4 op-amps on one chip

Hello Blair,

Check the datasheet for the allowed input common-mode range. Often you must stay a Volt or two away from the most negative supply (in your case that seems to be ground). Else weird things can happen.

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Regards, Joerg

http://www.analogconsultants.com

Do you expect to get a negative output when you are only giving it a positive supply voltage?

The output has to come from the supply and so will be limited to about

0-30V for a typical single supply opamp with a 32V supply.

Usually you would supply the amplifier with a positive and a negative supply and connect the non-inverting input to ground. In this case you may be limited to +- 16V.

kevin

Thanks Kevin,

Now I can finally move on, and won't lose any sleep!

Joerg a écrit :

Really? Even the 324 (which we can suspect it is) would do that :-)

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Thanks,
Fred.

Hello Fred,

I know. It can even go a bit below and that (and its price tag, of course) is the reason I use it all the time in designs. But Blair did not state which amp he uses and he needs to check whether his opamp can also do that. There are some that can't. I don't remember the 709 and

741 but many hobbyists still use them and AFAIR they CM range was rather limited.

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Regards, Joerg

http://www.analogconsultants.com

Sheeesh! By ANY modern standards the 709 and 741 are CRAP!

And 324's need to be treated with caution... many _brand_ names have extraordinary cross-over distortion.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

The 709 wasn't that bad. Of course, in those days I did almost everything with discretes as opamps were quite expensive or used too much quiescent current. However, I see lots of hobbyists use the 741 because that's what they found in pa's shoebox on the garage shelf. For mundane jobs those amps are ok. My favorite for hot stuff was the 733 where you got a rocket at Walmart pricing.

I never use them for anything fancy but they are a real bargain for DC work. Around two cents per amp there ain't much else in that class. AFAIR it was the first chip I came across in my career where I couldn't beat its cost with a discrete solution.

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Regards, Joerg

http://www.analogconsultants.com

I spec'd one of them once in a bog-simple feedback buffer to go to a uC's ADC inputs. One with a voltage divider for volts, and one with a shunt for amps. The input range to zero with a single supply was the primary reason for my choice there.

For some reason, though, when I did my audio project, I used a bank of TL084s - probably because those were the ones in the company's bin. ;-) (I had a neat gig at the time, where the outfit I was working for had bought a whole stockroom from a former company at liquidation prices, and the rules were, "use whatever you need in the lab, but don't take any home wink, wink, nudge, nudge." I was like a kid in a f---ing candy store!)

Cheers! Rich

Weird things like posts to s.e.d?

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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I love guns. Its bullets that I can\'t stand.

Joerg a écrit :

You know, I know you know :-)

But Blair almost stated he was using it single supplied, and I just meant that obtaining a negative output swing from this configuration would be out of reach of any op amp, whatever input CM it accepts.

I should have been less cryptic.

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Thanks,
Fred.