Turntables thump when turning off?


Why?  I have used 4 different tables and three phono stages in 2 different systems and all of them produce a pretty loud thump when turning off especially, sometimes when turning on.  I have been muting the system each time I turn off as it seems a little much to be letting such a thump reach the speakers.  Is there a cure?  lift grounds?  arrange cables? I was getting a pretty decent hum at times and I've noticed careful routing of the cable to the phono preamp makes a huge difference in this.  

61a8fc83 0497 4515 996b c2556036d4eaejlif

You can try a spark suppressor across the switch terminals.

0.1uF 600V film cap in series with a 250R 1 watt resistor should work. 

Turn mute on or volume all the way down, whenever you turn stuff on or off or switch inputs. If thump is not loud you will be OK. 

I have been muting the system each time I turn off

You already figured it out.

What turntable? More than one brand or type? When you say “off”, do you mean power off or just platter motor off?

You solved the concern with muting. Relax and enjoy the long weekend and listen to your stereo.

The thump is loud, very loud if it's at the full volume I would play an LP at.  I guess you guys are saying it's normal and I just have to live with.  It's there no matter the table or phono stage and even does basically the same thing in a whole different system.  It's a VPI classic 3 and Rega RP8.  I had Nottinghams before and those don't turn off ever so maybe that is why I didn't ever notice until now.  You have to stop the VPI motor after every LP side since it uses the center weight and periphery ring.  The RP8 I can just snag the LP off without stopping it.  

"The thump is loud, very loud if it's at the full volume"

You know what the Doctor says to patient?

It hurts when I do "x" Doctor-then don't do "x"

 

Contact VPI.  Some of their turntables had an issue with making a pop when powered off.  They sent me a capacitor for free for my Classic 2 and it was a pretty easy fix and resolved the issue.

Ground the motor.

Try the above suggestions, you can do it.

Hard to imagine that a snubber cap across the power switch would be missing or broken. But I would definitely check.

More distance between turntable power switch and phono pre might already be the solution. Is the power cable to the turntable very close/parallel to the interconnects from the cartridge to the phone-pre? After all the snubber only minimizes the problem and doesn't neutralize it totally.

If nothing works and you are really “desperate” you can build in an extra switch that only turns off the low voltage connection to the motor. You would lose the warranty but the problem would be fixed. But I would first try disconnecting the motor manually (unplug the cable if possible) instead of using the switch and see if the problem is gone.

Well known issue with VPI and Rega tables. A cap across the power switch of the right value is the answer. I had that issue years ago when I owned a Rega. 

.01uF HV ceramic cap across the switch.

.01uF HV ceramic cap across the switch.

+1 @lewm 

@ejlif 

This is a common problem- if the 0.01uf 1000v disk cap across the switch fails, it will result in a thump or pop no matter where that switch is in the system and it will show up more on the phono preamp.

Its caused by the magnetic field of the motor or power transformer collapsing and causing an enormous high voltage spike (the same principle that energizes spark plugs in a car BTW). This is picked up by the phono section because it has the most gain. The cap shorts out the high frequencies that are otherwise jumping across the switch contact as its opened. For this reason it also prevents the switch from being damaged- the switch contacts erode a bit every time this happens.

So you do want to get this fixed rather than use the mute!

You know what the Doctor says to patient?

It hurts when I do "x" Doctor-then don't do "x"

 

Yeah no sheet.  I was looking for a solution to having to turn down the volume or mute each time I change the record.  Just pointing out that if left at normal volume that I play a record at the thump is dang loud.  Obviously I don't do that and I turn it down.  

Sounds like plenty of suggestions.  I was thinking it's probably not a fault of one of the tables.  I have a VPI classic 3, a Rega RP 8 that is brand new and an old Dunlop Systemdek IIX and they all do it and with two different phono preamps and various amps and preamps.  I'll try some of the more careful wire routing see if that helps.  Thanks for the many useful suggestions.  

I was thinking it's probably not a fault of one of the tables.  I have a VPI classic 3, a Rega RP 8 that is brand new and an old Dunlop Systemdek IIX and they all do it and with two different phono preamps and various amps and preamps.

Now that's an interesting bit of information! And that causes me to think its not a failed power switch bypass cap. You have something more basic. I would investigate your AC wiring- have an electrician test the outlet to see if its properly grounded and the AC wiring is correct. This could also be caused by an unshielded tonearm cable being routed very near the  turntable power supply, but this latter idea is a bit sketchy.

Best practice is change the input or mute every time. If you think that's a hassle, maybe after you call the electrician, re-wire your house, and six weeks later still have the same problem, you will have a shall we say somewhat different perspective on that?