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Post subject: Is my amp in danger of being damaged???
Posted: Mon Jul 12, 2010 12:17 pm
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Hello all, I'm sure many before me have asked this question, so I apologize for being redundant. But is it dangerous in terms of possibly damaging the amp, to patch Input 1 from the Normal Channel over to Input 2 on the Vibrato channel, while having my guitar plugged in Input 1 on the Vibrato channel side on my silverface Twin Reverb? (I know this is an age old trick to get added boost, but I've never known if it's safe for the amp or not) I'm not sure of the year but I'm pretty sure it is a mid to late 70's Twin. It is the kind that has the master volume that pulls out for added gain. Thanks in advance.


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Posted: Mon Jul 12, 2010 1:45 pm
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It's perfectly safe, sir.

However, certain models of tube Fender reverb combos have the channels wired "out of phase" with one another prior to those signals inputting and summing at V6 (the phase inverter stage). If that's the case then there is little to be gained by patching into both channels since both gain and frequency response are audibly reduced. To eliminate that problem I use a Radial Tonebone A/B/Y footswitch which has a switchable 180-degree phase shift function.

HTH

Arjay

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Posted: Mon Jul 12, 2010 1:53 pm
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So, if my amp IS getting a big boost by doing this patch, then that means it doesn't have this out of phase wiring, and that it's perfectly safe? Correct? I appreciate your response & help by the way.


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Posted: Mon Jul 12, 2010 7:30 pm
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It's technically OK, even if the signals are out of phase. You may not even notice a cancellation until the volume is up over 4- 5. Actually, the vib effect is a function of different phase applications, but it's a controlled type of situation. And you probably know that some guitar pick-up combinations are switchable between in and out of phase selections. If it sounds good to you, then go for it ! Art

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Posted: Mon Jul 12, 2010 7:58 pm
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Fender's opto-isolator "vibrato" has no frequency modulation, Art. It's strictly a oscillated variation of amplitude. Thus, no affect on the signal phase.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Posted: Tue Jul 13, 2010 4:15 pm
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Yeah, I'm with you on that aspect of the signal path, Arjay. The example is a stretch concerning phase manipulation. I guess the phase inverter section would be a better example of this in the signal path. What I was referring to is the how the three RC legs in the oscillator circuit change the phase 60degrees per leg and thus affect the signal. Seems you and I were looking at different sides of the same coin. This amps effect is pretty much a flippn' misnomer, vibrato implies a pitch shift from the original note(a change in the note's frequency). But in reality the change is a time delay,variable frequency(in milliseconds)controlled by the speed pot, and the other two RC legs. Just my view. Art

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Posted: Fri Jul 16, 2010 4:21 pm
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Lazarine, please could you explain that again. I'm easily confused. I'm just trying to work out what is connected where in your scenario. Thanks.[/quote]


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