Building Class AB Amplifier Do I Need Some Changes??

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#61
WhiteDragon said:
Sorry been gone, long week at work.
I also have received a gift.... a lovely tooth ache. time for dentist

Amplifier posted in post #59
Is very common topology
But is missing a few elements.

Also as noted before, it is using diodes for bias.
This can be done , and does mention they must be mounted
on heatsink to thermal track.
Bias is preset with resistor, so as suggested before is better to make bias adjustable.

Then again most stay away from diode thermal tracking
and I would do same modification as last amplifier.
Would use VBE multiplier and have trimmer potentiometer
for bias adjustment.

Q3 and Q4 is current mirror.
Keeps current balanced for
Q1 and Q2
this will lower distortion and also improve slew rate.
it will also increase open loop gain.
without re writing the book on basic amplifier theory.
C4 value must be correct for stability with changes to open loop gain.
Without calculation, just from experience C4 likely needs to be
slightly larger around 100 to 120p

Q3 and Q4 in schematic do not have degen emitter resistors.
Depending on current set by Constant current source Q5
Emitter resistors need to be added, and the value depends
on current. Your looking for a 60mV to 100 mV voltage drop
across emitter resistors. transistors slightly vary
and is important to have emitter / degen resistors for current mirror


Q5 current source seems to be set low around 600/700 uA
probably about right for GM
But Q6 second gain stage or VAS is simple single transistor.

I would probably raise Q5 current to 2 or 3 mA
Then add degeneration resistors to Q1 and Q2 as well.
To get GM back to where it should be.
But now have extra current overall for Q1 and Q2
to drive 2nd gain stage Q6.

Again without re writing amplifier theory
usually good degen resistor value would be similar
value used for Current mirror degen.
This of course all depends on what the current source
is set to.

with single pair output transistors, very similar to previous
amplifier. suggest around 30 to 35 volts +/-
Click to expand...
No Need To Say Sorry Its Ok Brother And Thank You So Much For Giving Us Your Rare Time... As u Said About Is A Very Simple Topology I Agree There Should Need Some Changes..I Will Work On it As U Guide Me..Now I Am Going Very Deeply To The Basic Things Of Amplifiers Just Bcoz Of U. You Taught Me Very well As A Teacher... Once Again Thaks White Dragon..
And Don't Go Any Where Bcoz When I i will feel Trouble in things Related To Amplifiers I Will Request You to Firstly For Helping Me..
Any If You Need My Help Any Time In The Life I Will Be Available For You Always For Helping You..
and Sorry For My Bad English...
Now I Am Able To Make My Own Amplifiers Designs... It Is Truth Just Bcoz Of You..☺
 
#62
Zohaib Ahmad said:
No Need To Say Sorry Its Ok Brother And Thank You So Much For Giving Us Your Rare Time... As u Said About Is A Very Simple Topology I Agree There Should Need Some Changes..I Will Work On it As U Guide Me..Now I Am Going Very Deeply To The Basic Things Of Amplifiers Just Bcoz Of U. You Taught Me Very well As A Teacher... Once Again Thaks White Dragon..
And Don't Go Any Where Bcoz When I i will feel Trouble in things Related To Amplifiers I Will Request You to Firstly For Helping Me..
Any If You Need My Help Any Time In The Life I Will Be Available For You Always For Helping You..
and Sorry For My Bad English...
Now I Am Able To Make My Own Amplifiers Designs... It Is Truth Just Bcoz Of You..☺
Click to expand...
I only know English, so it is great accomplishment for you to know 2 languages

This forum is full of very helpful people I have learned much as well from other members.

Maybe for more details I suggest reading Bob Cordell Website https://www.cordellaudio.com/
He is also member of diyaudio
Very informative Books he wrote http://www.cordellaudio.com/book/

Also Douglas Self and his website http://www.douglas-self.com/index.htm
He is also member of diyaudio
Has books available as well http://www.douglas-self.com/ampins/books/apad.htm
also information on power amplifiers on his website http://www.douglas-self.com/ampins/dipa/dipa.htm


I also suggest learning Spice Modeling
So you can build and test / modify amplifiers in simulation.

I use Tina TI from Texas Instruments https://www.ti.com/tool/TINA-TI

Download is free, just need to register with Email very simple.

