Output Transformer polarity whats up

[Zippy]

Worth saving:

For completeness though the direction of the initial attack will depend on:
- whether your picking motion pushes the string towards the pickup or away from it as you strike it,
- the winding and magnet direction of the pickup,
- the number of gain stages in the amp,
- the effect of any pedals or other effects (e.g. the Dubleator) en route,
- which way round the OT is connected in a non-NFB amp and finally
- the polarity you choose for your speaker wiring.

[greiswig]

Tom wrote:

And it also seems that if you are playing in a band with a bass and another guitar, if your speaker is out of phase with the others will that cause problems or not?

Say you all play an open E (Bass, second fret on D string), how will that sound if one or two speakers are out of phase with the other players?

and...

I have read here that it depends on how you pick or strike the strings and that pushing the string towards the pickup results in a positive wave.
But, how many of us pick a string so the string goes towards the pickup?

My .02$, Tom...neither of these matters. Have you played in an acoustic setting, where you're playing acoustic guitar with other acoustic guitars? Does it make a lick of difference in the sound whether you're both facing the same direction or facing each other in a circle? Because that *should* theoretically change the phase. But it makes virtually no difference...because you're all playing different notes, even if those notes are in tune with each other. What little destructive interference there is is pleasing to the ear, not the same as if you were playing the exact same instrument and note through a pair of speakers that are out of phase with each other.

Similarly, I think it a mistake to think of a string as either going up-down or side-side relative to the pickup. When you pluck a string, the axis of the sine wave along the string will rotate on the axis of the string. It's not going to be stable and only move in that one direction.

All this said, I installed a polarity switch on my amp (insulated both leads from ground), and I can definitely hear/feel a small difference in the sound. I prefer it "positive polarity," but then I'm not using a dumbleator and I don't know if the effects loop I'm using inverts the signal or not. I don't know what might cause this effect, and I wonder if anyone else who is more than a few feet away from the amp could hear it: if it is a result of hearing two sources (the resonance of the guitar conducted through bone to your ear (at mebbe -122db!) relative to the amp), that might explain it...I don't know. I bet an amplified violinist would be more able to hear that difference, though.

[greiswig]

I just happened to think...the amp hears, too. Even the best tubes are probably slightly microphonic, so if your amp is on or near your cabinet, I bet the phase of the speakers affect the way the cabinet resonates relative to the tubes, and that acoustic feedback loop would be affected. So perhaps that's why we hear a difference when the polarity is switched. That would be pretty easy to test, too.

All this said, I installed a polarity switch on my amp (insulated both leads from ground), and I can definitely hear/feel a small difference in the sound. I prefer it "positive polarity," but then I'm not using a dumbleator and I don't know if the effects loop I'm using inverts the signal or not. I don't know what might cause this effect, and I wonder if anyone else who is more than a few feet away from the amp could hear it: if it is a result of hearing two sources (the resonance of the guitar conducted through bone to your ear (at mebbe -122db!) relative to the amp), that might explain it...I don't know. I bet an amplified violinist would be more able to hear that difference, though.

[Structo]

Yeah, bottom line it's probably much a do about nothing.
Just thought my observations were interesting because I remember having this discussion.
But that was before I experimented with the D'lator.

Having a phase switch would be the way to go so you can instantly hear the change.

Did you use a special make before break type switch or just a common toggle?

[greiswig]

Yeah, bottom line it's probably much a do about nothing.
Just thought my observations were interesting because I remember having this discussion.
But that was before I experimented with the D'lator.

Having a phase switch would be the way to go so you can instantly hear the change.

Did you use a special make before break type switch or just a common toggle?

I just used a common toggle, but you'll want to put the amp in standby for a bit before switching. Better safe than fried.

I'm not sure about the much ado about nothing, though: that little light bulb that went on over my head about the microphonic nature of the amp circuit itself and sitting on or near the cabinet is still on. I just wonder if that (the effect of phase on the acoustic feedback loop between amp and cabinet) isn't the primary source of the difference we hear. But I guess my theory is that it doesn't have anything in particular to do with absolute phase.

[Zippy]

I just used a common toggle, but you'll want to put the amp in standby for a bit before switching. Better safe than fried.

I agree. A make-before-break switch means that you would be shorting the output.

I'm not sure about the much ado about nothing, though: that little light bulb that went on over my head about the microphonic nature of the amp circuit itself and sitting on or near the cabinet is still on. I just wonder if that (the effect of phase on the acoustic feedback loop between amp and cabinet) isn't the primary source of the difference we hear. But I guess my theory is that it doesn't have anything in particular to do with absolute phase.

I'm curious about that as well. Seems you should just be able to rotate a head on top of the cabinet to see/hear what it does. Of course, some (such as geetarpicker) take the head (Trainwreck Express) off the cabinet to eliminate those interactions.

[greiswig]

Seems you should just be able to rotate a head on top of the cabinet to see/hear what it does.

I don't think that would do it: the cabinet is not vibrating front-rear or anything like that such that turning the backward would affect its relative phase. In a sealed or semi-sealed cabinet, it might be more akin to compression/expansion in every direction.

Heck, in a really resonant cab, it might behave more like an acoustic guitar, such that you could see Chladni patterns at given frequencies.

But removing the amp from the cabinet altogether and separating it by a good bit certainly would eliminate the interaction if there were one.

