Inverting Opamp Stage Question

[Suicufnoc]

I've been trying to avoid inverting op amp stages but I'm using an active Bax this overdrive I'm working on so I need to get my signal flipped back to normal, and I'd prefer not to add a whole new stage to do it.  So I've decided to try switching my clipping stage to an inverting gain stage.

I know the inverting stage has lower input impedance, but it's being driven by another op amp, so I'm not real concerned about that.  I'm thinking that at lower gain levels, the frequency response of my RC network changes a little, which doesn't concern me too much.  Are there any other differences I'm missing?  Is this even right?  Thanks

[earthtonesaudio]

Without the diodes this would be perfectly fine, the gain of the inverting configuration will be -[(gain of non-inverting configuration)-1].  With the diodes, the two versions will sound completely different.

[Suicufnoc]

I take it the clipping will be harder in the inverting stage?  Actually harder even than diode to ground clipping, I'm thinking.  I guess that means I'll have to add another stage.  I'm thinking of:
a) Adding a high impedance inverting buffer before my first stage.  (Can I do this with one tranny?)
b) Converting my first stage to inverting, then add a non-inverting buffer before it to get the impedance back up.  (I don't know if I can do this and keep my cap switching around the stage working the same.)
c) Not worrying about the output being inverted.  I'm thinking this makes it more prone to popping when engaging/disengaging the effect?

[slacker]

Yeah the inverting stage with diodes gives hard clipping, sounds totally different to non inverting. Personally I'd go with option C and not worry about it, inverting the signal shouldn't make it any more likely to pop. With all the RC filters and the Baxandall, the phase of different frequencies is going to be shifted any way so what ever you do it's not all going to be "in phase" compared to the input anyway.
You could use a passive Baxandall instead and use the a non inverting stage after it to recover lost volume.

Looks interesting.

[Suicufnoc]

Good point there, wasn't thinking of the phase shifts.  I considered a passive Bax stack, but supposedly there's less interaction between the two controls in an active stack.  Also I'm thinking less noise maybe?
Well cool then.  No need to tweak my maddening vero layout.  (5 onboard pots and strips all running the short way means lots of jumpers...)
Thanks for the help.

I'll have clips and a vero layout after it's verified.  Sadly I won't get a chance to build it for a week...

[earthtonesaudio]

I take it the clipping will be harder in the inverting stage?  Actually harder even than diode to ground clipping, I'm thinking. 

Actually, the inverting clipper IS a diodes-to-ground clipper.  Virtual ground, but still.

[amptramp]

You will notice a difference.  The non-inverting clipper is like the TS in that even when it is driven hard into clipping, there is a gain of +1 for the undistorted input signal, which is added to the clipping level.  If you switch to the inverting clipper, you lose this and you just get a signal that flatlines at the positive and negative clipping levels.  A bit of resistance in series with the clipping diodes may fix that.

[WGTP]

The op amp Muff Fuzz uses an inverter stage for distortion.  Here are some modded ones.  I'm not sure it sounds the same as the typical diode to ground distortions, since the diodes in the loop MAY limit the amount of distortion the op amp contributes???

http://www.aronnelson.com/gallery/main.php/v/WGTP/AlteredMuff.jpg.html?g2_imageViewsIndex=1

Just saw Rust Driver post - http://www.diystompboxes.com/smfforum/index.php?topic=92234.0

[earthtonesaudio]

The op amp Muff Fuzz uses an inverter stage for distortion.  Here are some modded ones.  I'm not sure it sounds the same as the typical diode to ground distortions, since the diodes in the loop MAY limit the amount of distortion the op amp contributes???

Ah, good point!  Especially since a lot of diodes-to-ground clippers also drive the op-amp itself into clipping.

[WGTP]

Also, there is a resistor in parallel with the clipping diodes, again I'm not sure how much that effects the clipping.  I tend to think of inverting op amp distortions as having a warmer fatter sound, perhaps because of the lack of op amp clipping??? 

[earthtonesaudio]

Parallel resistor shouldn't affect it much, since the op-amp output is basically a voltage source.  I would imagine the different sound could be attributed mostly to the op-amp clipping or not.

With ideal parts at least, they act identical:

simulation