Should a pedal be non-inverting overall ?

[Vivek]

How important is it that a pedal should be non-inverting overall ?

How many really had oscillations and feedback or strange behavior etc due to some pedals being inverting overall ?

Does this only affect pedals in parallel or does in also affect pedals in series ?

Any famous commercial pedals that are inverting  ?

[iainpunk]

How important is it that a pedal should be non-inverting overall ?

How many really had oscillations and feedback or strange behavior etc due to some pedals being inverting overall ?

Does this only affect pedals in parallel or does in also affect pedals in series ?

it only matters if you do parallel processing, but using a phase switch can negate or intentionally create the problems/sounds that come with out of phase pedals.

Any famous commercial pedals that are inverting  ?

most of the wah's on the market, LPB1, Range Master, Blues Breaker, tonebender mk2, some maestro fuzztone's. do you want me to go on?

cheers, Iain

[Mark Hammer]

It doesn't need to be non-inverting.  It's just more convenient in some contexts if it is, as Iain points out.

But now that the topic comes up, it's probably a good idea if people indicate whether a given circuit provides an inverting or non-inverting output when they post it.  And while it is a much less likely occurrence, if a circuit provides a buffered bypass, and the phase is different for the buffered bypass compared with the overall circuit, it's good to either avoid, or at least mention that.

Phase inversion can always be easily coped with.  But you have to know it's there.

[iainpunk]

some fuzzes and octave things really dick around with the phase and it can be hard to say whether its in or out of phase, but most things should really benefit from a phase declaration.
sometimes, a 180 flip can make an overdrive or distortion (and extremely rarely fuzz) sound slightly different. since guitar signals aren't anywhere near symmetrical.

cheers

[Digital Larry]

some fuzzes and octave things really dick around with the phase and it can be hard to say whether its in or out of phase, but most things should really benefit from a phase declaration.
sometimes, a 180 flip can make an overdrive or distortion (and extremely rarely fuzz) sound slightly different. since guitar signals aren't anywhere near symmetrical.

cheers

That's an interesting perspective... but to split hairs even further, the relevant phase flip would be prior to the fuzz, not after it.

[antonis]

Most of pedals (if not all..) can't be strictly classified as purely "inverting" or "non-inverting" due to several phase lags/leads caused by various capasitive/resistive combinations..

e.g would you tag an inverting op-amp stage followed by an all-pass filter (incorporating LPF) differenty from a non-inverting op-amp stage followed by an all-pass filter (incorporating HPF) at the same high/low frequency..??

[toneman]

Can you, or anyone, really tell the difference?

[iainpunk]

some fuzzes and octave things really dick around with the phase and it can be hard to say whether its in or out of phase, but most things should really benefit from a phase declaration.
sometimes, a 180 flip can make an overdrive or distortion (and extremely rarely fuzz) sound slightly different. since guitar signals aren't anywhere near symmetrical.

cheers

That's an interesting perspective... but to split hairs even further, the relevant phase flip would be prior to the fuzz, not after it.

ow yes, i just realized that i didn't write it right:
sometimes, a 180 flip pedal in front can make an overdrive or distortion (and extremely rarely fuzz) sound different. since guitar signals aren't anywhere near symmetrical.
sorry for the confusion!

Most of pedals (if not all..) can't be strictly classified as purely "inverting" or "non-inverting" due to several phase lags/leads caused by various capasitive/resistive combinations..

e.g would you tag an inverting op-amp stage followed by an all-pass filter (incorporating LPF) differenty from a non-inverting op-amp stage followed by an all-pass filter (incorporating HPF) at the same high/low frequency..??

i think its more important to just look at the fundamental and simplify, so yes, the LPF all pass doesn't invert the low tones, the one with a HPF does invert the fundamental's phase.

Can you, or anyone, really tell the difference?

in front of an asymmetric (mainly transistor) drive? yes! my humbucker guitar makes less (almost no) difference than my single coils for instance (stil not a huge change, but noticeable nonetheless). when it comes to parallel pedals, the difference is huge and out of phase really sounds weird and thin.

cheers

[ElectricDruid]

Can you, or anyone, really tell the difference?

Not alone, you can't, but in combination with other things it can be very obvious. The "parallel paths" scenario will often make an inversion very obvious, since the fundamental of the waveform can almost completely disappear.

I'd say that non-inverting is a good goal to aim at, and to be regarded as "best practice", but I wouldn't go out of my way to re-design something just to flip the signal if the design finished up inverting.

