Output Transformer polarity whats up

[paulster]

Celestions move out with positive applied to red, so I'd consider that normal rather than backwards.

[Structo]

Got a question, Tony. How do you test to see if the windings are wound opposite to what would be "normal?" And, if that is the case, if the magnet is also backwards, you get the same overall polarity of the induced signal on the secondary. Not sure if you mean just the windings.

Cheers,

Gil

That would be my question as well.
I have seen the dot on transformer schematics for the wiring code but don't really remember what it signifies.

I too wonder what role the polarity of the transformer plays but, I don't think the polarity of the secondary is the same as the polarity of the primary, thus you don't get positive feedback on the primary side when you flip the secondary polarity.
You just have to be careful to not reverse it at the amp, since the ground lead of the secondary is typically grounded to the chassis.

I don't think picking direction of the string would affect the phase.
The amp doesn't know which way you are picking, just that a signal was generated at the input.

The thing I took away from the previous threads about this was it seemed to do more with how many stages of amplification there are before the phase inverter (LTPI).

Does the phasing of a push-pull amp become a pull-push amp if the speaker is out of phase?

Also does the number of stages before the phase inverter affect the phasing to the speaker?
For instance, if you have three stages before a LTPI is the output going to be 180 degrees out of phase?
If you have two preamp tubes equaling four stages before the phase inverter, would that guarantee the phase to the speaker is correct?

Anybody know if the EVM 12L speakers are correctly phased?
I seem to remember checking them with a 9v battery, so it must have been ok as I didn't change anything.

I think I will make a switch box that flips the speaker leads to see how it affects the sound.

[paulster]

That would be my question as well.
I have seen the dot on transformer schematics for the wiring code but don't really remember what it signifies.

The dot is a notional representation of the start or end of the winding. It could be either, as it's only to signify the relative polarity between primary and secondary windings.

I always check out new OTs on the scope to double-check and/or identify the relative polarity between primary and secondary so that I can install them and cut the wires without having to worry about the dreaded positive feedback squeel and then desoldering and lengthening leads, and generally messing up a tidy install. It's really quick and easy to do on a dual-channel scope using the 1kHz square wave built in without having to hook up an external signal generator.

I too wonder what role the polarity of the transformer plays but, I don't think the polarity of the secondary is the same as the polarity of the primary, thus you don't get positive feedback on the primary side when you flip the secondary polarity.

If you flip the phase of the secondary then you will swap from negative feedback to positive feedback, just as you would if you swapped the grid wires and flipped the phase at the primary side. It doesn't matter where you flip it, if you flip it it's flipped!

I don't think picking direction of the string would affect the phase.

See earlier comment. The string direction towards or away from the pickup determines the polarity of the wave, not the direction in the vertical plane.

The thing I took away from the previous threads about this was it seemed to do more with how many stages of amplification there are before the phase inverter (LTPI).

True, because now you're talking about the polarity of the amp as a system. Each plate-coupled triode stage is inverting, so in a three-stage amp you'll have an inverted/non-inverted/inverted again signal hitting the PI. Assuming a long-tailed PI and a Marshall-style presence and NFB connection then the PI and output stage is non-inverting overall, so the overall system is inverting.

Remove NFB like a Matchless, Rocket or AC30 and it's anybody's guess because there's no requirement to connect the primaries of the OT round any given way.

[Zippy]

There was a big TGP debate about this with Steve Kimock getting very passionate about how it worked 'his' way, even when proven the opposite was true with scope capture plots.

Essentially the polarity is determined by the string movement towards or away from the pickup, not up or down.

Whichever way you pick, up or down, you initially press the string towards the pickup, so a note will always begin with the same polarity. The only likely exception to this would be popping, but that's really for the 4-stringers. Then it's just a question of which way your pickups are wound or which direction the magnets face.

Thanks, Paulster.

That's not sufficiently satisfying but that's my issue. It seems that any movement in the plane of the magnetic flux should not generate any voltage. Pickups work because the strings are crossing lines of flux.