First schematic I build for you is working Tina Ti model actually.
You can build your own models, or I can give you already built working models.
Of course a small learning curve.
Basically you can build circuit and test with common bench tools.
Function Generator, Oscilloscope, Voltage/Current Meters
and Distortion analyzer. Real life very expensive.
In simulation all free
 
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#63
Th
WhiteDragon said:
I only know English, so it is great accomplishment for you to know 2 languages

This forum is full of very helpful people I have learned much as well from other members.

Maybe for more details I suggest reading Bob Cordell Website https://www.cordellaudio.com/
He is also member of diyaudio
Very informative Books he wrote http://www.cordellaudio.com/book/

Also Douglas Self and his website http://www.douglas-self.com/index.htm
He is also member of diyaudio
Has books available as well http://www.douglas-self.com/ampins/books/apad.htm
also information on power amplifiers on his website http://www.douglas-self.com/ampins/dipa/dipa.htm


I also suggest learning Spice Modeling
So you can build and test / modify amplifiers in simulation.

I use Tina TI from Texas Instruments https://www.ti.com/tool/TINA-TI

Download is free, just need to register with Email very simple.

First schematic I build for you is working Tina Ti model actually.
You can build your own models, or I can give you already built working models.
Of course a small learning curve.
Basically you can build circuit and test with common bench tools.
Function Generator, Oscilloscope, Voltage/Current Meters
and Distortion analyzer. Real life very expensive.
In simulation all free
Click to expand...
Thanks White Dragon For All The Links I Have Already Downloaded All PDF Books.. These Books Are Very informative..
And I Also Download The Tina T1 After free Registration It Is Excellent Software For My All of Projects.. It Will Save My Lot Of Time And Money In Future...
Now I Am Trying To Learn About Lt Spice or Tina T1..
in the recent Days When I worked On An Amplifier Or Repair An Amplifier Or Just Built It Through Schematics It Takes My Several Days😥... And I Also Spends Lots Of Money On It Bcoz I Have No Idea Before That I Should Firstly Simulate Amplifier Design In Simulation Software And Then I Should Built It To save My Lot Of Time And Money.
But After Coming On Diy Other Members And You Specially Helped Me A Lot And Taught Me Well Thanks All Of You..☺
As U said You Have Working Models of Amplifiers Can U Provide Me The Schematics Of Working Models That You Have???? Which Works Aproximately With +-30v DC to +-35/38DC or +-48 dc to +-55/60v dc..
Once Again Thanks For Your Rare Time.. 👍🏻
 
#67
katiyar said:
I think this schematic is similar to been developed by Video Rockola in past.

Also the bias section need improvement. With the present arrangement bias current will surely vary with rail voltage and temperature and it would probably be not possible to keep the bias current within a suitable range. In my openion VAS and driver transistors need to be replaced by better transisstors like KSC 3503 and KSA1381 having very low Cob. I donot think TIP and MJE 340/350 transistors are suitable for VAS.

If you want to build an amplifier with no bias current adjustment with much lower distortion and excellent sonic quality audio, my advice is go for Elvee's Circlophone. https://www.diyaudio.com/community/threads/my-little-cheap-circlophone-c.189599/
Click to expand...
Yes this is very interesting amp but I am confused with schottky diodes or bat diodes...
I wanted to build this amp but can I use
1n4007 or above diodes instead of schokty diodes or bat diodes????
It may be helpful if these diodes are interchangable..
 
#68
Zohaib Ahmad said:
Yes this is very interesting amp but I am confused with schottky diodes or bat diodes...
I wanted to build this amp but can I use
1n4007 or above diodes instead of schokty diodes or bat diodes????
It may be helpful if these diodes are interchangable..
Click to expand...
No. They are not interchangeable. 1n4007 drops .6 to .7 v, schottky diode drops .3 to .4 v. BAT48 is one available type of schottky diode. If you have a blown switcher power supply like a ATX supply for PC, they are full of big double schottky diodes. Not as small as a BAT but they are free, on the way to the dump.
 
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#69
indianajo said:
No. They are not interchangeable. 1n4007 drops .6 to .7 v, schottky diode drops .3 to .4 v. BAT48 is one available type of schottky diode. If you have a blown switcher power supply like a ATX supply for PC, they are full of big double schottky diodes. Not as small as a BAT but they are free, on the way to the dump.
Click to expand...
Thanks sir for answering and also for Guidness. It is very difficuilt to to find out schottky diodes here. Even they are not used now a days here. But I will try to find out them for the making of this amplifier..
 
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