Amp Phase - Am I going mad?

[Littlewyan]

I've always read that a Trainwreck Express is in phase and I've taken that as the output is in phase with the input, however looking into it I don't think that's true? If you go through the gain stages it seems that the output is out of phase with the input.

Also reading some information written by Ken Fischer regarding the JTM45 he says they are out of phase. But again, go through the gain stages and you'll see that they are in phase?

https://books.google.co.uk/books?id=kxt ... se&f=false

Am I looking at this wrong? The output of a LTPI Power Amp will be in phase with the input of the LTPI, so if you have an even number of gain stages prior to it then the output will be in phase with the input, is that right?

[Stevem]

I may be wrong, but off the top of my head I would say both amps are out of phase at the speaker input!

[Littlewyan]

How so? A JTM45 has one less gain stage (cathode follower won't flip the signal)

[norburybrook]

Phase is always relative so does it matter? if you have more than one amps then yes


M

[martin manning]

My reckoning is that the speaker output on the Express is out of phase with the guitar input, and in phase with it in the case of the JTM45. People have claimed to hear a difference when swapping the speaker leads on a combo amp, which I think might have to do with feedback from the speaker to the amp chassis and its electronic components.

[frankdrebin]

I think i have read somewhere (maybe the Doyle Marshall book) that jtm45 and Bassman were opposite phase,i think the speakers were reverse polarity in Marshall.

[frankdrebin]

By my reckoning is that the speaker output on the Express is out of phase with the guitar input, and in phase with it in the case of the JTM45. People have claimed to hear a difference when swapping the speaker leads on a combo amp, which I think might have to do with feedback from the speaker to the amp chassis and its electronic components.

i think so,when you pick at loud volume,the first impulse is the biggest and in an open back cab in a small ambient can really make a difference because of reflections having different timing.

[pdf64]

I agree with your analysis, the JTM45 looks to have its output in the same polarity as its input, whereas with the Express (having an additional inverting gain stage), its output looks to be in opposing polarity to its input.
Note that when implementing a circuit, it's trivial to flip signal polarity at the speaker jacks, provided a type that is isolated from the chassis is used.

[norburybrook]

I agree with your analysis, the JTM45 looks to have its output in the same polarity as its input, whereas with the Express (having an additional inverting gain stage), its output looks to be in opposing polarity to its input.
Note that when implementing a circuit, it's trivial to flip signal polarity at the speaker jacks, provided a type that is isolated from the chassis is used.

I think matchless combo's had a speaker phase switch.

M

[Colossal]

I agree with your analysis, the JTM45 looks to have its output in the same polarity as its input, whereas with the Express (having an additional inverting gain stage), its output looks to be in opposing polarity to its input.
Note that when implementing a circuit, it's trivial to flip signal polarity at the speaker jacks, provided a type that is isolated from the chassis is used.

I think matchless combo's had a speaker phase switch.

M

I added a switch to the back of a 4x12 to phase flip when using an Express

[Littlewyan]

Ok so we've established that the Express is indeed out of phase with the input, so why does Ken say it's in phase? And then say the JTM45 is out of phase?

[frankdrebin]

Ok so we've established that the Express is indeed out of phase with the input, so why does Ken say it's in phase? And then say the JTM45 is out of phase?

Because he used the magic property of the vacuum cleaner cord? Lol

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[martin manning]

Ok so we've established that the Express is indeed out of phase with the input, so why does Ken say it's in phase? And then say the JTM45 is out of phase?

Source? Are you sure it wasn't (and correctly) the other way around?

[norburybrook]

Interestingly.....or not... I used my Express with my #102 and they were both in phase at the speaker.

Marcus

[Littlewyan]

Admittedly I can't find the source for the Express being in phase, maybe I heard it from someone on here. However in the original post you'll find a link to a Gerald Weber book where Ken says the JTM45 is out of phase.