Dx Blame ST together Dx Super A

I have decided to produce a pcboard with the Super A circuit (transistorized) included withing the circuit board.... so, it will not be an external circuit to connect to the main pcboard with wires or flat cables.

Juan Vargas is producing the layout and this may take several months to be ready...but we have already started.

This is because sonics is fine and there's a lot of guys that loves Class A, despite this Dx Super A is a little bit different... stand by current is smaller and the power while in class A is not that big...but sonics to low levels have really increased in quality (and also a little bit mufled at low levels as class A use to be in my point of view).

Juan and me, we are deciding if we gonna use Mitchel's layout to be modified to if we gonna make (Juan will make) a new one without the use of Mitchel's layout to the Dx Blame ST (green Brazilian group buy ones).

Here you see the first study made by Juan Vargas (Vargas Mongo from Puerto Rico), and in the next post i will show you Mitchel's layout.

Modifications will be the inclusion of the Dx Super A circuit... a couple of transistors, capacitors, diodes and resistors.... just that..but this produces a lot of hard work and take a lot of time if we want to make things simetrycal and aligned.

Here is the first study made by Juan.

regards,

Carlos
 

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Naturally, everyone can produce the layout.... but i will give some

preference to work together Mitchel and Juan, as we are already tuned related a lot of details... you can make even better layout, but it will not be "latine" in it's soul.... this one is "Brazilian" in it's soul... latine but without advertisements printed into the pcboard.

Already have asked Juan to remove his draws, ships, brand names and all advertisement previously present in his pcboards...i want the circuit board clean..only part values printed.... Layout revision by Juan Vargas, Circuit Designer Carlos Mergulhão and Dx Blame Super A.

Circuit will be adjusted to 42 plus 42 volts supplies...power can reach 90/180 watts RMS if you accept some small distortion (8 and 4 ohms)...it will have two output pairs, and we gonna use 2SC5200 and complementary, BD139 and complementary and BC546 and complementary.

I will not make it customized to other voltages and i have no intention to run group buy...but we will give you black and white layout (copper tracks) in order for you to etch at home if you want

I am playing with the Dx Blame with Dx Super A module (published in this forum)... you can see in this video:

.http://www.youtube.com/watch?v=2LvjAba3BZo

There are several videos about Dx Super A.... here you have some:

http://www.youtube.com/watch?v=racP712eFKk

http://www.youtube.com/watch?v=UNsYO3sdECc

http://www.youtube.com/watch?v=QBLUoUXEEM0

http://www.youtube.com/watch?v=Q0x7HJcqtvE

http://www.youtube.com/watch?v=cn4GKxnOmBw

My channel adress is:

http://www.youtube.com/user/destroyersoueu?feature=mhee

regards,

Carlos
 
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Amplifier prototype tested and ready to go

I am uploading videos with testings made...... next week i will explain (again) how this circuit operates.

Here you have the schematic that played full power by 6 hours long...no troubles.

Supply voltage is 42 plus 42 volts

Output voltage is 28VAC RMS at 8,4 and 2 ohms

Power output is 100/200 and 400W RMS

Distortion to 100W at 8 ohms is 0.001% (THD)

Distortion to 400W at 2 ohms is 0.028% (THD)

Sensitivity.... 800 milivolts to full power

Input impedance: 56K aproximately

Stand by current: 250mA

Circuit efficiency is around 55%....so, you need a little bit twice the output power to obtain full power swing... more or less 200VA to 100W, 200VA to 200W and 800VA to 400W (aproximately)

Heatsink should be huge and a fan installed will be a very good idea.

Operation to 2 ohms is critical, so, do not use power transformer above 30 plus 30 volts AC because this will put the output at risk..use the strongest and more modern output transistors you can find...these ones suggested are no good for 2 ohms operation.

Compared to the Dx Blame St i have made modifications...the inclusion of a 1K resistor in series with the first VAS colector, the gain resistor now is 1200 ohms, the input resistor that sets the input impedance is 56K and this will allow you to use 680n capacitors to the input.... maximum is 1uf in the input and please try units with small insulating voltage..do not use big ones to 250 volts or more...better to use 6 volts of insulating voltage there...or even less..capture electrolitic condenser from a junk... small cassete players, small radios.... these ones have small insulating voltage condenser and capacitors due to their supply voltage that is low.

A future video will explain, a little bit more technically, how this circuit works with current charts....i am sure you will understand if you already do not know how the stuff works (i doubt that).

regards,

Carlos
 

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I would like to inform the ones does not know the Dx Corporation

Dx amplifiers are made for you, it is not a business, anything is to be sold, usually offered in group buys and for free to the DIY community ... we provide layout for you to etch at your home and some help... we even explain some basic things we know (only basic things).

The Corporation has not existence in the real world, it is just a name, an Union of audiophiles (the best ones) that loves to build their own amplifiers, tweak and adjust....it is constituted by these guys that usually cooperated producing board layout (I do not know how to do, i do not want to learn how to do pcboard layout, i am unable, i want to continue to be unable and dumb about that) and they usually help in several other ways too.

These amplifier are usually based in Doctor Self designs, in special the Blameless...they are modified, tweaked for sonics and offered as a tested amplifier already built by hundreds of forum folks.... more than 300 units in Brasil and more or less 600 units wide world...all them for free!

I am not an engineer, nor a designer....i am a self made man that loves audio electronics and use to be building audio amplifiers... thousands made (half of them exploded in my face)...my expertise is to force things to work and to build "Franksteins"... using several different designer's stages together.... always build and tested, sometimes tortured...it is something you can trust will not bust in your face.

This one was tested yesterday..the whole day...from 7AM to 8PM.... passed!

I am 52 years doing this stuff (buiding units) and i have made several studies including in Sony Japan but all i know (reality) is due to the practical exercise of try and error and basic ohms law calculation together imagination, love and passion by audio electronics.

The point is to produce good sound with cheap speakers...there's no point to me to obtain good sound with an acoustic prepared home spending thousands of dollares to buy exotic speakers...i want good sound playing with standard, general, common speakers...cheap ones...and to make my units not spending too much money for it.

These last years i had several good guys helping me.... Daniel from Croatia (now a days a pipe maker), a lovely dutch that make beer can, an awesome engineer that produces hand made layouts (Taj), a Oil man from Petrobrás, Miguel Nabuco (Mitchel), an expert in computers from Germany (Rudi), a guy filled with passion by audio from mid east (Metal), a clever brazilian from São Paulo (Herman), a kind guy from Puerto Rico (Juan) and several many others that gave me a hand and i have to thank all them by the enjoyment to work together people that has passion for audio.

regards,

Carlos
 

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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
 

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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
 

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  • MJL4302A e MJL4281A.pdf
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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
 

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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
 
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?
 
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
 

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  • Dx Super A - MKII.pdf
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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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