Non-conventional Opamps

[vdm]

Hi!
It's been a good while since I've posted around here, but it's working very well to help me procastinate from studying for my end of year university exams 
I've been looking at and reading about a bunch of different opamp based distortions, and a few things have been on my mind.
Firstly is there any sound difference in putting a 1n4148 diode across the + and - inputs of the opamp? I couldnt see any reference in datasheets to it, so it didn't stike me as a protective measure, but please let me know if that's all it is.
Reading through the datasheets for the TL071 I was intrigued by the null offset pins and wanted to know if and how anybody has used them. I'd love to experiment but I just dont know where to start.
Thanks for any help guys,
Trent

[Eric H]

Hi!

Firstly is there any sound difference in putting a 1n4148 diode across the + and - inputs of the opamp? I couldnt see any reference in datasheets to it, so it didn't stike me as a protective measure, but please let me know if that's all it is.

Take a look at this:
http://www.geofex.com/circuits/what_are_all_those_parts_for.htm

-Eric

[toneman]

welcome back...
why not try your suggestions on a sim??
that's "simulator". I believe MultiSim makes a student version.
I've discovered LTCSpice recently...it's awesome...& it's free.
Offsets are for puting a DC output where U want voltage-wise.
There are lots!! of info on offsets at the AnalogDevices & National pages.
Remember, OpAmp stands for "OperationalAmplifier".
Originally opamps were made for performing analog "operations" as addition, subtraction, multipling, etc. 
Offsets were important in setting up for mathamatical accuracy.
B4 digital, all there was was analog.
To calculate a trajectorys in real time was one instance where opamps  were first used.
stayinganalog
tone

[vdm]

Hey great!
I knew i'd seen that diode somewhere before - just didnt think to look at GEO
I'll certainly be having a look at those datasheets and learning more about offsets after my exams, but do you know any pedals that have used it?
continuing on the analog journey
Trent

[R.G.]

Firstly is there any sound difference in putting a 1n4148 diode across the + and - inputs of the opamp? I couldnt see any reference in datasheets to it, so it didn't stike me as a protective measure, but please let me know if that's all it is.

That's all it is. In any kind of normal amplifier operation, the + and - inputs are only the input offset voltage apart, a matter of a few millivolts with most opamps. The diodes keep you from destroying or damaging the input transistors by pulling the inputs apart more than a diode drop. There's no difference to the sound.

Reading through the datasheets for the TL071 I was intrigued by the null offset pins and wanted to know if and how anybody has used them. I'd love to experiment but I just dont know where to start.

The null offset pins are just additional inputs that have non-standard characteristics. Look at the internal schematic of the opamp in in question, and you can usually tell something about what they do.

[Paul Perry (Frostwave)]

Look at the internal schematic of the opamp in in question, and you can usually tell something about what they do.

Yeah, some gold waiting to be discovered (or rediscovered..) there

[jrc4558]

Hey toneman!!! I am really curious to try the software you're talking about. Care to post a link? Thanks!