What of when one does a pinkie swell on a note? Does speaker polarity still matter if you do not hear the attack? I visited Bill Bartolini years ago and saw one of his pickup testing machines - the strings were magnetically driven so no attack was needed or present and he got a constant known displacement from which to evaluate pickup output. We did not discuss psychoacoustics so I don't know his take on that.

[BobW]

The dot is a notional representation of the start or end of the winding. It could be either, as it's only to signify the relative polarity between primary and secondary windings.

Actually it's the relative polarity between any windings, primary and secondary.

[Structo]

I don't believe that if you wire a speaker cable reversed, that it would cause positive feedback to the PI. It would be the same as flipping the wires on the speaker.
Speakers don't really care which they are wired, but our ears do.

When we talk about generating positive feedback and getting that nasty howling or squealing, that is either because the primary OT wires or grid wires are reversed.

When I stated "flip the secondary polarity", I said it wrong.
I mean, reverse the polarity to the speaker, not change the OT secondary tap wiring, that would short out the speaker wouldn't it?

[hitchcaster]

i guess i should of kept it simple, but the only thing that i was trying to add to the conversation was that people might benefit from have a way to reverse the polarity on their speaker cables. you can't do that with a battery, thats only for getting different speakers in phase with each other. each gain stage flips the phase, so add the dumbleator and its different. the speaker brand/model thing is confusing.. same with pickups.. actually pickups is more confusing cause there's two ways to flip the phase and they don't sound the same.

[talbany]

Been doing some more reasearch on this topic calling around cannot find a definitive answer as some of this really makes no sense so far..The odd thing is output transformers in theory should not become magnetic due to it's high steel content..However I am getting a North south reading on my pickup Polarity checker..Not a strong one but one none the less..The 2 amps I have here that had phasing issues were fender Super Twin and a Silverface Bassman...these read south and benefited greatly by reversing speaker polarity..
How I understand it ... Transformer in a mono push pull amp is constantly changing polarity 60 times a second between the 2 primary's or 2 tubes reversing the phase here changes the direction of the cone but as Gil states doing this can cause positive feedback via the presence circuit..Also swappin then at the PI results in the same effect....We know that the internal phasing generated by the guitars pickups North South or direction of the wind as well as the the internal phasing shifts that take place in the amp including a loop which I did try and noticed no real change and didn't in my case seem to effect speaker polarity...The only explanation I can think of can be if the primary wires are wound opposite which is a strong possibility...This may be why I am showing the opposite polarity as well
The 2 amps I switched here made a noticeable improvement
Please no attacks here as I am trying to figure out whats going on here as well..Let keep it constructive

Tony VVT

[heisthl]

I think it depends on how far away your guitar is from the speaker. A sine wave through an amp/speaker sounds the same to my ears regardless of polarity at the speaker. I've noticed speaker polarity is more noticeable when you stand at different distances when you're playing. Like the guitar is getting a more positive feedback from the speaker when the distance is right and that improved response distance changes when the speaker polarity is reversed.

[Zippy]

I think it depends on how far away your guitar is from the speaker. A sine wave through an amp/speaker sounds the same to my ears regardless of polarity at the speaker. I've noticed speaker polarity is more noticeable when you stand at different distances when you're playing. Like the guitar is getting a more positive feedback from the speaker when the distance is right and that improved response distance changes when the speaker polarity is reversed.

That's an interesting observation to chase. By noting the distances, one may deduce the frequencies that are active. Seems like they should be pretty low frequencies tho'. Something to do with resonant frequency of the guitar more than something in the amp?

[paulster]

The 2 amps I have here that had phasing issues were fender Super Twin and a Silverface Bassman...these read south and benefited greatly by reversing speaker polarity..

What's the overall system phase of these amps versus a reference amp? Are they both inverting or non-inverting? I'm wondering if you're finding a preference for one particular system phase which is working better for you in conjunction with your guitar, pickups and cabs.

