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Old 27th June 2012, 07:42 AM   #1
peter7 is offline peter7  Hong Kong
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Default "pop" noise in relay volume control

My relay volume control have a "pop" noise when i turn it , is it a relay or other problem ? How to fix it ? many thx !!
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Old 27th June 2012, 08:01 AM   #2
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check does you have any DC from preceding or succeeding stage

pics and more info can't harm
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Old 27th June 2012, 09:01 AM   #3
peter7 is offline peter7  Hong Kong
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it can be heard when turn to ten o'clock or four o'clock
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Old 27th June 2012, 11:01 AM   #4
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pics and more info can't harm
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Old 27th June 2012, 12:01 PM   #5
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I agree, it is almost always a small DC voltage on the signal line.
The DC changes with level and causes the pops.
Also known as zipper noise when you rapidly change levels.

It sometimes happens with some steps, not with others, that is because the effect is greatest with greatest steps.
For instance, going from -15dB to -16dB may involve engaging the -16dB relay and disengaging the -8, -4, -2 and -1 dB step relay.

Try to insert a capacitor between the signal and the input to the level control. If the pop is gone, it was the DC. Note that even a few mV can cause this!

jan didden
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Old 27th June 2012, 04:36 PM   #6
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Or firmware change. First turn the relays "OFF" (max attenuation), and then enable the needed relays. This way the maximum "click" will be of the level of current volume setting.

Do you have diodes across relay's coils? There could be back-EMF, ruining the analog signal.
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Old 27th June 2012, 04:45 PM   #7
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Or firmware change. First turn the relays "OFF" (max attenuation), and then enable the needed relays. .
... which will give you two pops. I would attack the cause, clean up the DC on the signal line.
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Old 27th June 2012, 05:35 PM   #8
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If your relays switch to "ON" faster than to "OFF" (given the "ON" increases output), you could get much more pronounced "POP" than two controlled "POP"s at lower volume...
Needs to be checked first to be viable solution, i've seen such solution as the "POP"s fighting method.
This one could be good for "01111111"->"10000000" transition.
Alternatively you can use a binary code without rough "01111111"->"10000000" transitions such as... ehm i forgot his name. The one which for every numeric increment changes just one bit. Then rearrange the relays/resistors to support such binary code.

Gray code, that's his name.
Emm... Is it feasible to implement it with resistive ladders? I am puzzled.
I guess the answer is "No"
Although someone did R2R DAC with it - http://www.google.com/patents?id=DOQ...page&q&f=false
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Last edited by s3tup; 27th June 2012 at 05:44 PM.
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Old 27th June 2012, 05:45 PM   #9
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If your relays switch to "ON" faster than to "OFF" [snip]
Yes, as long as the DC is there. You can change the way you switch a myriad ways until you are blue in the face: as long as there's DC you'll have pops.

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Old 27th June 2012, 06:02 PM   #10
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DACs and their ladders switch DC signal. And their glitches are fine enough to not sound as POPs...

And any analog signal is DC for certain frequency/timebase.
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