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What does this mean?


 
3/9/2004 11:21 PM
Bommel What does this mean?
Hi all!  
 
I read something and don´t quite understand what is meant:  
 
quote:"Trainwreck amps are designed to be "phase coherent"-I.e., the input signal is in phase with the output signal."  
 
Can anyone explain this to me?  
Thanks!  
 
Bommel
 
3/9/2004 11:55 PM
Don Symes
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It means, at least in intent, that the positive-going part of an input signal will push out on the speaker cone and the negative-going part will pull it in.  
 
In theory this helps improve sustain/feedback.
 
 
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3/10/2004 12:50 PM
Le Basseur
quote:
"the positive-going part of an input signal will push out on the speaker cone and the negative-going part will pull it in"
 
IMHO it's the "absolute phase" story,wich in this case means a non-inverting amp.As you maybe know,each amplification stage in a given amp is rotating the phase so it's a very common problem encountered by mixmen. For guitarists who'd want to take their amp's signal both from line out AND mike in a studio or stage situation it's a real issue,because if the line out is,say,in phase with the input but the loudspeaker is out of phase,there are some serious cancellations there!:)  
I cannot see though,what's the possible link between a "phase correct" amp and sustain/feedback.
 
3/10/2004 2:02 PM
Newt
email

"I cannot see though,what's the possible link between a "phase correct" amp and sustain/feedback."  
 
I would agree with that! I would think that sustain/feedback would be a result of the mechanical sound wave from the speaker causing the strings/body of the guitar to vibrate. I calculate that the wavelength of the fundamental of the "C" on the first string is about 2 feet. So even if you know whether your output is "in phase" or "out of phase" with your input, you'd have to be the proper distance from the speaker for this to have an effect.
 
3/10/2004 3:02 PM
Allen
Presumably, when the string is moving toward the pickup, the amplitude of the wave is increasing, as the string moves away, the amplitude is decreasing. This amplitude modulation by the string generates the waveform that is amplified by . . . the amplifier. Which way does the cone move for perturbations where the string is moving towards the pickup?
 
3/10/2004 3:47 PM
Le Basseur
quote:
"This amplitude modulation by the string generates the waveform "
 
Ahm...  
?!?;)  
quote:
"Which way does the cone move for perturbations where the string is moving towards the pickup?"
 
(...more cough...)  
 
Sorry,Allen,but I still don't understand your point!:)
 
3/10/2004 4:04 PM
anonymous
... and since each string is plucked at a different time, how can there be only one phase relationship to be concerned about?  
Since the source signal can therefore have a complex phase relationship, how can any of this matter?
 
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