Changing the polarity on a speaker cable certainly makes an audible difference, particularly to sustain where constructive feedback can become destructive feedback, and so on.

How I understand it ... Transformer in a mono push pull amp is constantly changing polarity 60 times a second between the 2 primary's or 2 tubes

It's changing polarity at the frequency of the signal applied, so a power tranny would be 60 times a second whereas an OT would be at audio frequencies.

Any magnetic field escaping the transformer would also be swapping polarity at this rate, so I'm surprised you can get a signal one way or the other unless the output is heavily skewed in favour of one half of the winding, i.e. via an unbalanced PI or an asymmetric signal (caused by clipping stages earlier in the amp or by the PI design), which would mean that one half of the waveform was dominant.

[BobW]

...The only explanation I can think of can be if the primary wires are wound opposite which is a strong possibility...

I doubt the OT was taken off the winding jig, then reversed 180 during manufacturing. It's more plausible to assume the start and finish (dot or no dots) are reversed on the primaries or were at least connect that way. Primaries are usually 2 coils wound in steps to increase coupling and efficiency. A simple case other than complex interleaving is: The 1st primary coil is wound, then the secondary coil is wound, then the 2nd primary coil is wound. The 2 primary coils are then connected together to form the CT. It makes more sense that the 2 primary winds were connected wrong during manufacturing not reverse wound. constructive eh?

[talbany]

...The only explanation I can think of can be if the primary wires are wound opposite which is a strong possibility...

I doubt the OT was taken off the winding jig, then reversed 180 during manufacturing. It's more plausible to assume the start and finish (dot or no dots) are reversed on the primaries or were at least connect that way. Primaries are usually 2 coils wound in steps to increase coupling and efficiency. A simple case other than complex interleaving is: The 1st primary coil is wound, then the secondary coil is wound, then the 2nd primary coil is wound. The 2 primary coils are then connected together to form the CT. It makes more sense that the 2 primary winds were connected wrong during manufacturing not reverse wound. constructive eh?

Paul at MM mentioned that some Fender transformers they blue printed were opposite polarity with respect to the primary than others (Blue and Brown..does this make sense)..Don't know if this was due to a mistake or intentionally reversed it..Fender did some some strange things in the Silverface era bringing in the HiFi engineers (Big on reversing phase) after CBS..Is it also reasonable to believe that the north south polarity reading is related to the direction of the winds on the primary and be some kind of clue as to output polarity....... If they were using JBL's at the time wound them this way to compensate for the different polarity there as well...The 2 amps here are Silverface era and doubt both were mistakenly constructed.... Constructive right back..

Tony

[talbany]

It's probably a good idea at this point to broaden the test field of output transformers before we draw any conclusions and see if this applies only to this era Schumacher...I'll keep researching and post them if I find any definitive results and hope others do the same..Thanks for the replies everyone..


Tony

[ayan]

Whichever way you pick, up or down, you initially press the string towards the pickup, so a note will always begin with the same polarity. The only likely exception to this would be popping, but that's really for the 4-stringers. Then it's just a question of which way your pickups are wound or which direction the magnets face.

I don't want to sound argumentative, but I am argumentative. Seriously, to me, when picking down the string is squeezed towards the pickups and when picking up it gets pulled away from them. If you anchor your hand and move from the wrist, which is at least what I do, I believe it's easy to see that by following the movement of the tip of the pick (which in a perfecet world would travel on a circle). The exception would be if I were to pick with my hand glad over the string, in which case picking up and down would simply drag the string away from the polepiece in opposite directions. As it were, when I pick my hand is not flat against the strings, such that on a downstroke the pick travels down on the the plane of the top of the guitar as well as down into the guitar body. The closer I get to the 1st string, the flatter my hand gets, but when I pick on the 6th string my hand is definitely roatated about my forearm's axis ("roll" angle, if you will).

Cheers,

Gil