I was fairly interested in electronics when I was in high school. To
the point where I built several kits including a COSMAC Elf 1802
computer. However, I strayed from the hobby over the years but am
slowly returning. Now I am challenged by OpAmps and negative voltage.
I do not understand how to generate a negative voltage (for
differential inputs) from one power supply such as a car battery. I
am trying to build a small headphone amplifier and am just coming up
with noisy audio. I believe this is because I am not apply the
negative voltage correctly. help!

a_w_abate,

To the point where I built several kits including a COSMAC Elf 1802
computer.

Wow, that was my first computer too. I recall being quite excited when I
entered a sample program that filled a 16 bit register the did a loop of
decrements and turned on a little LED when it was finished. It took about a
second. I would have bought/built something more complex / complicated if I
had the loot, but as a family man I didn't have any spare cash for such
things.

Now I am challenged by OpAmps and negative voltage.
I do not understand how to generate a negative voltage

Nothing special about a negative voltage. As with all voltage
what matters is the reference. Let's say that you consider
the reference point on a flashlight cell is the negative
terminal, then the positive terminal is at + 1.5 V. Then let's
say you decide that the positive terminal is the reference,
Then the negative is - 1.5 V. With op amps they often use
two power sources, they ground the negative terminal of
the positive source, and ground the positive terminal of
the negative. Both supplies may be identical, only the
grounded (power supply common) terminals make them
positive or negative terminals.

(for differential inputs) from one power supply such as a car battery. I
am trying to build a small headphone amplifier and am just coming up
with noisy audio. I believe this is because I am not apply the
negative voltage correctly. help!

If you are using batteries, just connect one with it's negative terminal
as common, i.e. grounded. Connect the other battery with it's positive
terminal grounded. Now you have a common terminal, which does NOT
get connected to the op amp, and a negative supply and a positive supply,
which DO get connected to the op amp.

One feature of an op amp is it's very high input impedance. This is achieved
because of the dual supply. The output impedance is extremely low.
What is really weird is that in some configurations the input at the
actual op amp is actually low. The input impedance of the amplifier then
is equal to the input resistor.

Please don't anyone flame me on my op amp knowledge or lack thereof.
I haven't worked with them in awhile.

Jim

Try this:

+
|
R
|
*---||--------- Opamp Input
|
R
|
-

Did you understand that ? I sure didn't :). The point with the
negative voltage is to allow the audio signal to swing both ways Now
if you're able to put the audio signal to swing around 6V instead of
0V, then you can just use the 12V car battery without a negative
voltage.

Use for example two 1K resistors. One between Vcc and opamp input,
and one between opamp input and GND. Connect the opamp input VIA A
CAPACITOR to the audio signal source.

I think that should work

Mounir
--- In Electronics_101@y..., a_w_abate@y... wrote:

I was fairly interested in electronics when I was in high school.

To

the point where I built several kits including a COSMAC Elf 1802
computer. However, I strayed from the hobby over the years but am
slowly returning. Now I am challenged by OpAmps and negative

voltage.

I do not understand how to generate a negative voltage (for
differential inputs) from one power supply such as a car battery. I
am trying to build a small headphone amplifier and am just coming

up

with noisy audio. I believe this is because I am not apply the
negative voltage correctly. help!

开云体育