Recomendation for Hi Input Impedace Op Amp ??

[jalbers@bsu.edu]

I am experimenting with various OP amp circuits based on the 741 . I
know that it is an old op amp but I have a bunch of them and I am not
trying to build anything important right now. Just trying to learn.
For example I have been experimenting with a peak detector circuit
using a single 741, diode, and capacitor. I am using a DVOM with
about 10Meg ohm input impedance to measure voltage drops at various
places around the circuit and seeing what happens. I have a feeling
that the impedance of the DVOM is putting more of an effect on the
circuit than what I would like. I am currencly using a Circuitmate
DM25L DVOM.

I am looking for an OP amp that I could use to make a voltage follower
to boost the input impedance of my DVOM up considerably. I am
primarly experimenting with DC and low frequence AC signals. I would
also like the op amp to be in a DIP package so I can plug it into my
solderless breadboard.

Any help would be greatly appreciated. Thanks

 

[Michael Black]

On Mon, 18 Aug 2008, jalbers@bsu.edu wrote:

I am experimenting with various OP amp circuits based on the 741 . I
know that it is an old op amp but I have a bunch of them and I am not
trying to build anything important right now. Just trying to learn.
For example I have been experimenting with a peak detector circuit
using a single 741, diode, and capacitor. I am using a DVOM with
about 10Meg ohm input impedance to measure voltage drops at various
places around the circuit and seeing what happens. I have a feeling
that the impedance of the DVOM is putting more of an effect on the
circuit than what I would like. I am currencly using a Circuitmate
DM25L DVOM.

You worry too much.

If you were a hobbyist 35 years ago, even more recently, your DMM would
instead be a VOM, an analog meter with if it was a good one 10,000 ohms
per volt, so if you had a scale of ten volts, the input impedance would
be 100,000. Most people lived with such things.

If you paid more money, you'd get a VTVM, Vacuum Tube VoltMeter, that
had 10megs input impedance on all ranges. But that was only if you
had the money, or had some special reason for measuring voltages that
had high resistors in place, which was a much higher occurance in the
days of tubes.

Yes, if you are trying to measure voltages with really high value
resistors, 10s of megohms, in series, then your meter would start
affecting the readings. But even then, you're not trying to measure
exact voltages, you are merely trying to see what voltages land were.
A little drop, if it takes place, won't matter.

In 36 years of being a hobbyist, I've never needed anything more
than a meter with 10megs input impedance. Obviously I don't fiddle
around with things that have a lot of high value resistors where I
want to measure voltage, but you aren't at that stage either.

A higher impedance meter is for out of the ordinary need.

Michael

I am looking for an OP amp that I could use to make a voltage follower
to boost the input impedance of my DVOM up considerably. I am
primarly experimenting with DC and low frequence AC signals. I would
also like the op amp to be in a DIP package so I can plug it into my
solderless breadboard.

Any help would be greatly appreciated. Thanks

 

[John Fields]

On Tue, 19 Aug 2008 12:53:22 GMT, NoSpam@daqarta.com (Bob Masta)
wrote:

..
..
..

And the main virtue of an instrumentation amp
is low common mode rejection.

---
Low???


JF

 

[John Fields]

On Mon, 18 Aug 2008 11:55:28 -0700 (PDT), "jalbers@bsu.edu"
<jalbers@bsu.edu> wrote:

I am experimenting with various OP amp circuits based on the 741 . I
know that it is an old op amp but I have a bunch of them and I am not
trying to build anything important right now. Just trying to learn.
For example I have been experimenting with a peak detector circuit
using a single 741, diode, and capacitor. I am using a DVOM with
about 10Meg ohm input impedance to measure voltage drops at various
places around the circuit and seeing what happens. I have a feeling
that the impedance of the DVOM is putting more of an effect on the
circuit than what I would like. I am currencly using a Circuitmate
DM25L DVOM.

I am looking for an OP amp that I could use to make a voltage follower
to boost the input impedance of my DVOM up considerably. I am
primarly experimenting with DC and low frequence AC signals. I would
also like the op amp to be in a DIP package so I can plug it into my
solderless breadboard.

Any help would be greatly appreciated. Thanks

---
http://en.wikipedia.org/wiki/Instrumentation_amplifier

JF