help! impedance!

[electro samurai]

can someone plz tell me what is this circuit's impedance?

[Frank Berry]

The LM1876 can drive either a 4 or an 8 ohm load.

[electro samurai]

oh, oops...i ment input impedance

[Frank Berry]

I don't find any information about input impedance.
It's high.
What are you planning? Why is imput impedance important?

[djk]

If you read the manufacturers data sheet on this part you will find:

http://www.national.com/ds/LM/LM1876.pdf

You are missing a whole bunch of parts to make it work right.

The input resistor is suggested to be 47K

The zobel is 4R7 + 0.1µF

The damped coil for driving capacitive loads is 0.7µH + 10R

[Frank Berry]

"If you read the manufacturers data sheet on this part you will find:"

His attachment came from the manufacturers data sheet.

As I asked in my earlier post, what are you planning? Why is input impedance important?

[GregGC]

The imput impedance will depend on the resistor you put to GND from +in. You need it in order to provide a Ibias for +in. It can be from 1k or less to 1meg if you want but most likely from 20k to 200k (the circuit you have in the zip file has no DC gain). The best way is to determine what kind of Rin you need and than connect a resistor with that value there. If you're going to use a pot and no input cap than the input impedance will be determined by the pot.

Hope it helps.
/Greg

[djk]

"His attachment came from the manufacturers data sheet."

The data sheet runs to ~20 pages. The drawing he linked to is CONCEPTUAL, meaning it WON'T WORK properly without additional parts.

If you would bother to read the drawing marked 'typical audio circuit' you will see that it has more parts.

Not only that, but there is an explanation of what each part is/does.

If you can be bothered to read the WHOLE data sheet.

[electro samurai]

Originally posted by Frank Berry
I don't find any information about input impedance.
It's high.
What are you planning? Why is imput impedance important?

a guitar amp.
i think guitars have 1M impedance.

[i]Originally posted by djk
If you would bother to read the drawing marked 'typical audio circuit' you will see that it has more parts.

oh...i kind of copied the 'typical audio circuit'...so i think u might find them v-e-r-y similar.

about the in+ to gnd resistor, ive seen a guy who built this, with no such resistor, he claims it sound great.

i renewed it.
what do u think?

[HDTVman]

Try looking at the "Auxiliary Amplifier Application" This gives a more complete schematic. Read the ENTIRE APP. NOTE if you want to know what the manufacturer recomends. You will find the answer if you look for it.

Later BZ