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Old 21st October 2012, 06:44 PM   #21
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Default I have built and MKII prototype is working

Here you can see:

Dx Super A - MKII - YouTube

regards,

Carlos
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Last DIY amplifier posted is Dx Super A, the future unit to be released is exclusive to Brazil, to be sold here, for Brazilians only: https://www.youtube.com/watch?v=O_qpaKd2rAw
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Old 22nd October 2012, 03:52 AM   #22
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Default What i did with this circuit

The former one, previous one, have not reduced the bias in the amount i wanted....so..... it was forcing more current than needed to the output transistors at power higher than the threshold previously decided to jump from class A to class AB.

Because of that i have made the standard and traditional VBE multiplier...then i have adjusted the current to 250 miliamperes in stand by mode.

A zener diode connected to the ouput line make the rectification of output audio and also presets, because zener effect (only conducts with voltages higher than the component zener voltage) will send current to control de VBE multiplier transistor base.... reducing the DC bias current, gradually, as the current crossing this zener diode increases...... having current increase we gonna have VBE multiplier settings decrease, till it reaches the minimum that is more or less 40 miliamperes (this is adjustable and i am studying and listening to decide the best settings)

It is working fine...but i have to study the graphic of DC current in the output transistors due to this circuit in operation compared to the standard and traditional Class AB operation.

Circuit is simple...very simple.... the zener is "fooling" the VBE multiplier base.

I am controling using half wave...because i assume these two halves of the waveform are the same in amplitude...so... referenced by the positive or negative cicle will result the same.

regards,

Carlos
Attached Images
File Type: jpg Charlie foto recente.jpg (302.0 KB, 1110 views)
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Last DIY amplifier posted is Dx Super A, the future unit to be released is exclusive to Brazil, to be sold here, for Brazilians only: https://www.youtube.com/watch?v=O_qpaKd2rAw

Last edited by destroyer X; 22nd October 2012 at 03:56 AM.
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Old 22nd October 2012, 09:27 AM   #23
AndrewT is offline AndrewT  Scotland
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Thanks for trying to explain.
I can't follow the logic and don't know what your are trying to achieve.
As a result I can't help with any advice.
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Old 22nd October 2012, 06:26 PM   #24
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Default I want to have an amplifier that operates in class A (30% efficiency) ...

till it reaches 5 watts RMS of output power... reason why i have preset my current to 250 mA when operating 42 plus 42 volts...so... consumption is 21 watts in stand by mode..... 30 percent of that is 7 watts.... i do accept 5W as good.

Also i want something to switch (Super A circuit, or any circuit able to do that) this stable current in order to reduce it, gradually, till i reach the 20mA per rail bias.... say.... when the amplifier will be full power, its consumption will be 1.7A each rail (class AB), power will be almost 100 watts rms....but all that current will be the result of audio driving the circuit.... DC bias will be there just to be there, almost zero..... so, consumption will be the circuit demand to produce the full power without any waste of current.... going to 55 to 65 percent efficiency.

I have already made...it was assembled, it is being tested...several videos published showing the sound....this circuit shown, the Super A - MKII is the one i am listening..and it is going to 5 watts in class A.

What i call class A?

The same definition Rodd Elliot gives to us in his page:

Class-A Amplifiers explained

here is the schematic...i do think i have already found the solution, but suggestions and help are always welcome.

The way i have used to measure will be explained in video to be made, also new chart of current will be show in the video.

This circuit is approval pending.... i am still listening and testing..it is not ready to go.

regards,

Carlos
Attached Files
File Type: pdf Dx Super A - MKII.pdf (61.0 KB, 371 views)
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Last DIY amplifier posted is Dx Super A, the future unit to be released is exclusive to Brazil, to be sold here, for Brazilians only: https://www.youtube.com/watch?v=O_qpaKd2rAw

Last edited by destroyer X; 22nd October 2012 at 06:30 PM.
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Old 22nd October 2012, 07:15 PM   #25
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Default In the simulator it is perfect...or almost perfect

It is flat from 5 hertz to much more than 100 kilohertz... sinusoidal waveform starts to become triangle around 130 Kilohertz ... when you inject sinusoidal and observe it full power on the scope screen.

