How does a pedal reverse phase?

[lowvolt]

I have a Telecaster that I modded that has separate output jacks for each of the 2 pickups (one volume control per pickup - no tone controls - this axe is for testing ideas and reseach).  I typically plug each pickup into two identical mic preamps to provide a good input impedance for them, and to serve as signal massaging tools.   The two signals are mixed together after the mic pres (and any other per-pickup-processing) with a small reliable mixer, then out to amp.  I've discovered that some pretty useful sounds can be had by processing each pickup differently, then mixing those two processed signals before amplifying them.  (*Yes* I have thought of separately amplifying each pickup, tried it --- ~meh~ --- but some folks might find that useful to do).  This rig also is fun to use for recording, placing each pickup chain on a separate track and doing *whatever* with each pickup track.  Anyhow .....

The two mic pres are identical and each one has a phase inversion switch (like most microphone preamps do), and of course I normally run them both in the same phase or I get that "out of phase" pickup tone (thin, loss of bass).  Fine, whatever -- ok on to my issue.

So, I this time, I ran the BRIDGE PICKUP ONLY straight in to a GGG Orange Sqeazer comp, then a jfet booster (I think it's the GGG Alembic Stratoblaster) ... then on to the mic preamp.  The neck pickup went directly to it's normal mic preamp, then both feeds went to the mixer as always.  When I engaged the booster, instantly I heard that familiar "out of phase" pickup sound.  So I hit the phase inversion button on the bridge's mic pre and instantly I got the nice full sound I usually get (so at this point the neck's mic pre is set on "+" and the bridge's mic pre is set on "-").  If I roll off the neck pickup's volume at the guitar, the bridge's sound fills right out no matter which polarity the mic pre is set on.  The moment I use both pickups, with that booster pedal engaged, I must invert the bridge pickup's phase at the mic preamp using the little button.  If I bypass (true) the booster and just run the comp, all is well in the kingdom, no phase issues.  However when I engage the booster, it somehow inverts the bridge pickup's phase and I have to push the little button on the mic pre to "re-flip" that pickup's phase to make the blended pickups sound fuller.

I'm not complaining, I'm trying to learn what is going on.  How does one build a pedal that can flip phases like that (in other words, how did that happen?)  Or I guess maybe a better place to start would be why does the stratoblaster invert the phase like this?  There's a good chance that it is not some trait of all Stratoblasters, that it's just this particlar one.

So what is going on here?

[Kesh]

You can set up a stage (transistor or op-amp) to invert or not invert, by using the appropriate components and connections around them.

Transistors generally invert when you need voltage gain, as in many gain type pedals, and usually non-invert when you need current/impedance gain, often at the buffers at input or output. Typical inverting circuit is called a common emitter (or common source). Non-inverting is called an emitter (source) follower or common collector (drain).

Op-amps are more flexible and you get more choice over whether to invert or not.

Whether the pedal as a whole does or doesn't invert is down to how many inverting stages there are.

[Mike Burgundy]

-What Kesh said (typing simultaneously). It's part of the electronics, and in most cases more or less ignored since there are other design goals and inverting or not isn't an issue - until you run parallel lines, as you found out. The orange squeezer uses the + input of an opamp, so what comes out is in phase with that input (if you use the - input, the output is inverted - hey, that's a cool way for negative feedback! ;P )
The stratoblaster is a single FET booster, and as Kesh said, it inverts, because of the way a FET works. Put two stratoblasters in series and your back to (inverted inverted) in-phase.
If you were to set thet FET up as a 1:1 low output impedance buffer, you'd most likely take the signal from the source instead of the drain and it would NOT invert. The reason for choosing this instead of just setting the gain at 1 is usually NOT phase. Mostly, it's because the next stage wants to be driven by a low impedance, which a source (or emitter, in case of an NPN bipolar junction transistor) follower provides.

[lowvolt]

OK, while I don't totally relate to all of the nomenclature and the engineering terms as much as I'd like too, I totally understand the main idea.

Making a guitar with discrete pickup outputs has taught me things I would never have learned had I not had parallel pickup outputs.  So many things have come up and taught me new ~stuffs~.

Thanks for the help.  I'm not too far from fully comprehending these replies, I JUST NEED TO LEARN A LITTLE MORE ABOUT OPAMP AND JFET WORKINGS >>> SORRY ABOUT THE ALL CAPS MY KEYBOARD IS A PIECE OF SHYTE THAT HAS BEEN TRYING TO DIE FOR A COUPLE OF WEEKS NOW _____ IT"S LIKE THE SHIFT KEY GETS STUCK OR SOMETHING ... see .. there ... I whacked the hell out of the right-side shift key and it works properly again.

Anyhow, thank you.

[PRR]

> inverts, because of the way a FET works

Perhaps of interest:

If you want *both* voltage gain and current gain, ALL one-device amplifer stages invert. Tubes, BJTs, FETs whether J- or MOS-.

Exception: when you also have a transformer you can connect a winding either way. That's rare in guitar-cord work, once common in balanced microphone work. (And since a setup may have a mix of mikes who do not agree on polarity, a polarity-flip switch is common.)

If you only need voltage gain, you can run grounded-grid with no inversion. However the input impedance is way-low (no current gain).

As you say, when unity voltage gain is fine but current gain is needed, the cathode follower does the deed and no inversion.