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phase shift oscillator LFO?


 
12/21/2005 9:56 PM
markphaser phase shift oscillator LFO?
The Fender tremolo used a phase shift oscillator why is that?  
 
What does the phase shift oscillator output look like?  
 
Whats the LDR LFO is it a phase shift oscillator?  
 
Why use a phase shift oscillator LFO for the tremolo circuit?
 
12/21/2005 10:23 PM
Enzo

What other form of LFO might you suggest? It is a perfectly simple circuit, a single triode with the plate signal looped back to the grid via some RC delay. The output ought to be more or less a sine wave.  
 
"Whats the LDR LFO"  
 
What do you mean? The trem circuit is two parts. First there is an LFO to make the trem signal. Second there is some sort of interface to take the LFO signal and connect it to the audio path. You can use an LDR in series or in shunt across the signal path, or you can use the bias yanker method. And other ways exist. But the LFO is essentially independent of the interface.  
 
Why use it? WHy not?
 
12/21/2005 10:50 PM
markphaser
Thanks for the help  
 
is the LFO output a triangle or sine wave?  
 
The LFO for the bias methode used what kind of LFO a phase shift oscillator and why?  
 
The LDR used a LFO that was not a phase shift oscillator but what kind of LFO?  
 
"a single triode with the plate signal looped back to the grid via some RC delay"  
 
How was this done?
 
12/22/2005 12:39 AM
MatthiasM

http://aikenamps.com/PhaseShiftOscillators.html
 
12/22/2005 5:16 PM
markphaser
I still don't get why a phase shift oscillator is different than a regular oscillator?  
 
It has phase shift network in the feedback loop of the oscillator which changes the frequency  
But what is different about the output and speed pot when changes its frequency does it "Shift" the triangle or sinewave output or something whats so different about the phase shift network?
 
12/22/2005 5:41 PM
Enzo

What specific circuits are you looking at? You are drawing distinctions that I don't see. Take a gain stage, and add feedback, and you have an oscillator. Other than the phase shifting kind, what other form of LFO do you see out there? A phase shift oscillator IS a regular oscillator. RF oscillators might use a tank circuit, but that is not very useful at LFO frequencies, and a crystal osc would be pointless. There are variations on the circuits of course. You can even wire up a multivibrator circuit - a flip flop - but that takes two triodes instead of one. The basic PS osc is simple reliable, what else do we neeed?  
 
It doesn't matter what you connect it to. The oscillator's job is simply to make a low frequency signal. You can connect that signal to a light bulb that shines on a photo-resistor, or you can conect that signal to the bias supply, or wherever yuo want.  
 
You are asking what is different about a phase shift network, but you don't tell us different from what?
 
12/22/2005 8:04 PM
markphaser
A phase shift oscillator has phase shift in the feedback loop  
 
A regular oscillator is just a gain with a feedback path thats all (No phase shift network in the feedback loop)  
 
I was just wondering what does the phase shift network do in the feeback loop that is different than a normal regular oscillator ?  
 
A regular LFO oscillator ( with out phase shift network in the feedback loop) VS a LFO phase shift oscillator? What does the output waveform do thats different between these 2 designs?
 
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