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Old 11th February 2003, 04:15 AM   #1
ward is offline ward  Taiwan
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Default Amplifier design knack ???

Hi all

Any body can comment on several design knack as attached schematic ?

1.What is the purpose of R34 which is 562 ohm resistor connected between B and E of driver stage transistor ?

2.What is the purpose of R36 and R37 which are 56.2 ohm resistors connected between B and E of output state transistors ?

3.How to determine these two resistor value properly ?

Appreciated for any input.

ward
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Old 11th February 2003, 05:36 AM   #2
halojoy is offline halojoy  Sweden
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Default Re: Amplifier design knack ???

Quote:
Originally posted by ward
Hi all
Any body can comment on several design knack as attached schematic ?
1.What is the purpose of R34 which is 562 ohm resistor connected between B and E of driver stage transistor ?
2.What is the purpose of R36 and R37 which are 56.2 ohm resistors connected between B and E of output state transistors ?
3.How to determine these two resistor value properly ?
Appreciated for any input.
ward
I recognize the schematic, as from an Elektor Amplifier.

It is a way to direct some current running.
It will run like I=0.650V/R, through those resistors.
But why?
I think someone else have to answer.
Think reasons can be more than one.

Anyway those resistor raise the current in driver transistors
to more than what is needed to drive the output transistors.
And that can make the drivers operate better - more linear.

/halo - interested to read the answers
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Old 11th February 2003, 08:22 PM   #3
halojoy is offline halojoy  Sweden
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Default Re: Amplifier design knack ???

Quote:
Originally posted by ward
Hi all
Any body can comment on several design knack as attached schematic ?

1.What is the purpose of R34 which is 562 ohm resistor connected between B and E of driver stage transistor ?

2.What is the purpose of R36 and R37 which are 56.2 ohm resistors connected between B and E of output state transistors ?

3.How to determine these two resistor value properly ?
halo & ward
is still waiting for the correct answer
from the "amplifier expert panel"
-------------------------------

Maybe jcarr and the others are just out for lunch

/halo - eats his lunch alone at home
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Old 11th February 2003, 08:45 PM   #4
ststone is offline ststone  United States
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Default Elektor / Elektuur

Yep, I see some TUN's, TUP's, and maybe a DUG.
Live was so much simpler than.
I loved to get those juli/august numbers with over a hundred things to do with a soldering iron. Lots of (crappy) electronic potentiometers.
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Old 11th February 2003, 08:54 PM   #5
halojoy is offline halojoy  Sweden
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Default Re: Elektor / Elektuur

Quote:
Originally posted by ststone
Yep, I see some TUN's, TUP's, and maybe a DUG.
Live was so much simpler than.
I loved to get those juli/august numbers with over a hundred things to do with a soldering iron. Lots of (crappy) electronic potentiometers.
Those old years of edition had really something on transistors.
And you could learn about them.

now, Elektor, I am sorry to say,
have almost only digital circuits, microprocessors and PC-crap
and the audio is mostly IC-based.

Every now and then, there is is a Tube design
but it is very long between the good audio-stuff, nowadays
Even longer time between the interesting discrete designs

/halo - things ain't what they used to be
- and will probably never be .......
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Old 11th February 2003, 09:17 PM   #6
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These resistors are for reducing current gain (make it more predictable), increase the linearity also (I suspect) and also speed up turn off time.

The values of these resistors are like those for gates in mosfet amps, not so critical, certianly not E196 values!
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Old 11th February 2003, 09:18 PM   #7
ststone is offline ststone  United States
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We use to have a very good Dutch magazine.
Audio and Techniek. The minute I left the country the stopped publishing.
The still sell some nice audio kits, mostly hybrids.
A&T
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Old 11th February 2003, 09:32 PM   #8
Previously: Kuei Yang Wang
 
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Default Re: Amplifier design knack ???

Hi,

Quote:

1.What is the purpose of R34 which is 562 ohm resistor connected between B and E of driver stage transistor ?

2.What is the purpose of R36 and R37 which are 56.2 ohm resistors connected between B and E of output state transistors ?

3.How to determine these two resistor value properly ?
1 and 2 and this is with a huge IIRC (If I Remember Correctly) help overload recovery by draining away the saturation charge in the PN Junctions of the Output/Driver Transistors.

I doo seem to remember references to this even in Douglas Selfs stuff, but may be mistaken. So don't quote me on any of this....

Sayonara
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Old 11th February 2003, 10:43 PM   #9
halojoy is offline halojoy  Sweden
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Default Re: Re: Amplifier design knack ???

Quote:
Originally posted by Kuei Yang Wang
Hi,
1 and 2 and this is with a huge IIRC (If I Remember Correctly) help overload recovery by draining away the saturation charge in the PN Junctions of the Output/Driver Transistors.

I doo seem to remember references to this even in Douglas Selfs stuff, but may be mistaken. So don't quote me on any of this....
Sayonara
Yes, both in Self site and Elliot sites,
you can find similar discovery.
In Self site I think it was in the output stage.
-------------
Rod Elliot had a discovery when he tested how to design
the DOZ amplifier.
The Distortion changed when he attched
that b-e resistor to the vas-transistor in DOZ.

I will go search the ESP-article/project.
-----------------------------------------------
Death of Zen A new Class-A power amplifier
http://sound.westhost.com/project36.htm
Elliot say in comment to Figure 3. A test setup:
Quote:
Some interesting things came to light during testing, especially when I included the resistor (R6) from base to earth on Q2. With no resistor, I measured a distortion of 0.15%, and this was almost completely 2nd harmonic. There was a very noticeable degradation of the positive going slope on a 10kHz square wave, and a fairly low slew rate resulted. Adding the resistor improved this dramatically, and reduced the distortion to 0.05% - but it was now almost completely 3rd harmonic.

This will create a conundrum for some - would you rather have very low levels of 3rd harmonic distortion, or considerably larger amounts of 2nd harmonics (bearing in mind that the 3rd harmonics are still there). I cannot see any good reason to tolerate any more distortion than is absolutely necessary, so considering the much better slew rate (and therefore high frequency performance), I will be including this in the final design. You might want to leave it out if you want the 2nd harmonics, but I don't think the end result will be very satisfactory.

This is due to the transistor's turn-on and turn-off characteristics becoming more symmetrical by providing a base discharge path, but I did not expect such a large difference. The frequency response extends to over 100kHz at full power (6V RMS for these tests), and square wave response shows that the amp is both fast and stable - and this with a very ordinary switching darlington. I saw no evidence of measurable distortion above the 3rd - there must be some, but I have no way of measuring it. The 3rd harmonic appears to be an almost perfect sine wave, with some very small variations.
/halo
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Old 12th February 2003, 12:43 AM   #10
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Default Re: Re: Amplifier design knack ???

Quote:
Originally posted by halojoy
/halo - eats his lunch alone at home
Halo, do you have a job to go to, or do you just sit at home all day posting prosaic observations to diyaudio?
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