Best Dual Op Amp for a Clean Boost?

[mistapitts]

I've been messing around with a design for a clean boost/preamp pedal with an active Baxandall tone stack. Currently I'm planning on using an NJM4558D, but some research has suggested that while that chip is great for an overdrive, it may color the sound too much for a clean boost.

Any suggestions for an alternative? Leaning towards the TI OPA2134.

[Brisance]

it may color the sound too much for a clean boost.

Really?, I mean we are talking about guitar effects here, I am certain, even if it does, you will not hear the difference.

Speaking of which, what's wrong with the good old TL072?

[mistapitts]

what's wrong with the good old TL072?

How does it compare to the 4558? Or is the difference really that negligible?

[GGBB]

In a clean guitar pre-amp implementation, they will all sound basically the same. Some might have a little less background noise than others, but this is also likely to be indistinguishable in a low-gain guitar pedal application. The lowly TL072 is an excellent choice as its JFET input has very high input impedance. I've compared the 4558, TL072, OPA2134 and others in a compressor pedal and ended up with the TL072 because it sound as quiet as or quieter than any of the others (compressors can be noisy) and was cheap. There were some extremely minor tonal differences (subtleties really), but that is more likely to be due to input and output impedance differences of the op-amps and the interaction with the circuit around it. Design and build your circuit with a socket for the op-amp, then try out a bunch of your favorites.

[Mark Hammer]

1) The cleanliness of the boost will depend fundamentally on how much headroom the op-amp has.  In turn, that will depend on the power supply.  I'm confident that an OPA2134 can be made to sound like crap if the supply voltage is too low, and that even a 741 can sound better and cleaner if provided with a higher supply voltage.

2) "Cleanliness" depends on what comes after the boost.  Most people will tend to use "clean" boosts to overdrive their amp, rather than to simply shift levels with no change in tone.  Once you're pushing your amp/speakers into breakup, why does the cleanliness of the boost matter?

3) Cleanliness is a lot easier with limited bandwidth than with wide bandwidth.   Remember that the "dirt" is harmonics, which is higher frequency content that a guitar amp will tend to ignore/roll off.  Differences in op-amps that matter for wide bandwidth content (symphony orchestras), may simply be moot when it comes to processing guitar or bass.  An OP2134 may be MUCH better than a TL072 or 4558 in a CD preamp/control-amp, but may not be ANY better in a pedal or guitar amp front end.

[grrrunge]

If you need as much clean headroom as possible, try looking into some rail to rail op amps, that fit your supply voltage.
Try looking into the AD803x series from Analog Devices. They're a bit expensive, but the specs look good