AC analisis and fourier analisis perfect too.

I am listening searching for noises and strange modulations due to DC bias variations... say.. floating around the zero.... reference line floating compared to the zero volts.... also intermodulation and transients.

One point to be observed and tested using thermal heaters is the thermal compensation and the absence of dangerous levels of thermal drift...also i want to know if this Super A current will have to be ajusted with the unit hot or with the unit cool..i have some doubts about and i want to check.... in my imagination, as it will work hot, the adjustment should be made while hot.

For a while all that stuff is fun and enjoyment to me.....to be sure i will be making and offering the ultimate audio amplifier.

I do think i have made a lot of progress this half century or search and research...from the units that exploded in my face, i can now a days feel pride that i could create and offer for free, nice amplifiers to the community, sharing not only good sonics but also passion.

regards,

Carlos
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Last DIY amplifier posted is Dx Super A, the future unit to be released is exclusive to Brazil, to be sold here, for Brazilians only: https://www.youtube.com/watch?v=O_qpaKd2rAw

Last edited by destroyer X; 22nd October 2012 at 07:21 PM.
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Old 23rd October 2012, 08:01 AM   #26
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Default I am glad to inform you, dear friends, i have finished the Dx Super A - MKII tuning

into the simulator...now i will tune it real life (very different).

At the simulator it is glorious, unbeatable, awesome, super, wonderful and marvellous... and what this represents?....nothing!...numbers are just numbers...BUT... feed the believer's soul with strong faith.

Well...all i want was to reduce third harmonic compared to the second harmonic....another targed was to reduce it when compared to the Dx Blame ST, that is (WAS) the best ever made, wide world, audio amplifier.

I will post a chart and a graphic from the Dx Blame ST

regards,

Carlos
Attached Images
File Type: jpg Dx Blame ST - AC analisis.jpg (118.5 KB, 989 views)
File Type: jpg Blame ST fourier.jpg (343.2 KB, 954 views)
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Old 23rd October 2012, 08:04 AM   #27
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Default What i had in the first moment, before i have tweaked

I am posting images from the Dx Super A - MKII before simulator tweak.

Observe the small difference from second to third harmonic...this pollutes the sound a lot....not a good result.

regards,

Carlos
Attached Images
File Type: jpg Dx Super A - AC analisis.jpg (127.9 KB, 864 views)
File Type: jpg Dx Super A - MKII - first Fourier analisis made.jpg (340.7 KB, 834 views)
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Old 23rd October 2012, 08:06 AM   #28
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Default Now see after a couple of hours tweaking

A much better result..observe THD and observe, mainly, second to third harmonic...we love the second and we hate the third (humans audition perception)

You see...not a good progress.

regards,

Carlos
Attached Images
File Type: jpg Dx Super A - MKII - Second Fourier analisis made.jpg (313.2 KB, 140 views)
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Old 23rd October 2012, 08:09 AM   #29
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Default But here you have final result.

Left side without with Super A circuit OFF....right side you have Super A circuit ON, because i have included a switch

Carlos
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Old 23rd October 2012, 08:13 AM   #30
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Default Here you see two images...one with Super A circuit ON and the next one with

circuit Super A OFF.

You see it is not messing the results..we can use it on.... to put a switch into the pcboard ( i will arrange the together Juan Vargas) or to put wire jumper if you decide to use it ON or OFF permanently.

You see...the different when it is on and off does not appear in the THD meter.... because very small.

regards,

Carlos
Attached Images
File Type: jpg Dx Super A - MKII - ON-OFF switch (2).jpg (247.4 KB, 141 views)
File Type: jpg Dx Super A - MKII - ON-OFF switch.jpg (310.2 KB, 124 views)
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Last DIY amplifier posted is Dx Super A, the future unit to be released is exclusive to Brazil, to be sold here, for Brazilians only: https://www.youtube.com/watch?v=O_qpaKd2rAw

Last edited by destroyer X; 23rd October 2012 at 08:15 AM.
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