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Old 10th November 2008, 05:57 AM   #11
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Charlie,
right, I am cautiously optimistic. Nice shirt anyway, but no tie.
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Old 10th November 2008, 07:43 AM   #12
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Default Good way to call your non optimistic moment.


ahahaha.... cautious optimistic... your therms, the way you twist the reality is wonderfull...ahahahahah!

I was remembering... recall.... "Lippy the Lion and Hardy Har Har"

great!

I have increase my Dx Standard bias to 800 miliamperes to listen..... oh pain!.... what a hell awfull sound..... without life... alike my non coloured picture.

Was you that sent me this optimistic energy dear Lumba?

I have used 3 volts RMS into the peaks.... operating class A... aaagh!

I do not know why i use to insist to try class A.... i think i am a very big, enormous idiot... loosing my time.

But will try to fix.... just a battle... war not lost yet!

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
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Old 10th November 2008, 07:50 AM   #13
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Carlo,
you have built plenty of amplifiers based on this topology, haven`t you. Why are the prospects more favorable this time?
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Old 10th November 2008, 07:58 AM   #14
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Default I am thinking to increase the transistors speed


To use faster ones and low capacitance VAS.... to reduce Miller capacitors and feedback capacitors...to have good response into 300 Kilohertz... all that to be sure no problems to audio band high frequencies.... when we have 300 Kilohertz maximum into 3 dB... results less distortions into the audible range... sadly...because this frequency response is also an oscilating addicted circuits too.... because very obvious reason...if it can work (audio is also oscilation)...if can amplify 300 Kilohertz... for sure can oscilate into this frequency too... and our transistors, modern ones, goes easy to 100 Megahertz.... this is very problematic...because there are oscilations triggered by the audio...you see waving over the traces into the scope...superimposed oscilations..lower level but they are there.

Capacitances and inductances you have into the board copper lines (parasitic capacitance) ... distances you have from transistor leads (capacitance)... copper lines near others (capacitance)...copper lines longer than 5 milimeters (inductances).. and we have miliohms of resistances too.... so... we have some "tuned circuits" into boards.... Tank circuit..oscilating devices when you have associated capacitances and resistances...and this exists into boards, components, and leads... so... if you face, lets say.... small capacitances alike 3 picofarads (this is half inch, two legs wire, 1 milimeter diameter twisted one over the other...or some copper lines in parallel... 2 inches ones!... them you have the condenser.... other circuit parts will "produce", will "behave" alike inductances...then ready!...you have an oscilating system... the RF tank circuit oscilating into Very High Frequencies..upper 100 megahertz... and transistors beeing able to do that..for sure they will do!

Also using emitter resistances you can increase treble.... reducing input condenser, limiting low end to have 3 dB less into 20 hertz (this is considered flat) you will perceive the unit as having more mids and trebles (Psycho acoustic effect...brain effect... ratio of tones loudness).

The way we have to reduce crossover distortion is to increase bias to class A.... and it is a good idea to have class A into the power you usually use to play your music (maximum of 2 watts RMS each channel i could perceive).

Class A amplifiers are very hot... and do not have power...so..if you switch from class A to AB you gonna have power... this way you join both "worlds" together..... bring "Greeks and Troyans happy" and may listen something sligthly better than good sound.

What moves me?.... passion and foolish... alike everybody in this forum (majority)

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
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Old 10th November 2008, 08:24 AM   #15
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Default No... i do not use to drink.... even straigth lines are inductors


In the reality straigth lines does not exist... it is a concept inside human brain.... a line is a sequence of interrupted dots.... lines goes turning curved, bouced, rounded... straigth lines into our Universe does not exist..if you trace a line from your town to the nearest town it will be a curve over the globe...... globe is rounded, so lines over it are rounded too... we have gravity... into the Universe we have gravity from everywhere, this turns straigth line impossible... even the black hole forces ligth to became rouded ... ligth does not propagate straigth.

So... your piece of copper line into a pcboard is a very small inductor...BUT... can be combined with others in series and parallel and produce an interesting value of inductance..and this one associated with capacitances creates all the mess.

Every two pieces of metal, placed near together, even having air gap between them... will result into air cores capacitors.

I do not use to drink.

Hic!

Carlos
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Old 10th November 2008, 08:37 AM   #16
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Carlos III,
Quote:
I am thinking to increase the transistors speed
A very wise policy.

Quote:
..if you switch from class A to AB you gonna have power... this way you join both "worlds" together.....
I`m less optimustic about that one. Hopfully, it will not mess up things too much.
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Old 10th November 2008, 09:16 AM   #17
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Default Thank you Lumba.... in the reality i do not think different


I have just some hopes... this moves me.... hope!

