How to deal with phase inversion?

[fryingpan]

In a pedal (a "soft" overdrive) I'm designing from scratch, I have four inversions total, two from JFET amplifiers and two from inverting opamps configured as tilting EQs. The design lacks an output stage. If I use a transistor as an amplifier, I'd get phase inversion. If I want to use a non-inverting opamp, I would need to include another single opamp (such as a TL071).

So, what would you do?

1) use a common base/gate transistor stage; the previous stage would be low impedance anyway (it's an inverting opamp), I don't need much gain (let's say 15dB) so I can probably get away with using, like, a 10K resistor on the collector. Disadvantage: I'd have essentially an unbuffered output that would be very sensitive to following impedances;
2) just add a non-inverting opamp. Disadvantage: it's a bit like using a pneumatic drill when you just need a small hammer;
3) use two cascaded amplifiers. Disadvantage: one extra transistor.

[GibsonGM]

A:  Anything you want.     

If you post your design, you'll get a few different opinions.     If the output impedance is 'low enough' (what that is is debatable), and the signal level is high enough...then you NEED not do anything at all.

If you want to make up gain (requiring a gain stage) or present a 'better', lower impedance to the following circuit(s), then a buffer may be all you need.  Could be a BJT/FET stage or opamp, your choice.  Of course, many variations of these abound, copy away    

Whether the pedal inverts or not is up to you. There is no harm in a pedal doing so and is quite common; it's only an issue if you're mixing pedals in parallel (easily overcome) - and any well-designed mixer will have a phase inverting switch. 

[fryingpan]

A:  Anything you want.     

If you post your design, you'll get a few different opinions.     If the output impedance is 'low enough' (what that is is debatable), and the signal level is high enough...then you NEED not do anything at all.

If you want to make up gain (requiring a gain stage) or present a 'better', lower impedance to the following circuit(s), then a buffer may be all you need.  Could be a BJT/FET stage or opamp, your choice.  Of course, many variations of these abound, copy away    

Whether the pedal inverts or not is up to you. There is no harm in a pedal doing so and is quite common; it's only an issue if you're mixing pedals in parallel (easily overcome) - and any well-designed mixer will have a phase inverting switch.

The pedal features the following:

- an initial JFET stage providing some moderate amount of clean gain (JFET selected with a Vgs around 2V, around 10dB gain?)
- an inverting opamp used as a tilting EQ (from flat to -15dB bass, +15dB treble)
- soft clipping achieved with series resistor + antiparallel diodes to ground
- JFET stage (low Vgs) - the combination of the soft clipping and the JFET's own clipping results in a very rounded, smooth, yet incremental transition to "hard" clipping
- Big Muff tone stage, with around 10dB insertion loss?
- de-emphasis circuit (like the pre-emphasis circuit, but with the taper inverted)

Technically the 10dB gain at the beginning would be nullified by the BM tone stack, the second JFET stage will provide some 15dB gain, so I shouldn't need any further gain at the end and I could get away with a buffer, but there may be some configurations (eg. low volume into the second JFET) where you might not have much volume boost at the end or maybe even a volume cut.

[ElectricDruid]

If the last stage is an op-amp doing tilt EQ, I don't see the need to follow it with another buffer. Just stick a volume control on the end of it and call it done. You'll find a hundred pedals done like this. *If* you had an op-amp left over, you could stick a buffer after the volume control, but otherwise I wouldn't bother.

[GibsonGM]

Yep ^.   If it needs boost, put a recovery stage in. If not, it's good. 

(Schematic is more useful than a description - the actual part values give more info)