Is a TrainWreck Out of Phase?

[billyz]

It would appear the Express is and out of phase amplifier. Counting the number of phase shifts in the circuit, the output is out of phase. Should the speakers be wired reversed to compensate ? Or does it make no difference?

I have a tube stereo amp and it too is out of phase . It makes a real difference to wire the speaker reversed to compensate. The manufacturer even instructs you to do so.

[hairyandy]

Phase, as you're referring to it in an audio amp, is relative. It really won't make much difference I don't think if you switch the speaker around with a Trainwreck. An example of this would be an amp that has two channels with differing gain stages like my 65 London. The EF86 channel is out of phase in relation to the 12AX7 channel because there is one more gain stage in the preamp. The only time that there is a problem is when you want to play both channels together, then you have to flip the phase on one channel.

There is an old recording trick, you reverse the phase of the monitors so that you can record vocals in the control room without headphones. when you flip the speakers back to listen, the bleed from the backing tracks is out of phase on the vocal track in relation to the rest of the song so that it cancels and you're left with just the vocal, at least in theory. It actually works really well.

Andy

[leaveitalone84]

Well I do know working from experience that phase in bass amps is important.

You want to be "in phase" with the bass drum.

[Fischerman]

Yes, the output is out of phase with the input. For guitar amps with a long-tail PI:
even number of inverting stages before PI = output in-phase w/input
odd number of inverting stages before PI = output out-of-phase w/input

In some amps with a switchable effects loop...the amp might be in-phase without the loop and out-of-phase with the loop (or vice versa)...then you have to know if the effect(s) in the loop reverse phase.

[Lonely Raven]

I've seen several threads on this in other forums, and I can see how this would matter. It would effect the attack, the initial movement of the cone, and being in/out of phase with other instruments.

From a guitar standpoint, I've been told it can drastically effect feedback and sustain.

It's not difficult to wire you speakers out of phase and see if it makes a difference for yourself!

[funkmeblue]

according to the june 1992 guitar player article.....trainwreck amps are designed to be phase coherent-i.e the input signal is in phase with the output signal.

[leaveitalone84]

I've seen several threads on this in other forums, and I can see how this would matter. It would effect the attack, the initial movement of the cone, and being in/out of phase with other instruments.

From a guitar standpoint, I've been told it can drastically effect feedback and sustain.

It's not difficult to wire you speakers out of phase and see if it makes a difference for yourself!

If the amp is out of phase the amp sound waves would dampen the guitar sound waves. So yes lack of feedback and sustain would probably be heard and felt.

Thats how noise cancelation head phones work.

[hairyandy]

I've seen several threads on this in other forums, and I can see how this would matter. It would effect the attack, the initial movement of the cone, and being in/out of phase with other instruments.

From a guitar standpoint, I've been told it can drastically effect feedback and sustain.

It's not difficult to wire you speakers out of phase and see if it makes a difference for yourself!

If the amp is out of phase the amp sound waves would dampen the guitar sound waves. So yes lack of feedback and sustain would probably be heard and felt.

Thats how noise cancelation head phones work.

What? The amp sound waves would dampen the guitar sound waves?!? The only sound wave you're hearing is coming out of the speaker and there is nothing else to cancel it. You're not going to have any lack of sustain or feedback. To illustrate this, make a speaker cable that has the positive and negative flipped on one end. Now use it between your amp and cab and play through it. Then substitute that for a normally wired speaker cable. You won't hear much difference as long as you're playing one sound source through one amp and one cabinet.

BTW, the way that sound canceling headphones work is that they feed the outside noise to you out of phase (via a small mic) so that it cancels and all you hear is what's left, ie: the sound from your iPod or other device.

Andy

[leaveitalone84]

I've seen several threads on this in other forums, and I can see how this would matter. It would effect the attack, the initial movement of the cone, and being in/out of phase with other instruments.

From a guitar standpoint, I've been told it can drastically effect feedback and sustain.

It's not difficult to wire you speakers out of phase and see if it makes a difference for yourself!

If the amp is out of phase the amp sound waves would dampen the guitar sound waves. So yes lack of feedback and sustain would probably be heard and felt.

Thats how noise cancelation head phones work.

What? The amp sound waves would dampen the guitar sound waves?!? The only sound wave you're hearing is coming out of the speaker and there is nothing else to cancel it. You're not going to have any lack of sustain or feedback. To illustrate this, make a speaker cable that has the positive and negative flipped on one end. Now use it between your amp and cab and play through it. Then substitute that for a normally wired speaker cable. You won't hear much difference as long as you're playing one sound source through one amp and one cabinet.

BTW, the way that sound canceling headphones work is that they feed the outside noise to you out of phase (via a small mic) so that it cancels and all you hear is what's left, ie: the sound from your iPod or other device.

Andy

I understand the physics of the noise canceling headphones. But it can be applied to large scale outdoor areas as well. Highways, metros, airports etc.

I know for a fact that if my bass amp was out of phase with a drummer the impact would be a lot less. It's especially apparent with my upright.

If your amp is putting out an out of phase signal than what your guitar is putting out, and your blasting your amp at your guitar. There has to be some sorta of canceling on one level or another.

[dartanion]

Phase issues can happen for a variety of reasons, and this can be demonstrated easily and very non-scientifically. I think everyone has done the "sweetspot" search during sound checks for optimal feedback. There are also deadspots too. You can also do this in a room as you are listening too. Then, to further screw things up, fill the room full of people and listen for what happens.

This topic has been discussed ad nauseum here and on other forums.

[jaysg]

I'm not sure this is something to over analyze. Your pedals may invert when kicked in vs. out. Somebody here (ScottL or Richie or ?) carries a speaker wiring inverter with them and I guess, sets up and tries it both ways, then settles on one.

[dBe]

In the EBS (esoteric bullsh--) department, the important thing to remember is that transients - sharp leading edges - are more faithfully reproduced when the speaker cone moves away from the cabinet when the note (or sound) begins. Air, being compressible, is easier to push than it is to pull. The ear is capable of hearing the difference in transient "speed" between compression and rarifaction events. Sound in nature begins with a positive pulse leading (compression).

Punch comes from a leading edge positive waveform. Having a speaker move away from the listener at the beginning of a note, well, sucks. This is particularly noticeable in low frequencies. The leading edge on the waveform from a concert drum tuned to 10Hz is felt, not heard. Imagine what that would be like if it was rarifying (sucking) instead of compressing.

Easy to hear: change the the speaker polarity back and forth and hit chords hard. The punchy sound is the compression mode of the speaker connection. The lifeless one is when the speaker sucks. Or, so to speak

TMSAISTI

Dave

[nickt]

Just remember you can blow as hard as you like, but you can only ever suck at 14psi. Here endth the lesson...

[geetarpicker]

I think that phase can have effect on controlled feedback. That said, I don't think there is one good way and one bad.

Recently I was experimenting with trying to get a particular note on my LP to sustain through my Wreck. I was trying to find the absolute lowest volume level (with a power attenuator in line) I could get away with and still get the note to predicably sustain. I found that this one particular note was easier with the phase reversed by using a rewired speaker cord. I also found that some notes sustained better with the phase "as is", and other notes worked better with the phase reversed. It's frequency dependent. I'm almost considering making a switch box to control this on the fly for song to song control, but making this safe without putting the amp in standby is the issue.

In other words moving your guitar position in relation to the amp, the phase of the amp AND the particular notes themselves all play a part in high volume and/or high gain sustain.

[leaveitalone84]

I had a thought.

What if you reverse the guitar chord? Have a little stompbox that switches the phase of the guitar signal.

Or does it need to be at the speaker level?