Some ideas for a clean balanced line driver?

[jasperoosthoek]

'5534 needs external compensation for low gains (as when your POT1 is dialed to zero).

'5532 is really the same thing, will be happy on 15V, except the compensation is built-in (not enuff pins on the DIP).

Thanks, you just saved me 6 euros .

Do you really need 5 Meg input?

Technically it is not really a buffer as it just connects directly to the guitar signal to feed the line input. The guitar signal is just fed through the effect without being altered and is sent to the first effect in the chain. A bit like an oldschool wah with no true bypass.

What is R3 for?

Hmm, you are right. I'll remove it.

@Jasper - sorry, a bit OT - what have you found to be the best software for your setup?

I'm only using Reaper at the moment as it is cheap and works ok for recording. I have not worked with other software yet. I'm first going to get a few good recordings before I start mixing and maybe then I'll try other software.

Thanks guys!

[liquids]

What is R3 for?

It's for noise, of course!    

Hmm, you are right. I'll remove it.

Don't feel bad.  In many situations where you need a resistance that is referenced to a voltage, your arrangement makes sense [I'm thinking of geofex SRRP/Mu-amp articles of the top of my head, but similarly, it's a very different situation electronically].  
But for an op amp arrangement like this, you may well 'just' need a clean voltage reference fed to the non-inverting input' and nothing else.

On the other hand, I admit I don't understand the why/why not here vs there in circuits, in general, to any fullness.

I have an old book on op amps that starts from the very beginning of working with op-amps, and moves into working with them from baby steps. In that book, it starts one sub-section regarding use of op amps in 'inverting' confgurations by suggesting there be a resistance of a specific value placed between the unused, non-inverting op-amp input and it's voltage as reference, and that it can and should be calculated according to specs(?), gain of the stage, etc....(hold that thought)

Good, knowledgable designers and their designs do this sometimes (Harry Bissel's Muffy III comes to mind), but even then don't bother in other places in the same circuit...

...following that discussion in the book, and how to calculate the ideal resistance as such....the same op-amp book follows that by suggesting it's not necessary, and more or less, just save the resistor and tie it to the voltage.
 
And that's when I closed that book, that day.  

In general, it might be a little more about how the (general) question is asked.  Same context, from scratch: why remove R3?  Or, from scratch: why not put a resistor between the non-inverting input and the voltage divider?

But like PRR and the aforementioned book suggest, all else being equal, 'if the difference between the presence and absense of the component is a negligable difference in real-world application, why bother using the cheap component & making space for it?'

Or, you could figure out how to calculate what the best resistance (if any) for the design would be, or the best compromise, and come across as intentional and it seem well thought out...maybe. 

But I digress...this is no longer a long-winded digression with thought of just the 'Art' of electronics, this is as if the The Philosophy of electronics...

[amptramp]

R3 may protect the circuit when it is switched off.  Just a thought, in case this was copied from some other design.

If the power supply drops instantly (crowbarred), the non-inverting input is held to Vcc/2 which declines with a time constant of 0.11 seconds.  The 5532 is rated for inputs within the power rail voltages and differential input voltages of one diode drop.  Without R3, the op amp is outside of its maximum ratings when the power is shut off.  You can also put a diode across R2 that is reverse biased in operation but prevents the Vcc/2 junction from exceeding the power rail by more than a diode drop during power down.  I am not certain that operating the inputs beyond the power rails will do any damage, but limiting the current through the back-to-back diodes may be necessary and R3 does that.

Device specs here:

http://www.onsemi.com/pub_link/Collateral/NE5532-D.PDF

[Gus]

I would do the buffer different or even the whole circuit different

What input resistance do you want?
Gain wanted?
output drive wanted?  what are you going to plug it into?
Input signal level?
There are more things to think about.

First define what you want.

[jasperoosthoek]

Guilty, I put it there because I saw it in another circuit. I don't remember where. I hoped you guys would notice it and you did .

@Gus, so what I need is a device that connects to my guitar without loading it and sends a buffered signal through a transformer and a long cable (usually 30ft) to a line input. The line input has a switch to select between -10dB and +4dB. The gain of the device has to be adjustable so the line input receives a signal as large as possible without clipping. Your thoughts ?