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previous: Ryan I I've had several tubes amps and a l... -- 12/12/2000 9:17 PM View Thread

Re: Channel switch popping

12/12/2000 10:20 PM
Re: Channel switch popping
I don't know the specifics of those switching circuits, but I can tell you what basically causes the pop. When you switch, let's say with a SPDT switch, where you are switching between two outputs into a following stage, the key is what are the parasitic voltages resident on/around the switch. Sometimes the popping is caused by a DC voltage offset which resides between what you are switching from, to or between. For example if you are switching between two preamp outputs where one preamp has no DC offset and the other has a couple of millivolts, the couple of millivolts will act as a step function (it can get big if amplified by following stages) to the output and cause an audible pop.  
Another source of popping is caused by the relationship of the switch actuation voltage and its coupling to the output of the switch. Typically there is always some capactitances between the control point on a switch and the switch input/ouput. In the case of a JFET, there are parasitic capacitance between the gate, drain and source of the switch. If you apply a step voltage to the gate to turn on the switch, that step/transient would be coupled to the source/drain and cause an audible pop. The best way to mitigate popping is to:  
a. slow down the control voltage as to soften the transient and make it sub-audible.  
b. remove all dc offsets in the circuits that interface with the switch.  
c. select circuits/switches that have low stray cap.  
I'm sure there are other popping sources I forgot, but this is a start.  
Hope this helps,  

Ryan I Awesome! Thanks for the response!... -- 12/12/2000 10:34 PM