Switching Noise

rnbboy@comcast.net · 01-18-2007, 04:35 AM

I have a problem with a SPDT switch that is used to switch two different caps in and out of a cathode circuit. The problem is that the switch "pops" through the speakers when the switch is first used. After the first time, the switch is quiet and the popping noise is gone. Anyone know what might be causing this and/or a cure for the problem as I don't want to ruin any speakers prematurely. Thanks in advance for any help with this matter.

stokes · 01-18-2007, 05:03 AM

It is just the cap charging up,wont hurt anything,I believe it can be quieted by putting a low value resistor in series between the cap and ground,the exact value I am not sure of,maybe someone who has done this recently will chime in.The idea is to slow down the cap charging with a small resistance.It wont hurt your speaker though.

Steve Conner · 01-18-2007, 11:59 AM

To get rid of the pop, you need to pre-charge every unused capacitor to the same voltage that it'll want to settle to when it gets switched into the circuit.

Generally, that means shunting a high value resistor across each pair of switch contacts, so while they are sitting open, a little DC can trickle through the resistor to charge the cap up.

In a tube cathode circuit, I think 100k is enough to count as "high". I've used 10M for this purpose in grid circuits, but this would be too much to charge the large electrolytic caps used in cathode circuits.

Enzo · 01-19-2007, 10:37 PM

100k works fine. But 1 meg also works fine. Just allow the caps to be charged.

01-18-2007, 04:35 AM	#1
rnbboy@comcast.net Junior Member Join Date: Sep 2006 Posts: 3	Switching Noise I have a problem with a SPDT switch that is used to switch two different caps in and out of a cathode circuit. The problem is that the switch "pops" through the speakers when the switch is first used. After the first time, the switch is quiet and the popping noise is gone. Anyone know what might be causing this and/or a cure for the problem as I don't want to ruin any speakers prematurely. Thanks in advance for any help with this matter.

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01-18-2007, 05:03 AM	#2
stokes Old Timer Join Date: May 2006 Location: NYC Posts: 1,305	It is just the cap charging up,wont hurt anything,I believe it can be quieted by putting a low value resistor in series between the cap and ground,the exact value I am not sure of,maybe someone who has done this recently will chime in.The idea is to slow down the cap charging with a small resistance.It wont hurt your speaker though.

01-18-2007, 11:59 AM	#3
Steve Conner Supporting Member Join Date: May 2006 Location: Glasgow, Scotland Posts: 2,985	To get rid of the pop, you need to pre-charge every unused capacitor to the same voltage that it'll want to settle to when it gets switched into the circuit. Generally, that means shunting a high value resistor across each pair of switch contacts, so while they are sitting open, a little DC can trickle through the resistor to charge the cap up. In a tube cathode circuit, I think 100k is enough to count as "high". I've used 10M for this purpose in grid circuits, but this would be too much to charge the large electrolytic caps used in cathode circuits.

01-19-2007, 10:37 PM	#4
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,303	100k works fine. But 1 meg also works fine. Just allow the caps to be charged.

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