Krell KSA 100 schematic, resistor value question
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Tube_Dude
diyAudio Member

Join Date: Mar 2002
Location: Aveiro-Portugal
Quote:
 Originally posted by millwood I thought it was settled on that other thread that for such a topology, you cannot calculate VAS and LTP current. Assuming that the current in the LTP legs is evenly split is falwed. hopefully, the time and effort there were not wasted.
The time and effort were never wasted in good company!!!

Were your simulation is flawed is:

The bases of the input LTP are not grounded in the real circuits...(i prefer real circuits that simulated ones)...and in the case of the Krell they are connected to ground by a 22 KOhm resistor.

This is reflected in the emmiters of the LTP as as 220 Ohms + the 220 Ohms emmiters resistor ..become 440 Ohms...

So any small diference in the Vbe of the LTP become with no consequence!!!..and the current will be splited almost evenly in the LTP.
__________________
Jorge

millwood
Account Disabled

Join Date: Apr 2003
Location: US
Quote:
 Originally posted by Tube_Dude The time and effort were never wasted in good company!!! Were your simulation is flawed is: The bases of the input LTP are not grounded in the real circuits...(i prefer real circuits that simulated ones)...and in the case of the Krell they are connected to ground by a 22 KOhm resistor. This is reflected in the emmiters of the LTP as as 220 Ohms + the 220 Ohms emmiters resistor ..become 440 Ohms... So any small diference in the Vbe of the LTP become with no consequence!!!..and the current will be splited almost evenly in the LTP.
someone had pointed out in the other thread that none of the above will change the nature of the circuitry: it is not determinate, "almost evenly" notwithstanding,

Tube_Dude
diyAudio Member

Join Date: Mar 2002
Location: Aveiro-Portugal
A lucky bias...

Quote:
 Originally posted by millwood someone had pointed out in the other thread that none of the above will change the nature of the circuitry: it is not determinate, "almost evenly" notwithstanding,

The bias in the krell is indeterminated!!
Is set by luck!!
__________________
Jorge

 19th February 2004, 04:06 PM #24 Eva   diyAudio Member     Join Date: Oct 2003 Location: Near the sea millwood : I recommend you throw some transistors at a breadboard and test by yourself this biasing scheme in an empirical way Anyway, this topology is reliable since it's the one choosen for most consumer discrete amplifier circuits today
Elso Kwak
Banned

Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Bias Circuit

Quote:
 Originally posted by millwood someone had pointed out in the other thread that none of the above will change the nature of the circuitry: it is not determinate, "almost evenly" notwithstanding,
Hi Millwood,
I see an amplified diode or VBE multiplier as in Ritchies book: Transistor Circuit Techniques, Chapman & Hall, page 160.
Not determinate?????

Tube_Dude
diyAudio Member

Join Date: Mar 2002
Location: Aveiro-Portugal
Re: Bias Circuit

Quote:
 Originally posted by Elso Kwak Hi Millwood, I see an amplified diode or VBE multiplier as in Ritchies book: Transistor Circuit Techniques, Chapman & Hall, page 160. Not determinate?????
Sorry...i'm not Millwood...but he talk about the current in the VAS stage...and the VBE determine the current in the output stage...
__________________
Jorge

 19th February 2004, 05:32 PM #27 millwood   Account Disabled   Join Date: Apr 2003 Location: US it is not determinate because you cannot calculate it without assuming the current going through at least one leg of the LTP, or vis versa. that's why simulated results are so widely apart from each other. I was hoping that service manual will have specified the current so we know for sure what it is.
 20th February 2004, 02:59 AM #28 MikeW   diyAudio Member     Join Date: Sep 2002 Location: North of Boston bias? Has anyone built one of these and measured the bias? __________________ MikeW
 20th February 2004, 04:44 AM #29 jcx   diyAudio Member   Join Date: Feb 2003 Location: .. the point of the uastable VAS current thread applies with current mirrors in the complementary diff pair collectors - the high output impedance provides a very large voltage gain at the input to the vas which results in a unstable voltage into the vas and indeterminate vas bais current due to the lack of common mode feedback, differential feedback still holds the current division ratio in the diff pairs close to 1:1 in this circuit the 1KOhm resistive collector load provides a very definite and calcuable voltage into the vas and hence a predictable vas bias current (counting on my thumbs i get ~6 mA) with a dc bolcking feedback cap for unity dc gain, dc emitter degeneration and offset trim i think the assumption of equal current division in the diff pairs is pretty good the diff pair current sources could be greatly improved with a couple of bootstrap resistors, the diff pair bypass and feedback dc blocking caps should all be nonpolar/bipolar electrolytics with as high a voltage rating as you are willing to fit

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