I have a DIY made guitar amp in which there is a TL071 preamp section. I read various opinions about how upgrading op amp improves that sound and how it doesn't do anything really... I'm quite confused - would upgrading TL071 to OPA134 make a distinctive difference in sound and quality? And if not is there any other advantages in upgrading? And what other op amps would you recommend that would be a 'direct' replacement for TL071 instead of OPA134 (I don't plan to spend big so it should be on the cheap (up to 3-4$). Another thing which I could not find myself is whether a 'better' op amp improve the output level? Bigger output really wouldn't hurt for my little amp - there would be lots of more headroom for various instruments :) I think I should mention that two inputs goes to the preamp (connected by two resistors).
Chances are low that you will notice any affect by changing the opamp, assuming the two are even compatible in the first place. You didn't provide links to datasheets, so I haven't checked.
A TL07x opamp, when used properly, can make a nice audio amplifier. It can also make a mess, as can any opamp, when used improperly.
Gain is a function of the circuit around the opamp, and output voltage swing largely a function of the circuit. The TL07x series do have rather high power rail headroom requirements, but presumably that was taken into account in the design of the circuit. The opamp, unless it's really bad, should have little effect on "sound quality", whatever that actually is anyway.
In general, just replacing a part in a competently designed circuit with something that supposedly has higher specs is not a good idea. You don't know what the design considerations were, and don't know exactly how the part is used.
If you don't understand a circuit, don't mess with it.
Hah, the OPA134 is one of my fav. Fet opamps. It has some "better" spec's than the TL071. Whether these "better" specs will make a difference in your circuit will depend on the circuit. It's also entirely possible that the higher BW (for instance) will make your circuit oscillate.. (which would be worse :^)
1.) less noise
2.) higher unity gain BW and slew rate.
3.) more current (maybe I could not find the max current spec on the TL071.)
Well as silly as it may seem. I tried replacing, just for the sake of experimentation. And, well.. It affected the sound - it was not much but it didn't seem so harsh and sounded more balanced. Perhaps it depends on the circuit.
One thing that it did solve is helped a lot with distortion (much less when driven with a hot signal) and impedance mismatch seems to work better with this op-amp.
Is it worth it? Probably not, unless you are designing high-end amplifier or need those values, balance and reliability.