[Structo]

It seems logical too that if the speaker is in a sealed box, the phasing would be even more important because of the compression of the air in the box.
So if the speaker cone moves back on the attack of a note, it is fighting the air suspension.
Seems to me that it would sound different than if the cone pushed out on the attack.

I thought that this topic would generate a lot more interest.
Since it would affect anybody playing through an amp.
Because it seems that any amp that has an even number of stages is going to have the phase inverted at the speaker.
Either everybody knows all about this or they don't feel it is an important issue enough to discuss it.

[paulster]

It seems logical too that if the speaker is in a sealed box, the phasing would be even more important because of the compression of the air in the box.
So if the speaker cone moves back on the attack of a note, it is fighting the air suspension.

It will fight to compress the air when it moves backwards just as hard as it fights to expand the air in the enclosure when it moves forward.

That's how speakers work. They don't express a preference for which direction the cones move in since they are designed to handle AC signals.

Can we please move on from this particular ridiculous notion before people actually start to believe it?

[Structo]

I don't think proper speaker phasing is ridiculous at all.

There is a difference in the way the speaker sounds.

Try it yourself and listen.

[paulster]

I don't think proper speaker phasing is ridiculous at all.

There is a difference in the way the speaker sounds.

Try it yourself and listen.

Proper speaker phasing is perfectly sensible, but to suggest that a speaker has a physical preference for a particular signal polarity is, just that, ridiculous.

Put a pre-recorded signal into a single speaker and then flip its phase and tell me you hear a difference.

You won't.

You hear a difference when you're playing guitar because you get either constructive or destructive acoustic coupling at certain frequencies, which can help produce feedback or dampen it.

That's because the overall system from guitar through effects, amp and speakers is acting as just that, a system. Changing the phase at the speakers or anywhere else in the chain will have an effect on the system as a whole, because of the coupling that's occurring between speaker and guitar, which is like global (negative or positive) feedback outside the amp.

So that's exactly what you want to focus on, and the relative merits thereof, not the physical characteristics of drive units themselves.

I have tried flipping phase many times, not least because my isolation transformers for running stereo rigs all have phase switches in them, so it's a push-button operation to try.

I always find that if I flip the phase of a single amp in isolation the feedback will increase of decrease, but I can move to another position and get the exact opposite effect.

This particular effect is also why you'll see the likes of Carlos Santana and Gary Moore having taped crosses on their stages, so they know where to stand to pull off the infinitely sustained notes.

[Structo]

Well I think it may be important to have all my amps and speakers in phase.
I frequently will run two amps using the stereo outputs of a few pedals I have such as reverb, delay, chorus.
If the two sets of speakers or amps are not in phase then you get cancellation or just plain bad sound.

So for me, I like to know that my speakers are all pushing air at the same time and not one pulling and one pushing.

Anyway, this is how we learn by sharing information and discussing things without injecting emotions into the conversation.

[greiswig]

Well I think it may be important to have all my amps and speakers in phase.

I don't think I would have put it quite as...succinctly...as Paulster, but I think his point is valid, Tom: what I'm saying is that I don't think there is such a thing as "in phase" for a single source. There might be a feedback loop such that one phase or the other is preferable, but don't bet on your preference being "in phase."

A good acoustic DI will have a phase switch on it to help with feedback control through a monitor system. Doesn't change the sound of the instrument a bit to the audience. There is no absolute phase.

I do think this is an interesting topic, and worthy discussing. My theories (at least) are just that...and probably merit reasonable retorts from those more knowledgeable than I.

[greiswig]

I had the opportunity to test my hypothesis a bit: in our large room at church, I opened up the amp quite a bit and played first with the head on the cabinet, then with the head about 10' away on the floor. For both situations, I played with the phase switch in both positions, for a total of 4 conditions.

Results: with the amp on the cabinet, the distinction between phases was pretty clear. One phase in particular was easier to generate feedback from and punchier overall. With the amp removed from the cabinet, the distinction between the two phases was much less clear, and really seemed to relate to the sensation I had from the guitar itself (i.e. what I was hearing/feeling from the guitar directly).

So I think this supports my idea that there is a feedback loop between the cabinet and the tubes/circuit that could be either positive feedback or negative depending on the polarity of the cabinet. But I'd like to have some other people try the experiment themselves.

[talbany]

I had the opportunity to test my hypothesis a bit: in our large room at church, I opened up the amp quite a bit and played first with the head on the cabinet, then with the head about 10' away on the floor. For both situations, I played with the phase switch in both positions, for a total of 4 conditions.

Results: with the amp on the cabinet, the distinction between phases was pretty clear. One phase in particular was easier to generate feedback from and punchier overall. With the amp removed from the cabinet, the distinction between the two phases was much less clear, and really seemed to relate to the sensation I had from the guitar itself (i.e. what I was hearing/feeling from the guitar directly).

So I think this supports my idea that there is a feedback loop between the cabinet and the tubes/circuit that could be either positive feedback or negative depending on the polarity of the cabinet. But I'd like to have some other people try the experiment themselves.

That's great info and definitely sounds like the anomaly I was hearing.. I did have the amp on the cab when experimenting with polarity.. when I get the chance I will try the same with the amp removed and report the results.. Now we are getting somewhere!!

So the effects in a combo would be enhanced!!

Tony