Replacing LM 741 wiht a 4558 ?

[niggez]

Hello,

After 2 years abstinence i want to get started with building stompboxes again. My first project ist the MXR Distortion + from tonepad. My problem: I dont have any 741 IC's, but a lot of 4558's. Isnt the 4558 a dual version of the 741? So could I somehow use a 4558 to replace the 741? If so, how?

[frequencycentral]

Yeah, but just use half the 4558, check the pinout on the data sheet, as it''s pinout is not a drop in replacement for the 741. You'll have to modify whichever layout you plan to use, or come up with your own layout. Or, make a Tube Screamer, that uses a 4558.

[niggez]

Ok, thanks. Yep i found the datasheets. Since im only breadboarding it to see how it sounds first, the different pins wont be a problem.

[niggez]

Hello again.

So i tried breadboarding the thing. According to the IC's diagrams, I only have to change the output from pin 6 (With LM 741) to pin 1, and the V+ from pin 7 to pin 8. I hope I'm not makin ga mistake here. Here are the diagrams:

http://pdf1.alldatasheet.com/datasheet-pdf/view/7457/NJRC/JRC4559.html

http://www.datasheetcatalog.org/datasheets/90/53981_DS.pdf

But somehow, I'm losing the signal in the IC. It's still there when I probe at pin 3, but nothing getting out at pin 1. So I assume I still have overlooked something.. I left pins 5, 6, 7 unconnected!

[theehman]

 I believe the 4558 isn't close enough to the 741.  The 4558 is an improved version that doesn't use as many external components.  I'd wait until I got a 741.  They're cheap and easy to find. 

[niggez]

On the tonepad reviews, theres a guy saying he used a 4558. And I've found some other people reporting about using one side of a 4558 instead. I dont mind the thing not being close to the original, as long as i get it to work. And I mean looking at the diagrams of the opamps, why should it not work?

I found a schematic using the 4558, i guess i should get it to work the way i looked up my pins. The problem must be hidden somewhere in my breadboard

http://www.beavisaudio.com/bboard/projects/bbp_MXRDistortionPlus_Rev_1_1.pdf

So I'm still troubleshooting. IC VOltages are:

pin1: 9 V
pin2: 8.17 V
pin3: 0.22 V

I also tried it with the other part of the dual opamp, pins 5, 6, 7. In this case, leaving pins 1, 2, 3 unattached. But still, I lose the signal at the IC.

Audioprobing gives me signal up to the point where it enters the 4558 at pin 3, then nothing comes out at pin 1. Any suggestions?

[sean k]

Well your doing something wrong because all those voltages should be about 4.5.
Pin 3 should definitely be at 4.5 because it's on the bias network of all those 1M's and so because 3 is at 4.5 then pin 1 will be at 4.5 and so put that same DC voltage at pin 2. Check your bias network and make sure you have 4.5 at the junction of R1 and R2. If it's there...it'll be everywhere.

[niggez]

Thanks for that hint! The SOlution was quite simple.

I had used different kinds of resistors, and forgotten, that the blue colored ones use a different coding system - there is one extra bar before the stripe denoting the multiplier. I quickly found my error once you pointed me to the bias section, and i had quintuple checked my breadboarding After replacing the very small value resistor by the prober 1M -> Voila, MXR Distortion +

THank you very much again.

[drk]

you could use the other half of the op-amp for something else, for example a buffer or for a active tone control. Kinda of a waste to let it be there unused 

[frequencycentral]

My current favourite use for a single opamp stage is the filter part of the Dr Q/Nurse Quacky. No need to drive it with an envelope follower, just use it as a 'stuck wah' type  tone control by using a pot to ground.