to make it work.
Eric
If you don't know what the maximum ClassA output current is, or could be, then you have no evidence for your claim that the maximum ClassA output power is 70W !
If one knew that the ClassA limit was 2.4Apk then the maximum ClassA power would be 23W.
But you have to identify the current first to be able to work out what the power is.
If one knew that the ClassA limit was 2.4Apk then the maximum ClassA power would be 23W.
But you have to identify the current first to be able to work out what the power is.
How about placing a 8ohm resistor and mesuring the AC Voltage at clipping? Then apply the formula Vrms squared/ resistance? Does this qualify? I tough it was a standard way of measuring. By the way is you are interested I will send you a PDF of the 2 Articles as well as leftover pcb's with LM117 and IRF150's...
That test is the standard for finding the maximum power output.
The only part missing is the check for distortion to ensure you are clear of clipping.
THD is usually specified @ 0.1% for a full power Test.
This tells you nothing about whether it is ClassA or ClassAB or any other Class.
The only part missing is the check for distortion to ensure you are clear of clipping.
THD is usually specified @ 0.1% for a full power Test.
This tells you nothing about whether it is ClassA or ClassAB or any other Class.
The scope pic of the output does not tell you about ClassA.
You need to see the current flow through the output devices.
For ClassA all the output devices must actively control the current flow to the output over the full 360° cycle of the waveform.
You need to see the current flow through the output devices.
For ClassA all the output devices must actively control the current flow to the output over the full 360° cycle of the waveform.
To produce 70W rms, an amplifier such as this with a source follower and constant current source would need a quiescent current of roughly 4.2A, and a voltage rail over 70V so as to produce 33.4V peaks across 8 ohms. Quiescent power dissipation will be around 300W.
This amplifier has 42 volt * 2 voltage rail = 84 volt.Lm 317HVK can produce 1,5 A each one .There are 4 in this amp= 6 A max .I think 4A is save quiescent current.It only needs proper hitsink of course.
If we take 4 A as a quiescent current ,it means that is a "zero cross" point of a sine wave.The top of a sine wave current is 6 A and the bottom is 2 A on a linear part of a IRF 150 characteristics.The diffrential current making power of this amp is 4 A.According to french description in the magazine this amp make 23,57 Vrms on the 7,8 load .It makes 71 watt power.
70W class A is a very big amplifer. If you look on the forum, I posted up a link to a write up on my new class A amp (the 'Ovation sx-Amp') which is rated at 15W RMS per channel pure class A. In the write-up (page 11) is the formula for calculating the required class A current.
My suggestion is that if you need power, go class AB (they can sound astounding!) - and if you want some class A magic for the mid and upper registers, go class A - but something like 20W on resonably sensitive speakers should be more than enough. For the sx-Amp, I am using 0.4degC/W heatsinks (well, thats what RS rate them at!) per channel and after 30 minutes, they are sitting at between 65C and 70C. Thats for 15W class A. For 70W you will need something very much larger, and no doubt will have to consider forced cooling as well.
Anyway, good luck with your project! (good idea to stick the amp out in the snow BTW!)
My suggestion is that if you need power, go class AB (they can sound astounding!) - and if you want some class A magic for the mid and upper registers, go class A - but something like 20W on resonably sensitive speakers should be more than enough. For the sx-Amp, I am using 0.4degC/W heatsinks (well, thats what RS rate them at!) per channel and after 30 minutes, they are sitting at between 65C and 70C. Thats for 15W class A. For 70W you will need something very much larger, and no doubt will have to consider forced cooling as well.
Anyway, good luck with your project! (good idea to stick the amp out in the snow BTW!)
This A class amp needs one 500 W trafo for each one channel.1000 W for both.It has really big power consumption.
Consider Rod Eliot's P3a class AB DIY design - has a large fan base, and from what I've read with good reason.
60-80W Power Amplifier
Elsewhere on this forum you can find a thread started by a repair tech in Greece who refers to his p3a as his reference amp.
http://www.diyaudio.com/forums/solid-state/164756-p3a-comparsion-table-long.html
Same for a thread on diyaudioprojects.com
DIY Audio Projects Forum • Elliot Sound Products - P3A 100W Amplifier
...and save the rest for a P3A! If I had the EE savy, I'd go this route myself.
As side note: Rod has a P3B essentially A class a version of the P3a.
Cheers, Tony
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