TL071 .vs. LM308

[Da PlaN-R]

I'm trying to build this thing (guitar distortion pedal)

http://generalguitargadgets.com/diagrams/rodentsc.gif
http://generalguitargadgets.com/diagrams/rodentpl.gif

And I had basically all of the parts except for the opamp and have allready soldered most of them on (making this on perfboard) minus the resistors (didn't get everything in one batch and didnt huryy with them when I realised it'd be a pain to get the opamp)

I managed to get the LM308s but they're round ones (LM308H), not the regular square type that you'd use a socket for (which I allready soldered on). But I also got a couple of TL071s which apparently also work in the circuit (apparently they sound a bit more "modern"...) and I'm making another one so I can still use the LM308s in it....

Basically I just need what are the main differences between the pin outs because I have no idea what any of the pins besides the regular input+/-, output and v+/v- are for are for.


TL071 spec sheet
http://focus.ti.com/lit/ds/symlink/tl071.pdf

LM308 spec sheet
http://www.national.com/ds/LM/LM208.pdf

 

[Mohonri]

NC = Not connected
Offset = Comp (compensation) Used for adjusting the comparison between the two inputs. If the two inputs +/- have the same bias, you can just leave the offset pins unconnected. However, I would strongly encourage you to attach a small capacitor between each offset and ground. I've had a few weird things happen with ICs when pins aren't connected either to ground or to a smoothing capacitor.

Comp1 ----||-----GND
Comp2 ----||-----GND

 

[xonik]

OFFSET1/2: These are pins which let you eliminate or "null" the offset voltage present in most op-amps. As op-amps are differential amplifiers, input offset voltage must be controlled to avoid an offset output voltage. In case you didn't know, an offset voltage is a non-zero output voltage when the input voltage is zero.

Anyways, the OFFSET1/2 pins are connected together using a potentiometer. The center pin of the potentiometer goes to the negative supply voltage. Check the op-amp documentation for the potentiometer resistance value, otherwise give 10k a shot.

COMP/ COMP 2: These pins are connected together using an appropriate capacitor to allow for external compensation. The LM208 datasheet gives a good description of why and how to use these pins.