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cathode bypass switching pop supressor

12/14/2005 9:23 PM
cathode bypass switching pop supressor
I have a switching arrangement on a preamp I am working on that combines a 10k and about another 10k and .68, I am getting a loud pop I know there is a way to put like a 100k or so to keep from getting the pop just confused about how that  
was drawn I think KOC had it covered in one of his books.. any examples would be great thanks  
12/14/2005 10:28 PM
Don Symes

I have 2 ideas that may help.  
Idea 1 - use an LDR/Vactrol as the switching element - that should provide a 'soft' switch.  
Idea 2 - Instead of switching in a parallel element, put them in series and use your switch to short one of them. That may mean buying a pair of 5-ish-K resistors instead of 2 10k's. (You don't mention your switching topology.)  
Pops are generally the result of having DC build up on one of the switching contacts, but a relay without a coil flyback cap or diode will be very likely to pop.  
Hope this helps!
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12/16/2005 1:05 PM

I am kinda doing the series method I am using center off switches with ground in the center  
a full 10k to the cathode to ground  
one 5k6 across the switch in series with the other  
5k6 which has the .68 to the top of the other 5k6 is tied to the cathode and one end of the switch its really a cool setup  
because you can go from the unbypassked 10k, to about 5k partial bypass all the way down to about 3k5 with the .68 semi partial bypass I guess.  
I was thinking maybe 1 meg from the switch poles to the center off, I know a drawing would help...  
it works great you get a wide range of gain from one stage just the pop thing..  
12/16/2005 4:17 PM
Chris/CMW amps

Hi Steve  
By going from 10k to 5k or the other way around you do change the biasing from that stage so it will pop anyway whatever way of switching is used 'cause it does take a some time for the tube-stage to re-adjust.  
12/16/2005 6:18 PM
Steve A.

Chris said:  
By going from 10k to 5k or the other way around you do change the biasing from that stage so it will pop anyway whatever way of switching is used 'cause it does take a some time for the tube-stage to re-adjust.  
    Exactly what I noticed in my experiments with the Pignose G40V! Only it seemed like the point where the noise occurred was around 2K7 (that could depend on the voltage and current of the preamp stage).  
    I even tried wiring the cathode up to a 10k pot to see if I could avoid the popping noise, but I got a "whooshing" noise around 2K7.  
    However if you avoid crossing that particular threshold, switching the cathode resistors can be fairly quiet.  
Steve Ahola
12/17/2005 6:31 AM
Put a large value resistor, 100K to 1M, in series with your cap. To switch the cap in, short the large value resistor. No DC change, no pop.
12/17/2005 2:40 PM

Thanks guys I will experiment a bit  
I think in series with the cap is the way I did see it drawn
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