Well..... how the circuit works:

First the circuit has a normal VBE multiplier circuit to adjust bias, can have a trimpot and so on... this one has a NTC.... a resistance that is reduced when receive heat... into the position it is assembled....it will reduce the resultant resistance into the BD139 circuit... the main bias control, the manually adjustable one.

Other transistors are receiving audio rectified...so.. they receive DC that changes their operational point.... when iddle you adjust current to .... let's say....hummmm...600 miliamperes... and when you increase the audio output volume... power increasing, then you will have DC enougth to drive the transistors that will reduce resistance from colector to emitter.... this reduced resistance will reduce bias...so...having audio level...bias is reduced.. this way you will go to Class AB operation.

Boys... circuit is not mine...i can adjust it, tweak it, make mine modifications, decide other currents, decide different thresholds ..but it is from JVC...i am just using it as a non profit amplifier, opened to the public, a genuine DIY amplifier, using the technology we have in our world, offered into the internet, opened wide world to everybody.

So... the qualities or defects of this circuit is not my responsability and also does not represents i am a great designer.... i have not made this one...my value is as a tweaker.. the one work hard and burn fingers...i have not created this one.

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
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Old 10th November 2008, 09:29 AM   #18
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Default Bias circuit behaves alike a resistance...you have the main current to be used into


The VAS colector to emitter junction.... this current is adjusted by the bias circuit... even a single resistance can do this job for you.

This VAS colector to emiter current will be modulated, will variate and will be sent to drivers and output transistors.

So... the bias circuit, transistorized or not, is the one provides current to the VAS.

But also, and more interesting, it adjust a DC potential into it's extremes...when current crosses this resistance it develops voltage... and this voltage use to be 2.4 volts into my kind of outplut circuit..the one i use (not discovered by me .... of course).

Into my output circuit... a very used one... Doctor Self use and a lot of folks use this one..emitter follower...or darlington output.... well..you need to set 0.6 volts to each transistor (around that..from 500 to 640 into AB amplifiers.... and more into Class A amplifiers... and lower into class B amplifiers..those one uses almost nothing as bias).

As each upper output line transistors (NPN) are two...then you need 1.2 volts (0.6 plus 0.6).... and the lower transistors (PNP) also will need 1.2 volts (0.6 plus 0.6)... this means 2.4 volts must be developed into this bias circuit..the bias resistance...it behaves alike a resistance...the obligation is to develop 2.4 volts and into the decided current needed to the VAS to drive the output circuit.

Why 2.4 volts and not positive 1.2 Volts and negative 1.2 Volts.

That idea of positive and negative depends your reference..if your reference is zero volts (output line...you have there milivolts, almost nothing)..then you split those 2.4 into two parts..and the polarity will be given because the base to emitter junctions connected to the output line that will create the 0.6 plus 0.6 zener effect because of semiconductors junction.

If our reference was 1 positive volt..then you gonna have positive 0.2 and negative 2.2 volts... all depends the reference..nothing born negative or positive....there are not red positive electrons and blue negative ones...they are all negative into the atom

All the work is this one.... this "resistance" can be something that reduces it's resistance when receiving heat from the heatsinks.... and this will be usefull to control the amplifier...if not... the transistors turns hot and current increases.... when the current increases it turns more and more hot.... this make the transistor internal resistance to reduce and the current increases even more...this goes this way till the destruction....so...if the bias can reduce its resistance (reducing bias), will protect the amplifier.

This is very easy... dedicated not to Engineers or advanced guys.. this is for beginners only...to help you my dear Mr. Incognitus.

No one explains nothing... they think everybody has born already knowing everything... this is not truth... there are a lot of folks, alike me, that need some informations to evolute.

regards,

Carlos
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Old 10th November 2008, 11:38 AM   #19
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Default To the ones interested...as 300 hit seems a good interest into 2 days


Will explain the equivalent circuit attached.

This is the equivalent circuit.... made with resistances.

You can use resistances... they will make the job...not the dinamic job, but they will fix your current into 600 miliamperes (around that), and will feed each transistor with 750 milivolts (if they share the same ammount..normally they do not share the same ammount)

regards,

Carlos
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Old 10th November 2008, 11:44 AM   #20
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Carlos,
as hinted, I am extremely suspicious about that kind of trickery, usually doing more damage than good. Those Engineers are told to invent things by Sales Directors, Compliance Officers and other Functionaries but freelancers like we take no orders.
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