Questions for Radio Shack LM741

[econpatric]

Hey all,
I will preface all this by telling that I am a newborn in the DIY world.

I recently bought the LM741 chip and am trying to hook it straight up without the caps and resistors just to get a quick fix. I did this with the LM386 chip with no problems, but I am wondering if this is possible to do with the 741? So far I have had no luck, and am beginning to think I may have a bad chip. If not what is it that has to change and why in order to make the chip function?

I also have done a fair amount of research, but have had a hard time understanding how these IC's seem to have differing + and - inputs. The Radio Shack packaging shows the + on pin 3 and - on pin 2 and the schematics that I have show this to be opposite (Distortion+). I feel foolish asking as I'm sure, these are obvious questions.

Thanks 

[Mark Hammer]

Don't let the same triangle shape on a schematic fool you.  They are different beasts, although admittedly a badger and a lion will dine off the same carcass on occasion.

The gain of the LM741, or indeed any op-amp, is set in a different manner than the LM386.  I'd say you're gonna need a little more reading, both here and lesewhere, before firing up the soldering iron.

[familyortiz]

Yes, they are different in pinout and function.:
1) The LM386 has V+ on pin 6. The LM741 has it on pin 7.
2) The output pin on the LM386 is on pin 5 as opposed to pin 6 on the LM741.
3) Functionally, the LM386 is an audio amp with preset gain without any external components. The LM741 is an opamp where gain must be defined with external components.

[Mark Hammer]

The gain of a 386 is set internally by a 1.35k resistor, and external components increase the gain by providing another parallel path.  In the case of op-amps, the gain is also set but is ridiculously high, and one uses external components to reduce the gain down to what is appropriate for the circuit in question.  Different strategy entirely.

[econpatric]

So, I think I understand... The LM741 needs external components to properly function.

What about the labeling of the 741, why does the Distortion+ invert the position of pins 2 and 3 compared to the Radio Shack packaging? Pin 3 is still positive, and pin 2 negative but they are flipped on the schematic.

Also, I would be interested to know where a discussion of good merit, and ease of understanding could be found either here, or anywhere on the net for the ideas and workings of the OP AMP. I don't mind putting in a little leg work. So far I haven't  found anything that was very easy to understand.

[Mark Hammer]

Go here - http://hammer.ampage.org/?cmd=lt&xid=&fid=&ex=&pg=12 - and look at Issue 1 of DEVICE.  The look at Issue 2 through 12.  very helpful and still a useful source of insight even though its over 30 years old. 

Then, I recommend bopping over to Jack Orman's AMZ site: www.muzique.com and looking through the lab-notes where a number of other things essential to pedal building are explained at a level suitable for beginners.

It'll take a little while, but the requisite learning for such matters is now a mere 1/10 or 1/20th of what it was when us old farts were starting out.  You latecomers are lucky.

[familyortiz]

econ,
   The external components thing is secondary... these 2 devices are pinned out differently. Here are the datasheets:
http://www.national.com/ds/LM/LM741.pdf
http://www.national.com/ds/LM/LM386.pdf

The + and - inputs to the amp are the same for each, so the thing you're looking at has a typo if they're switched.
In any case, National Semiconductor has their Linear Applications Databook which covers most basic opamp configurations in an easy to understand manner, complete with relevent equations for gain, frequency response, etc. They might have some of this out there on the web.

[Electron Tornado]

This should also be helpful reading:

http://focus.ti.com/lit/an/slod006b/slod006b.pdf

[stringsthings]

Hey all,
I will preface all this by telling that I am a newborn in the DIY world.

I recently bought the LM741 chip and am trying to hook it straight up without the caps and resistors just to get a quick fix. I did this with the LM386 chip with no problems, but I am wondering if this is possible to do with the 741? So far I have had no luck, and am beginning to think I may have a bad chip. If not what is it that has to change and why in order to make the chip function?

I also have done a fair amount of research, but have had a hard time understanding how these IC's seem to have differing + and - inputs. The Radio Shack packaging shows the + on pin 3 and - on pin 2 and the schematics that I have show this to be opposite (Distortion+). I feel foolish asking as I'm sure, these are obvious questions.

Thanks  

welcome to the world of DIY  ... and the 741 is an excellent chip to start your DIY experience ... ( not necessarily because of guitar-centric sound quality, but for its proven design, availability and low cost ... and it's pretty close to an industry standard in the universe of oppy amps )

what are you currently trying to do with DIY?  that answer will give us some specifics that interested cyber-jockeys can chime in on ... as stated in previous posts, while the 386 and the 741 may look similar on paper, they are indeed two different beasts ... the 386 is a low voltage power amp, while the 741 is a general purpose operational amp ... so they both have the ability to take a small signal and make it larger .... how they go about performing that task is different ...

don't feel embarassed to ask questions ... as someone wiser than me once said, "there is no such thing as a stupid question, just stupid answers" .... and once again, welcome to the world of DIY  

[econpatric]

Thanks for the websites referring to Op Amp's. I have been on many of them before coming here and I'm sure they good for a veteran DIYer, but I am thoroughly confused with much of the lingo. Been to muzique.com and didn't see any discussion specifically relating to Op Amps?

Although a lot of the confusion has been cleared up with the differences on the 386 and 741 (thank you!! ), I still feel that my primary question remains unanswered... After reading the posts I realized that my LM741 needed to be nestled in between many components in order for it to work properly, so I grabbed the schematic of the MXR distortion+, plugged the necessary components into my breadboard and had a functioning circuit in short order...

The question that remains unanswered is: if I want a quick fix with the LM741 what are the bare essentials (caps and resistors) regarding the input and output section required to make the op amp work and (if not too much to ask ) why? I can get the chip working, but how is it working?

[kurtlives]

Bare essentials,
A input and output caps, feedback resistor and source resistor. This is the very minimum, wont work great and could be added on a lot.

All these components do is set a fixed gain instead of some huge gain (open loop gain) and block DC on your input and output signals.

[familyortiz]

econ,
If you want to try the LM741, here is what you have to do given what I previously wrote on the pinout differences:
1) pin 6 on the existing LM386 design must be sent to LM741 pin 7. This is the V+ supply input. (not the noninverting + input to the amp!)
2) Pin 5 on the existing LM386 design must be sent to LM741 pin 6. This is the amp output signal.

The next step is trickier and has to do with external components and what the existing design looks like. Can you post a link to the design?