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Old 28th October 2012, 09:36 AM   #61
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by destroyer X View Post
.............The ones watch my videos knows we can put out, at least 4 watts RMS because of 20% efficiency in class A operation.................
This is complete fiction !

A Push Pull ClassA output stage has a theoretical 50% maximum efficiency when the output is at the theoretical maximum.
eg.
with 20V supply rails and a theoretical perfectly lossless output stage the maximum output is Vpk=Supply Rail voltage.
The theoretical maximum ClassA current is = twice the output stage bias current.
Let's set the bias current to 1A.
The theoretical maximum ClassA output current is 2Apk, twice 1A bias.
The theoretical maximum ClassA power is 20Vpk * 2Apk / 2 = 20W
The supply rails are supplying 1A @ +-20V. The quiescent power dissipation of the idealised output stage is 40W.
The idealised efficiency is 20W/40W = 0.5, i.e. 50%

You cannot invent a 20% figure for efficiency and try to con Members into believing you are correct just because you stuck that rubbish in a video.
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Old 28th October 2012, 12:16 PM   #62
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Default Well boys... Mr. Andrew is always very fast, and efficient, to bring bad news

He is right... power is only 1 watt.... in pure class A, but this is not a tragedy, as we can increase bias (double) and then we will have 2 watts each channel and this is much more than we need to a civilized and confortable audition, in special classic music during the "pianissimo" moments.

1 watt per channel is fine too, as we gonna have 2 watts and this was tested down the seventies by some famous designers and considered enought.

So, we have what is enough, sadly with a very low efficiency.

You can reduce your bias settings to 70mA with your trimpot adjust to the maximum, this will keep this level (a little bit bigger than the standard 20mA used to the Dx Blame series of amplifier) till you reach 6 watts, then it gonna be reduce step by step and above 10 watts (till 80 watts RMS) you will have the standard 20 mA current..... we will never supress the DC bias..it will be there all time long.

So, you have three main options i suggest, first is to keep the 250mA per rail bias, this is good and enough and confortable.... heat is not that big and sound is awesome.... you can increase to 500 mA per rail..this is a little bit crazy, but you can if you want, and you can ajust to Class AB operation...so, this amplifier become a three in one... three options in the same amplifier, depending your stand by bias setting.

It is not a Class A amplifier, also it is not a Class AB amplifier, it is the best option i think, as we can adjust the way we want.

Alike the music shown, it is and it is not class A...it looks Class A (till one watt) and then it looks Class AB, but it is advanced bias, increased bias till 6 watts..and them it will be really Class AB.

Enjoy and be happy folks... the best amplifier i have made is now offered to the community to build and enjoy....it is sounding much better than the previous models, and it is playing nice sound with all my 4 speakers...all them cheap units...this is the advantage..to play good sound with cheap speakers... i cannot see advantage to obtain nice sound with 5000 dollars speakers...they do anything more than their obligation to play a nice tone being so expensive.

I am happy, i love to be happy, i am a positive guy and i dislike negative people that only exist to bring us down, or to drive us mad, or to bring bad news and never good news..so... i take as my right not to read or answer people that drives me sad.

About heat... i found it stable...but some guys may face troubles if they use small heatsinks, bad ventilation with heatsinks inside enclosure, or making mistake while adjusting the stand by bias... these ones may need a fan blower to help them.

Adjust it measuring voltage drop into one of our 4 power emitter resistors (220 ohms) to 50 milivolts DC without any audio entering your amplifier.

Play for 10 minutes, do it loud, and then adjust it once again...it should be adjusted while hot..then observe the voltage drop monitoring one emitter resistor...if goes increasing voltage (bias increasing) then increase heatsink, remove cover from your equipment or install a fan.

Here is the final video about the subject...the amplifier is ready... approved!

Enjoy 1W each channel in pure class A and 80 in class AB - YouTube

regards,

Carlos
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Old 28th October 2012, 12:49 PM   #63
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Default Uuops!.... here you have the schematic with small modification in

the VBE multiplier resistors.

regards,

Carlos
Attached Files
File Type: pdf Dx Super A - final with instrum.pdf (58.1 KB, 290 views)
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Old 28th October 2012, 01:45 PM   #64
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Default I was invited to this Brazilian forum

regards,

Carlos
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File Type: jpg Estou num outro forum Brazuca..jpg (472.9 KB, 654 views)
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Old 28th October 2012, 03:23 PM   #65
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Default The unit goes playing all day long

This is the main part of the test... the endurance, a torture.

I am listening to the Dx Super A at 500 miliwatts - YouTube

regards,

Carlos
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Old 28th October 2012, 05:34 PM   #66
AndrewT is offline AndrewT  Scotland
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Default power is only 1 watt.... in pure class A, but this is not a tragedy, as we can increa

Quote:
power is only 1 watt.... in pure class A, but this is not a tragedy, as we can increase bias (double) and then we will have 2 watts each channel
Carlos,
how ?
If the bias is set such that there is 1W of ClassA output power available then doubling the bias current increases the available ClassA power to 4 (four) times.

250mA bias ~= 500mApk of ClassA current & that = 1W of ClassA into 8r0.
500mA bias ~= 1Apk of ClassA current & that = 4W of ClassA into 8r0.
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Last edited by AndrewT; 28th October 2012 at 05:39 PM.
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Old 28th October 2012, 06:16 PM   #67
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Default Here some more informations about insulation voltages and

resistor wattage.

regards,

Carlos
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File Type: jpg Remarks about Dx Super A.jpg (902.7 KB, 588 views)
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Old 28th October 2012, 08:01 PM   #68
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Default Adjustment...i have made a mistake

We must measure 25 milivolts DC in each of the 4 power emitter resistors as voltage drop in stand by mode, no signal entering the power amplifier.

If we have only one pair in the output, then we should adjust 50 mV and check the other power emitter resistor.

Sorry.... i am becoming old...this is happening with me.

regards,

Carlos
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Old 28th October 2012, 08:51 PM   #69
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Default Five Brazilians already built the unit and they said sounds wonderfull

and they just cannot switch off...so good is the sound.... i have also felt this way.. i just cannot switch it off anymore.

I am in two Brazilian foruns, and another one is remote controlled (ahahahaha!)

Two of them forgot the heatsinks to the second VAS transistor (BD139) and to the drivers (BD139 and BD140).... they all need, in special the second VAS.

regards,

Carlos
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Brazilian Airways Christmas Message to all of you!
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Old 28th October 2012, 09:25 PM   #70
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Default We are working together in perfect harmony...me and Juan Vargas

Well...he is producing the layout and i am bothering suggesting modifications.

Soon we gonna have his layout posted here..... we are working hard.

A video will be posted answering questions Juan has made.... if i like the layout or not..then i am bothering asking him to move parts.... he is very calm with me..if was the opposite i would send him to hell with one way tickets..but he is very nice...much more nice than i can be.

Carlos Mergulhão is the words you should type in the Youtube's adress line..then you will be sent to my channel.

regards,

Carlos
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