Why is this switch clicking/poping HELP please - diyAudio
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Old 12th July 2010, 08:55 PM   #1
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Default Why is this switch clicking/poping HELP please

Hi,
I have a severe problem i'm triyng to solve since many days now without succes.
I have build a crossover with a switch section before. Please look at the schematic.
Only switch SW2 makes switching noise only when there is a signal. The more bass in signal the more it cliks. No cliks without signal.
I have tried several solutions but with no succes.
I tried to decouple output of U1 and input of U2, U3, U4, U5.
I tried to put a J111 fet controled by sw2 between R9 and -U3, P3 and R9.
I tried a SSM2412 between U1 - R7, P2 - R9, R9 and -U3.
All of this with no succes. It always cliks with a signal.
What is wrong?
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Old 12th July 2010, 09:34 PM   #2
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If only sw2 is clicking then it sounds most likely a wiring mistake.
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Old 13th July 2010, 12:23 AM   #3
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I doesnt look like a wiring error. Everything is working fine exept this click/pop. Even when I use sw2 only to control the fet or the ssm2412 it clicks but only when there is a signal.
another guess?
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Old 16th July 2010, 08:01 AM   #4
Mooly is online now Mooly  United Kingdom
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Clicks occur because of an abrubt change in DC conditions.
Check the DC output of each opamp output pin under no signal conditions... it must be 0.000volts DC.
What opamps are they ? if bipolar then the change in DC input impedance will cause a click as the bias currents are significant with bipolar devices.

Also you say "the more bass" the more it clicks. It will because you are switching the signal abrubtly at some non defined point in amplitude (seen as a sudden DC shift by the opamp input)... and the lower frequencies are where most of the energy is. There's no way round that with a simple circuit like this.
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Old 22nd July 2010, 11:01 PM   #5
DF96 is offline DF96  England
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sw2 just happens to have more switch bounce/dirty contacts than the others? Are all the switches grounded at exactly the same point?
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Old 24th July 2010, 02:38 PM   #6
Bonsai is offline Bonsai  Taiwan
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Sounds like a DC offset problem to me. Check the wiring around SW2 very carefully.
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Old 24th July 2010, 05:41 PM   #7
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About dc offset it is 0.2mv so this is not the problem.
About dirty contact or loose switch I tried to replace the switch with no succes.
I have build another switch board and the problem on this other board is on SW3, with same click pop noise with signal.
The ground is in star shape and sw2 is the closest to ground connection.
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Old 24th July 2010, 05:50 PM   #8
Mooly is online now Mooly  United Kingdom
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But you say it clicks only when signal present. My reply in post#4 outlines why this happens.
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Old 26th July 2010, 05:21 AM   #9
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Quote:
Originally Posted by Joseph R View Post
All of this with no succes. It always cliks with a signal.
What is wrong?
In point of fact, that's how switches work - they create abrupt changes in level, which sounds bad when music plays. So you have a couple of choices:

a) Wait for a zero crossing of the waveform and only switch at that point
b) Replace the switch by a variable attenuator and ramp up and down slowly

If you search for the solid state volume controls (e.g. Cirrus, Dallas/Maxim, TI) you'll see in their datasheets that they generally implement a) to avoid clicks at volume level changes. I'd say you'd need to implement both a) and b) to make your clicks go away entirely.
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Old 26th July 2010, 09:54 AM   #10
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Mooly is right on this.
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