The Druid DigiDelay pedal is inverting, for example, since it uses a non-inverting buffer at the front, and an inverting mixer for the dry and wet signals at the end. So the dry signal finishes up inverted. For the delays, all bets are off, since the phase would depend on the exact delay and the frequency, so it can be ignored.
The Druid FilterFX is another interesting case. Since it's a State Variable Filter, what phase the output is depends on whether it is set to LP, BP or HP mode. But I wasn't going to add extra op-amps just to flip a couple of outputs before the mode switch, especially since filters muck with the phase anyway (as Antonis mentioned already with Allpass filters).

[Vivek]

This is the sentence that got me thinking about phase :


The final op-amp 4a is a simple unity-gain inverting stage. To be honest, I'm not sure what this is doing here. Perhaps Boss were concerned that the pedal should be non-inverting overall (is it? I haven't checked) or perhaps they had one op-amp left over. Suffice to say, it doesn't add anything, just flips the signal the other way up.

https://electricdruid.net/boss-mt-2-metal-zone-pedal-analysis/

[stallik]

I'm with Tom on this one. Parallel audio paths will highlight phase differences, sometimes massively. But it's not just a case of making sure that every pedal has the same phase between input and output. Even if all pedals have the same phase relationship, there are times where combinations of effects sound better and bigger if they are out of phase with the dry Chanel.
A phase switch on one Chanel is a damned useful thing to have...

[iainpunk]

the flashiest use of a phase inverter or attenuverter, is when you run multiple amps, putting one out of phase gives it a huge stereo spread. this is really cool live on stage.

cheers

[stallik]

It's damned impressive in my bedroom too!

[iainpunk]

It's damned impressive in my bedroom too!

i think everyone should try that with 2x 50W tube on a stage, its just majestic!
cheers

[ElectricDruid]

This is the sentence that got me thinking about phase :

The final op-amp 4a is a simple unity-gain inverting stage. To be honest, I'm not sure what this is doing here. Perhaps Boss were concerned that the pedal should be non-inverting overall (is it? I haven't checked) or perhaps they had one op-amp left over. Suffice to say, it doesn't add anything, just flips the signal the other way up.

https://electricdruid.net/boss-mt-2-metal-zone-pedal-analysis/

Hohoho! "Hoist by your own petard" is the expression in English!

Still, I stand by the remark. the stage doesn't do anything except invert the signal, and I'm still not sure whether the MT-2 is inverting. I was sure I remembered someone mentioning it in the comments on that page, and suggesting that without it the pedal would invert, but I can't find it any longer.

I'm with Tom on this one. Parallel audio paths will highlight phase differences, sometimes massively. But it's not just a case of making sure that every pedal has the same phase between input and output. Even if all pedals have the same phase relationship, there are times where combinations of effects sound better and bigger if they are out of phase with the dry Chanel.
A phase switch on one Chanel is a damned useful thing to have...

Totally agree. And if I was building a 2:1 mixer circuit to provide parallel effects, I'd certainly add a phase-flipper switch on at least one of the channels (one should be enough!).

[iainpunk]

...And if I was building a 2:1 mixer circuit to provide parallel effects, I'd certainly add a phase-flipper switch on at least one of the channels (one should be enough!).

my local shop has the pots cheaper than switches, so i'd recommend attenuverter over a phase switch, especially when you are using opamp buffers already.


cheers, Iain

[ElectricDruid]

...And if I was building a 2:1 mixer circuit to provide parallel effects, I'd certainly add a phase-flipper switch on at least one of the channels (one should be enough!).

my local shop has the pots cheaper than switches, so i'd recommend attenuverter over a phase switch, especially when you are using opamp buffers already.


cheers, Iain

Yes, nice idea.

[iainpunk]

i think attenuverters should be utilized more often, especially when mixing.
especially if you are mixing inside a pedal, clean and distortion for instance, you could go from hard and soft clipper to controfuzz sounds. (i used it in the mixing stage of my controfuzz interpretation)
but having it as a pedal as-is is also a cool toy/utility, some overdrives and distortions sound different if the clean input is flipped 180 degrees (since guitar signals aren't symmetrical.) or when running dual amps, the out of phase sound is a cool super wide stereo effect.

cheers, Iain

[ElectricDruid]

i think attenuverters should be utilized more often

I agree. Although I've had trouble actually pulling it off.

I tried an attenuverter for the feedback pot in the prototype of the Flangelicious flanger pedal. Unfortunately the behaviour of the pedal with large amounts of negative versus positive feedback meant it was difficult to get a decent response out of the knob for both settings. Attempts to rectify that by allowing separate trimming for the two different extremes just led to the zero point not being in the centre! It's a shame, because it would have added an extra feature without adding any extra knobs (and how often does *that* happen!). Maybe one day I'll go back to it and see if I can't do it better.

[antonis]

Flangelicious flanger pedal.

Which pedal, IMHO, should be renamed Frangelicious..

P.S.
Never managed to get pure "steps" or "staircase" waveform, Tom..
(but cheers, anyway..)