caps& resistors role in vibrato circuit &nb

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tubenit
Junior tube assistant
Posts: 54
(3/31/04 4:41 pm)
 caps& resistors role in vibrato circuit
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 I am wondering what role resistors (and caps) play in a vibrato (tremolo) circuit. For example: In a circuit you might have a 1M resistor prior to a .01 cap "coupled" to another 1M resistor to a .01 cap "coupled" to a .02 cap going to a 3M pot & 100K resistor (such as on a Princeton Reverb). I discovered that changing one of the.01 caps to a .02 cap seemed to either deepen or slow the vibrato (in a way that I like). What do the resistors do and if I changed one to a higher (such as a 1M to a 1.5M or 2.2m) or lower value how would that impact the sound. Thanks for ALL the info and help - it helps! tubenit
 
tubenit
Junior tube assistant
Posts: 55
(4/1/04 8:10 am)
 Re: caps& resistors role in vibrato circuit
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 Going back and reviewing schematics of 3 amps I am familiar with, it appears that the higher "speed" vibratos have higher resistor values. Would it be accurate to assume that this thinking would be headed the right direction? For example if I replace a 560K resistor with a 1 M that the vibrato speed would increase (or deepen?). Any feedback would be appreciated. Thanks!
 
zachsdad
Posts: 5
(4/1/04 10:02 am)
 Phase Shift Oscillator
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 Below is a simple description of a phase shift oscillator and the resistor/capacitors I believe you are referring too. Notice that changing the component values change the amount of lead/lag and therefore the frequency of oscillation. This is an excerpt from "Electronic Principles (Second edition p.537) by Albert Paul Malvino" You can probably find it in any college library if you want to research more.

Leslie

Edited by: zachsdad at: 4/1/04 10:09 am
 
tubenit
Junior tube assistant
Posts: 56
(4/1/04 5:27 pm)
 Re: Phase Shift Oscillator
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 Thanks for the resource and the help! tubenit
 
Tiny Daddy
I will work on all amps
Posts: 586
(4/1/04 7:38 pm)
 Re: Phase Shift Oscillator
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 Thinking of this another way, what you have is a multi-section low-pass filter that provides a 90 degree (or more)phase shift. The amplifier (tube) provides another 180 degrees of phase shift plus gain. So when the input is connected to the output the circuit oscillates at the
filter's -3dB point which is where the filter's phase shift occurs.
 
 
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