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Old 21st October 2012, 10:13 AM   #11
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Default Here you have some adjustment instructions, also some other details

... including a more clear diagram that will be easier to understand how the subcircuits interact one each other.

regards,

Carlos
Attached Images
File Type: jpg Dx Super A circuit inside green frame.jpg (263.1 KB, 1352 views)
File Type: jpg Adjustment points and details.jpg (624.7 KB, 1287 views)
Attached Files
File Type: pdf Blame Super A - a more clean diagram.pdf (57.2 KB, 266 views)
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 21st October 2012, 10:20 AM   #12
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Default Here you have a comparison of current to the Dx Blame St with and without Super A

I will explain better near future, a video will be made.

You see it leaves the class A operation at 1.4 watts aproximatelly.

The bias is adjusted to 250 mA...then after we reach 1.4 watts aprox, the output voltage level rectified by the 1N4148 diodes triggers the circuit to reduce the current to class AB and then class B standards.

The current selection was made in order to keep heat under control...but you may need a fan if your heatsink is small or if your heatsink will be inside an enclosure....observe that 0.25A multiplied by the supply voltage result in 10.5 watts...and this to each rail.... so...we gonna have 21 watts of heat.

So, you can increase if you want...but do that under your own risk...i tried with 0.25A and the unit survived..if you push it hard do it by yourself and do not ask my help to produce a coffee heater (Class A) that may be very unconfortable inside your living room unless you live in Sweden

I have pushed this amplifier hard with 3 ohms speakers (two 6 ohms units in parallel) and a single output pair survived..so.... i believe two pairs may face 2 ohms without problems if you keep the supply voltage at 42 plus 42 volts DC or less than that.

I have used the strongest transistors i have at the output (attached datasheet).

regards,

Carlos
Attached Images
File Type: jpg Comparação Standard e Super A.jpg (391.4 KB, 1108 views)
Attached Files
File Type: pdf MJL4302A e MJL4281A.pdf (59.2 KB, 168 views)
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg

Last edited by destroyer X; 21st October 2012 at 10:28 AM.
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Old 21st October 2012, 11:17 AM   #13
AndrewT is offline AndrewT  Scotland
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C,
what is the table in post12 telling us?
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regards Andrew T.
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Old 21st October 2012, 11:49 AM   #14
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Default This circuit was applied in a Gradiente Receiver that result champion of sales

in Brasil...now a days people fight to buy one or two that from time to time appear in Brazilian E bay.

Brazilian unit goes to 10 watts in class A.... it is too much hot...but considered the best ever made amplifier.

People can increase the bias if they want...then will be alike the Model 366.

This kind of circuit was licensed by JVC to be used in our Receivers..they had something alike in Japan too.

regards,

Carlos
Attached Images
File Type: jpg Gradiente Super A.jpg (105.2 KB, 941 views)
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg

Last edited by destroyer X; 21st October 2012 at 11:52 AM.
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Old 21st October 2012, 12:08 PM   #15
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Default Doubts about how it operates i can help, but doubts about the design

values of current, points of adjustment and so on or any troubles about the circuit...or complain related what Gradiente did with their design..then go direct to JVC:

12, 3-Chome, Moriya-cho, Kanagawa-ku, Yokohama 221-8528, Japan

The one i have made was tested..it works..it is stable...sound increase in low volumes naturally and it is not sucking more current at high power than an average class AB amplifier will drain.

regards,

Carlos
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Old 21st October 2012, 12:35 PM   #16
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Default I have tried this same amplifier adjusting bias to 250 mA without the Super A circuit

Performance was different.... distorted more and heat was bigger too...it is not the same if you increase the stand by bias...dinamically it operated to reduce the extra biasing current.

regards,

Carlos
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Old 21st October 2012, 02:28 PM   #17
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Default Please boys...do not build...i found a mistake.... current tracking is not

Happening the way i want...give me a break and i will try to tune it better.

I am sorry...but inspecting in details i found it is not reducing the current in the ammount i want and need...there's some error there.

regards,

Carlos
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Old 21st October 2012, 02:37 PM   #18
AndrewT is offline AndrewT  Scotland
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Is idle current reduction what you want/need?

What does the SuperA circuit try to achieve?
I guess it is supposed to offer some improvement over what "ordinary" ClassAB has to offer.

If optimum ClassAB bias is set up, then the maximum ClassA current is fixed by that optimum ClassAB bias current. It cannot be any different.

What does SuperA do that is "improved" cf. optimum ClassAB?
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Old 21st October 2012, 04:26 PM   #19
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Default Inside the range of class A operation it improves sonics because reduces

crossover distortion setting up a higher stand by current.... to a couple of watts, while operating class A it sounds better...so, sounds better at low volumes, exactly the range of volume/power we often use when we are enjoying music....we use around 2 watts per channel..this is what i could see observing my friends when listening relaxed and out from "demonstration mode"

When we increase volume, as you know Andrew, we collect output audio voltage that is rectified...and this DC will trigger the VBE multiplier circuit in order to reduce the DC bias... from now on, audio signal will now be biasing driver and power transistors (Class B) and we do not need anymore the previous 250 mA adjusted in stand by mode.... so...the idea is to go reducing this DC bias as we increase the volume in order to offer 40 to 80 miliamperes of DC bias only.... then the increase of current will follow transistor base to collector gain of current, tracked and reference by the audio current entering these transistor base to emitter junctions...so, audio current will do it for us.

I have made another one.... i found current tracking very strange with the original one..so, i have simulated and will test this variation, i am calling MKII, and i hope it gonna work... at least it is simulating fine...let's see the real thing.

Tomorrow is a working day for me...i am a little bit old and i return from work dead tired..sometimes i go to the bed to sleep, so tired i become...i am not sure if i can do that tomorrow...but these next three days i will try different circuits.

Schematic, without values posted.... values will be adjusted in real life, and it is a waste of time to publish simulated values.

regards,

Carlos
Attached Files
File Type: pdf Dx Super A - MKII.pdf (19.9 KB, 439 views)
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg

Last edited by destroyer X; 21st October 2012 at 04:31 PM.
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Old 21st October 2012, 04:42 PM   #20
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Default This name Super A i understand because it is a kind of evolution

Related class biasing.... something Super... extraordinary.... that has a JVC patent.

When we adjust DC bias to 1A in a class A audio amplifier, then you will have this DC bias to low, mid and high volume...audio will change (modulate) this current.

In the Super A, you have high current to low power only.... after that, when we go increasing volume, this DC bias is cutted of or reduced to a low level, and then the audio itself will drive transistors.

In the first sittuation we have that high current all time long....in the second sittuation the current goes to a couple of watts and then is reduced, not beeing added to the audio current.

This reduces current and heat generated.... the amplifier goes to Class AB or even Class B operation after we go above the previously decide threshold of power we want the circuit to switch or operate the DC current in a linear way.

You know?... why to keep high DC current if audio current will already do the job .... small audio, or audio pauses, will result in reduction of current into the Super A mode, but when in the Class A, this will never happens.... with high volume of audio entering or low volume of audio entering, class A has always high current crossing output transistors.... audio does that too... self biasing the transistors.

regards,

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg

Last edited by destroyer X; 21st October 2012 at 04:47 PM.
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