Offset Correction using Bias Compensation

[lineup]

Originally posted by Bensen
lineup,

I've been using the midpoint between the two diff pairs, because I don't have a CCS to feed the diff pair.
When you will use a CCS, you can control the current throught the diff pairs with the DC-servo.

See the attached picture to have an idea. I've found this somewere on this forum.

Greetz
Ben

Now, I see you are using a DC-servo feedback circuit, using an OP-amp.
Tthis was not in your circuit before.
I think I saw amplifierguru show somewhere,
how to use correction in between emittors in a symmetrical differential input.

[lineup]

I think I saw amplifierguru show somewhere,
how to use correction in between emittors in a symmetrical differential input.
Here it is with his diagram:
http://www.diyaudio.com/forums/showt...815#post799815

It is from the topic: To use DC servo or not?
I belong to those who do not use DC-servo.
I know it is theoretically a more safe method, especially without input capacitor.

I always use a DC-blocking cap at input.
Yes, in some of my amplifiers even Output DC-blocking Capacitor
which makes DC-offset very much less of a problem!


Even those that does not use output cap, in fact in 49 cases of 50,
use an output cap to at least the tweeter in loudspeaker.

First and second order x-over uses 1 capacitor.
Higher order can use several caps in series.

3-way system use capacitor(s) to midrange woofer and tweeter.

Using active filters makes use of same number of coupling capacitors.
Big difference here is using resistors instead of inductors.

What about an inductor in signal rail. Well most of us use it!
Have a look at a typical LSP crossover high-pass filter.



.... and they think their system is truly DC-coupled

[Bensen]

Lineup,

You understood me wrong. In the schematic from post #6, "V7" is supposed to be a DC-servo circuit. But I just didn't draw the hole servo systeem.

Yes, "P1" is there for to compensate the DC-offset.

[lineup]

okay
I misunderstand sometimes. Give me for

anyway, this compensation trick is something i still use
when working with bipolar input transistors

JFET input has almost zero Bias Current