Input signal distortion.. capacitive coupling?

[Jamie]

MRW wrote:




Avoid using them at all costs for audio especially. Few worse op-amps have ever
been made.

Graham

Before condemning a component that is and still is being used to this day
in the newer packages, you should do your home work.
We have lots of industrial controllers that use that chip, simply
because of it's characteristics which plays a key roll in the operations
of the device.
Every thing has it's place! including you and this isn't one of them!

 

[Chris]

It is pretty simple, in concept. One glob of transistors
constitute the "pull up" system (that provides a current
path from the positive supply rail to the load) and another
glob of transistors constitute the "pull down" system (that
provides a current path from the load to the negative supply
rail). If both these systems are partly on, when no load
current is needed, this produces a current path from the
positive supply rail to the negative rail, draining power
from the supply, continuously. This is called class AB.

But it allows the amplifier to switch from pull up to pull
down, very smoothly, by just increasing the pull down
current while simultaneously reducing the pull up current
(or vice versa). The LM324 was optimized for very low
drain, battery operation, so instead of class AB, they set
it up so that, at idle, neither pull up or pull down is in
operation, so the output stage draws no current. But it
takes a little time to get the pull up or pull down system
operating, once either is needed. This dead time represents
a chunk of the output waveform that is malformed, and is
called cross over distortion (when the output current
crosses over from positive to negative, or vice versa).


Yes. It simplifies lots of aspects of most circuits. Once
you understand these fewer aspects, then you add the details
that let the system operate from one supply.


I am talking about your education, not your final circuit.

Mr. Popelish's suggestion can be inplemented this way with one 9V
battery:

| .--------o-----------------.
| | | |
| | .-. |
| | | | |
| | | | |
| | '-' |\|
| | Vcc/2 | -|-\ Vo
| --- o | >---o
| - | -|+/ |
| | .-. |/| .-.
| | | | | | |
| | | | | | |
| | '-' | '-'
| | | | |
| '--------o-----------------o----o
|
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
(some of your circuit details omitted)

You've got the divider for Vcc/2, and your LM324 output doesn't cross
over from sourcing current to sinking current (something the LM324 is
spectacularly bad at). Since it's always sourcing current, no
crossover distortion. Done.

Good luck, and keep thinking. I'd recommend spending more time on the
data sheets and manufacturer app notes. They're a gold mine of basic
as well as esoteric information.

Good luck
Chris

 

[Bob Masta]

. A friend of a friend once told me that "once you know how to
deal with high frequency stuff, then the equations used for them will
also apply to the lower frequency counterparts." So I've decided to
also look into Smith Charts and S-Parameters to start things off. I
haven't quite gotten the big picture, yet, but I'm starting to put
puzzle pieces together.

Well, not to pick a fight with your friend, but my advice would be
to forget about Smith charts and S-parameters for a while,
unless you really need to do RF work. I'm not saying that he's
wrong, just that in general the RF world has to deal with a lot
of stuff you don't need to worry about at lower ("audio") frequencies,
like transmission line effects.

On the other hand, the Smith graph paper is a work of art
in itself. Maybe just have a sheet framed and hang it on the
wall, then ignore it until you need it. Sorta like a fire axe
under glass.... ;-)

Just my 2 cents' worth...




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
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