Buffers with output impedance like an amp???

[Bill Mountain]

So...since SS amplifiers can have super low output impedance...can a buffer (opamp or discrete) be built to match the output portion of a power amplifier in order to get super low 4-16 ohm output impedance from a buffer???

Is this a pipe dream?

[Seljer]

This may be what you're envisioning http://sound.westhost.com/project56.htm

You add current feedback to your regular amplifier topolgy so acts if you had a couple of ohms out impedance, without there actually being any extra losses. A lot of SS guitar amps do actually use this topology.

[Bill Mountain]

This is a great read but I'm unclear how to apply this to use as a buffer.  I'll use what I learned in this article to do some more research.

Thanks!

[Seljer]

Ah, I've reread your post and i'm not sure if I understand you correctly, you want the opposite?

Thats the entire reason why we use opamps and feedback. Through the magic of feedback, if you put in a 1V input signal, you get 1V at the output, no matter if you've got 1000kilohms or 100ohms load connected, so in essence, 0 ohms internal impedance. The feedback compensates for any extra current the load may draw (provided that your load's impedance isn't too small)

[Bill Mountain]

I agree with you except that the in the real world an opamp DOES have an output impedance.  I don't know what it is but I've heard some say it can be as little as 10 ohms and as high as a 100.

I have no practical circuit in mind but say I was driving a hypothetical super impedance sensitive EQ circuit with a 100 ohm load how could I guarantee the lowest output impedance of a buffer circuit?  Would I use an opamp and assume it has a zero output impedance or does a circuit exist that will guarantee me <10 ohm output impedance?

I figured since amps consistently drive such small loads that there was a part of amplifier topology that could be adapted to buffer use.

Or am I over thinking it again?

[Gus]

You need to think about available output current from the opamp

CLOSED LOOP output impedance with an opamp means little when you are driving a  lower ohm load with a opamp

A power amp is often like a big opamp with greater current output both source and sink

Use ohms law for the needed current 100 ohms at what voltage?

1V 100 ohm      10ma
10V 100 ohm    100ma

Look at data sheets for opamp current output specs

[Bill Mountain]

Thanks.  That makes complete sense.