benefits of using a single vs. dual op amp with diode clipping section

[mordechai]

I plan on building an overdrive circuit that will include a diode clipping section (asymetrical) in the feedback loop of the op amp.  I am wondering what the benefit would be to using a single op-amp as opposed to a dual op-amp, or vice versa.  I am more interested in a quiet component when push comes to shove, and also wonder whether the variants in the clipping section (using a 1 against 2 diode setup as opposed to a 2 against 3 setup, or perhaps 1 against 1 with a resistor) matter in choosing the right op-amp for the project.

[R.G.]

I plan on building an overdrive circuit that will include a diode clipping section (asymetrical) in the feedback loop of the op amp.  I am wondering what the benefit would be to using a single op-amp as opposed to a dual op-amp, or vice versa.  I am more interested in a quiet component when push comes to shove, and also wonder whether the variants in the clipping section (using a 1 against 2 diode setup as opposed to a 2 against 3 setup, or perhaps 1 against 1 with a resistor) matter in choosing the right op-amp for the project.

Single vs Dual opamp has no bearing other than making layout easier or harder.

Variants in the diode arrangement have no bearing on noise.

[Mark Hammer]

If you are building it on perfboard, having the second op-amp section on a single chip will provide you the option of adding some sort of EQ or gain recovery stage, should you choose to do so.  In terms of performance from the single section you do use, there should not be any difference between that and a comparable single op-amp of the same type.

[mordechai]

Hi Mark and RG, thanks for the clarification.

I like the idea of the dual op-amp giving me a chance to recover some gain to compensate what is lost from the clipping section.  Is it possible to do this with FETs running out of the second op-amp stage? I am thinking about trying to get the clipping in the op-amp to drive JFETs into overdrive, since I've been really impressed with the MOSFETs' and JFETs' ability to provide a natural, organic type of overdrive on their own (such as with the Pepperdrive).  What do you suggest?

[merlinb]

Dual opamps also tend to be cheaper than singles, because they are more widely used in the industry. Dual opamps are also always unity gain stable, whereas some single opamps are not, and require external stability components, which can really trip you up if you're not savvy with the part numbers!.

[mordechai]

Is there a particular benefit to using the JRC4558 op amp from the TS 808 series?  Is that responsible at all for the midrange "bump", or is the bump a matter of the cap/resistor outside of the op amp?  I'd like to avoid the bump or, perhaps, have it less pronounced.

[R.G.]

Is there a particular benefit to using the JRC4558 op amp from the TS 808 series? 

Basically, little if any. It is quite difficult to hear differences in opamps in the tube screamer. It is arguable that most people can't. But it makes a great "vintage is better" advertising blurb.

Is that responsible at all for the midrange "bump", or is the bump a matter of the cap/resistor outside of the op amp? 

Geofex.com, "Technology of the Tube Screamer".

No, it's not the opamp. Most modern opamps are quite difficult to hear differences in.

To the naysayers: "quite difficult" is different from "impossible" but includes it.

I'd like to avoid the bump or, perhaps, have it less pronounced.

That's an overall circuit design issue, not whether a particular opamp is used or not.