Loud pop when switching on or off, any cure?

Discussion in 'Amp Central Station' started by Blue Bill, Mar 20, 2017.

  1. PCollen

    PCollen Friend of Leo's

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    I can't reach that site , but I think the 220K, 1W resistors you are referring to may be balance/bleed resistors across the capacitors at the first, B+, power supply rail feed. In the schematic I included on my post, these form a 50/50 voltage divider to ensure that the voltage is evenly distributed across the upper (C12) and lower (C13) capacitors, and also provide a path for the B+ voltage to drain off those caps when the amp is turned off and not remain stored, which could give someone a real surprise if they opened up that amp and got across that voltage by accident.
     
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  2. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    Hi PC, thanks again for the help. Rob's diagram for the surge resistor shows a 220K resistor jumpered directly across the standby switch:



    Standby Switch 'Pop Reduction' and Current Surge Protection
    One modification I highly recommend on amps with Standby Switches is placing a Surge Resistor across the Standby Switch terminals. It will quiet or eliminate the Standby Switch 'pop' by allowing a small current to flow around the Standby Switch to charge the Filter Capacitors. This prevents an inrush current surge when you close the Standby Switch. It also helps control the fly-back voltage spike from a choke when the Standby Switch is opened.

    With this resistor in place you should place the Standby Switch is in the standby position before powering up the amp. Turn on the Power Switch then wait around 15 seconds for the tube heaters to come up to temp and for the pop resistor to charge the filter caps enough to prevent a current inrush which is what causes the switch pop. Preventing current inrush should also make your filter caps last longer.

    I like to use a 220k 1watt Surge Resistor. Adding the resistor eliminated all Standby Switch pop from my 5E3 amp.

    [​IMG]
     
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  3. seekir

    seekir Tele-Holic

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    Blue Bill:
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  4. BobbyZ

    BobbyZ Doctor of Teleocity

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    The cap you guys are talking about looks sorta like a. . . . .like a . . . ....................... DEATH CAP . . . .
    (insert horror movie music here)

    Actually there's a proper name for those things, I just forget what it is now.
    Nothing really to add, just stirring the pot. :)
     
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  5. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    You spooked me a little. I think the death cap is on the front side of the power transformer, on the 120V line; this one is fed off the secondary, behind the rectifier diodes, so if it shorts, the chassis would be powered up with 400VDC; sounds dangerous. But then, there's about 14 other caps between this voltage and the chassis ground, so maybe it's not likely to cause trouble. :eek:
     
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  6. BobbyZ

    BobbyZ Doctor of Teleocity

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    You're right Bill the "death cap" is on the ac line.
     
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  7. PCollen

    PCollen Friend of Leo's

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    If you can provide one single named brand schematic that uses this resistor for this purpose, I might give it some further thought
     
  8. Bandito

    Bandito TDPRI Member

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    I came in to a Campion 110 with the same problem. I put a snubber 1uf 630v poly cap in series with a 100ohm 3w metal film res across the power xfrm primarys. Worked great.
     
  9. jimash

    jimash Friend of Leo's

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    My Mesa Subway Blues makes a loud pop going into standby.
    It changes depending on the volume level and what is in V1.
    Turning it down before turning it iff is probably the best way not too hear it.
     
  10. Cherygo

    Cherygo NEW MEMBER!

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    Here was the easy and inexpensive fix for the loud pop when I turn off my Fender Frontman 25R:

    Turning down the volume on either or both the amp and guitar had no effect in eliminating the loud pop which occurs only when I TURN OFF the amp and it has no standby switch.

    My routine is to simply turn on the amp and play, then before I turn the amp off, I plug in the headphones (or you can use an inexpensive headphone jack adapter only in the input jack, no actual headphones needed). Turn off the amp and NO POP!!!! Simply unplug the headphones or jack adapter after the amp is off, and you're ready to jam the next time you turn the amp on.
     
    Last edited: May 27, 2021
  11. milburn

    milburn TDPRI Member

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    Oh man, i'll have to try this as my Frontman 25R has done this forever ( bought new in 1998 )
    Ill post back up to let everyone know if it works on mine too.
     
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  12. Dadzmad

    Dadzmad TDPRI Member

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    Thanks for the tips with the Champion 110 mine pops loudly when turned off - late night low volume beauty that pops and wakes em up when done.
     
  13. Geo

    Geo Poster Extraordinaire

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    My Champion 20 does the loud pop also. I put a jack in the headphone plug and that mutes it some.
    I get it on a Blues Junior also, quite noticeable but not real loud. If I touch my thumb on the
    plastic handle while finger is turning off the switch though it won't do it. Think in this case
    it is static buildup.
    None of my point to point older Fender or others have this issue.
     
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