In or out of phase?

[Swampertech]

Gentlemen, is this amp out of phase, and if so could I remove V4A to be in phase at the PI? Thank you for your input!

[sluckey]

Gentlemen, is this amp out of phase, and if so could I remove V4A to be in phase at the PI? Thank you for your input!

Talking about the two inputs??? They are in phase at the point where they are mixed together.

[shooter]

appears the input jack will be outta phase with FX out if that's a concern 

[Swampertech]

Steve and Shooter, I was referring to amp input phase as compared to amp output phase.

[shooter]

I have the input outta phase with PA tubes output, but what happens through the OT depends. speaker wires I believe can be flipped to "fix" phase.  I was concerned early on but got convinced it don't matter

[sluckey]

Steve and Shooter, I was referring to amp input phase as compared to amp output phase.

Who cares? Never heard anyone want to know that. If you think it makes a difference, just flip the wires at the speaker.

[jjasilli]

Steve and Shooter, I was referring to amp input phase as compared to amp output phase.

This is a recurrent topic.  +1 to sluckey.

[PRR]

> is this amp out of phase

Insufficient data. (OT has no dots.)

Also the plan is not the amplifier. (You could have cross-wired something in the output stage.)

And way too many stages for me to even try to work out.

If you have some reason to "need" absolute phase, you can hear a difference, try it both ways and see what you hear.

[2deaf]

Input is out of phase with output. 

Input:  UP
V1 or V1B:  DOWN -- inverts
V2A:  UP -- inverts
V2B:  UP -- doesn't invert
V4A:  DOWN -- inverts
Metropoulos Loop:  DOWN -- doesn't invert.  A bypass switch also wouldn't invert.
V5A Grid:  DOWN
Output:  DOWN -- V5A Grid is in phase with the NFB from the output.

[sluckey]

How can you say that without knowing how the OT is connected?

[2deaf]

How can you say that without knowing how the OT is connected?

Sooner or later they always end up with the Output in phase with the input to the LTP PI when NFB is used.  Otherwise the amp will have positive feedback. 

[shooter]

Sooner or later they always end up with the Output in phase

The upside to PP amps, no such luck in xSE, ya gotta scope it, well you don't since it's mostly a moot point.
I do think having the FX return being IN phase with input is probably something to consider 

[jjasilli]

How can you say that without knowing how the OT is connected?

Sooner or later they always end up with the Output in phase with the input to the LTP PI when NFB is used.  Otherwise the amp will have positive feedback.

Yes, but NFB could be injected anywhere, or in multiple places (though this in not usual for guitar amps).  Obviously by definition the NFB must be negative, or out of phase, with signal at the point(s) of NFB injection.  Signal phase at the input jack is not relevant. 


(It should be noted that +/- phase is a useful over-simplification.  It's true for typical gain stages.  But meanwhile, intermediary R-C circuits rotate phase in 90 degree increments or multiples thereof; and may do so only for certain bands of the audio spectrum.  The unwanted result is that some of the feedback signal may be negative, while other parts are in-phase enough to cause positive feedback, unless the NFB is suitably filtered.)

[2deaf]

Yes, but NFB could be injected anywhere, or in multiple places (though this in not usual for guitar amps).

The statement was specific to Swampertech's schematic which has the NFB injected at the grid of V5B.

Obviously by definition the NFB must be negative, or out of phase, with signal at the point(s) of NFB injection.

Swampertech's LTP PI amplifies the difference between the signal at the grid of V5A and the signal at the grid of V5B.  Injecting a signal at the grid of V5B that is in phase with the grid of V5A decreases the difference between the two grids and the gain decreases.  The fact that the feedback signal reduces the gain defines the feedback as negative.

[sluckey]

If you put his two posts together you'll see he has commented about two different things.

is this amp out of phase, and if so could I remove V4A to be in phase at the PI?

I was referring to amp input phase as compared to amp output phase.

I don't think he knows what he's asking any more than we do.     No wonder there are answers all over the place. No matter, he likes everything everybody has said.   

[Swampertech]

I don't think he knows what he's asking any more than we do.     No wonder there are answers all over the place. No matter, he likes everything everybody has said.   

Steve, I was just asking a question concerning an amplifiers' input phase as compared to its output phase. In most of the audio circuits I'm familiar with, phase can have a significant effect on the total sound of the device. When I saw 2deaf's post talking about phase, I just thought I'd post the question to see what the experts would say concerning guitar amps. Sorry if I offended you, or anyone else.

{EDIT - fixed broke quote -PRR}

[sluckey]

You didn't offend me. I'm tougher than that. 

[shooter]

IF you had a stereo Gamp and enough separation then phase might matter.  I just finished a 5ch stereo and DID check phasing.

I asked  exactly the same thing here early on since my whole career cared ALOT what phase was doing so.......

here's a quick learner so you can check a transformer and add your own dots 
 https://www.allaboutcircuits.com/textbook/alternating-current/chpt-9/phasing/

[jjasilli]

IF you had a stereo Gamp and enough separation then phase might matter.  I just finished a 5ch stereo and DID check phasing.

In this case it's the output of the speakers which should be in phase with each other.  Actually, I think less separation would cause more sound cancellation.  If the speakers were a 100 feet apart and out of phase, there would be no cancellation.  There would be lots of cancellation if they were in the same cabinet.

This is not relevant to signal phase at the input jack, or elsewhere inside the amp.  Also, placement of the speakers within a room alters phasing significantly and can override their electrical phase.