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Old 29th Nov 2020, 12:16 pm   #1
MurphyNut
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Default Loud pop when turntable switches off

I've recently restored and Bush SRP31D and very pleased with it's performance but its just developed an annoying fault.
After it's finished playing a record and the arm returns to the cradle the turntable automatically switches off and makes quite a loud popping noise from the speaker.
I'm wondering what's causing this and how to sort it out!
Thanks
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Old 29th Nov 2020, 12:19 pm   #2
Michael Maurice
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Default Re: Loud pop when turntable switches off

The cause is likely to be due to the switch contacts arcing. I suggest you add a capacitor of about 10nF across the contacts, or perhaps a suppressor which is usually a C & R in series.
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Old 29th Nov 2020, 12:21 pm   #3
Edward Huggins
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Default Re: Loud pop when turntable switches off

It needs a "switch click suppressor" - in other words a large value (c 0.1uF 500V) cap wired across the motor switch. They used to be standard on some higher end Garrard turntables.
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Old 29th Nov 2020, 7:12 pm   #4
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Default Re: Loud pop when turntable switches off

Thanks very much for the advice, will add the said capacitor tomorrow and report back.
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Old 29th Nov 2020, 10:09 pm   #5
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Default Re: Loud pop when turntable switches off

I think 0.1uF is too big unless it includes a series resistor, thats why I suggested 10nF (0.01uF), make sure its an X rated type, ie 275V AC.
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Old 30th Nov 2020, 1:20 am   #6
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Default Re: Loud pop when turntable switches off

Absolutely agree.

Steve.
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Old 30th Nov 2020, 9:20 am   #7
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Default Re: Loud pop when turntable switches off

Just as an observation I note that 0.1ufd are used in some Bush Radios, without a series resistor.
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Old 30th Nov 2020, 9:53 am   #8
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Default Re: Loud pop when turntable switches off

I have found purpose made snubbers very helpful for this.
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Old 30th Nov 2020, 10:02 am   #9
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Default Re: Loud pop when turntable switches off

Reference my post #7, I was thinking of mains suppression so please ignore my observations, must put brain into gear
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Old 30th Nov 2020, 1:05 pm   #10
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Default Re: Loud pop when turntable switches off

Quote:
Originally Posted by Michael Maurice View Post
I think 0.1uF is too big unless it includes a series resistor, thats why I suggested 10nF (0.01uF), make sure its an X rated type, ie 275V AC.
I've just got back to this before I fitted the capacitor.
I've checked my "stock" and found I have just 1 uF and .22 uF X rated (275V) capacitors, I don't know how critical this is, will either of those do or should I order a 0.01 uF as recommended?
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Old 30th Nov 2020, 3:06 pm   #11
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Default Re: Loud pop when turntable switches off

Much too high. Best order a .01 (10nF) 275V.
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Old 30th Nov 2020, 6:36 pm   #12
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Default Re: Loud pop when turntable switches off

A 0.22uF with 100 ohms in series will be fine.
 
Old 30th Nov 2020, 9:08 pm   #13
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Default Re: Loud pop when turntable switches off

Best thing to do is just try it. Sometimes theory and practice don't always go hand in hand!!
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Old 4th Dec 2020, 1:02 pm   #14
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Default Re: Loud pop when turntable switches off

The first couple of posts suggested the cap is wired across the motor switch contacts. I assume this is in parallel.
Anyway, I've received the correct rated capacitor and wired it in as this and it's sorted out the problem, hardly any noise to worry about now, many thanks for the help
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Old 4th Dec 2020, 1:29 pm   #15
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Default Re: Loud pop when turntable switches off

so what type and value cap did you use.
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Old 4th Dec 2020, 3:06 pm   #16
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Default Re: Loud pop when turntable switches off

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so what type and value cap did you use.

0.01uF, X rated type, 300V
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Old 4th Dec 2020, 5:06 pm   #17
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Default Re: Loud pop when turntable switches off

Question to the boffins - if you have a double pole switch where live cannot be determined (European plugs) then two capacitors should be fitted? Or is it just one for the whole circuit?
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Old 4th Dec 2020, 6:30 pm   #18
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Default Re: Loud pop when turntable switches off

One across each switch, the "liveness" doesn't matter, one will switch first. Which one one never knows. (The first time I have done "one one")
 
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