Loud pop when switching on or off, any cure?

[Blue Bill]

A fellow I got to play with yesterday asked if anyone knew what the story is with amps that have that loud pop when switched on or off. He said he has a Fender Super(something), red-knob, solid state amp; he just picked up a pedal steel and wants to use it for that.

I've had amps that do this, and heard many others. Is there a typical cause for this? Thanks!

 

[Milspec]

Is the volume / master at zero when he turns it on? Instrument plugged in? Volume on guitar down?

None of my amps pop like that unless I have the volumes turned up when turned on, but if that isn't the case, I would suspect the input jack.

 

[tap4154]

I had a SS Champion 30 that popped like that. Called Fender and they said that's just what they do. Just turn the volume down when turning on and off. Later got a Frontman 25R, basically the same circuit, but no pop. Seems they built in some kind of bleed resister/cap/circuit that stopped it. In fact when I turn it off the OD light comes on, then fades. The Champion didn't do that.

 

[PCollen]

Here's the fix. Capacitor C4 , .047uF to ground , right before the standby switch in the attached schematic. Doesn't matter what type of rectification you have, or whether or not you have a standby switch, that's the fix. Of course, just having the volume on zero when turning on/off is a much simpler solution to implement.

 

[Blue Bill]

Is the volume / master at zero when he turns it on? Instrument plugged in? Volume on guitar down?

None of my amps pop like that unless I have the volumes turned up when turned on, but if that isn't the case, I would suspect the input jack.

Excellent questions, I'll ask him next time we play, next Sunday.

Input jack? Like a dirty or loose connection?

I had a SS Champion 30 that popped like that. Called Fender and they said that's just what they do. Just turn the volume down when turning on and off. Later got a Frontman 25R, basically the same circuit, but no pop. Seems they built in some kind of bleed resister/cap/circuit that stopped it. In fact when I turn it off the OD light comes on, then fades. The Champion didn't do that.

Thanks Tap.

Here's the fix. Capacitor C4 , .047uF to ground , right before the standby switch in the attached schematic. Doesn't matter what type of rectification you have, that's the fix.


View attachment 413580

Thanks PC. I guessed that a cap would be the solution, but wasn't sure where it should go. Do you know what sort of voltage is at that point? I assume it it around 400 V, or something like that. I have a bunch of .047 caps, I'll see if any are high voltage rated.

 

[Obsessed]

KISS. Turn amp volume all the way down before turning it on or off.

 

[skippolony]

My Marshal MG 15 practice amp gives a loud pop when switched
on or off even with the volume/ gain all the way down.

 

[RubyRae]

My Pro Reverb does this, and I always have volume on 0.
It's not crazy loud, but I am always twitching when I go to turn it off.

Sucks really...

 

[Grant Austin]

I've got the same issue with my DRRI. Volumes at 0 and POP!

 

[seekir]

I have two Peavey Bravos, one I bought new in '93, and one I bought at a pawnshop a few years ago. The first gives a "shoop-pop" when I turn it off (not on), but the pawnshop Bravo is dead quiet and makes no shut-down noise. I always put them on the clean channel and zero the volume before turning them off. This has no apparent effect on the noise the first amp makes, which really isn't bothersome to me. It's been doing it since it was new, hopefully it isn't harmful to the amp.

 

[Blue Bill]

I have a '73 DR, over the years it has sometimes popped on or off; these days, it's nice and quiet. Kinda mysterious. I did find a handful of 630volt .047 caps, so perhaps I'll install one in my friend's amp and see if it works.

Seekir - how's life in Hilo? I lived over on Kauai for a few years, I love to visit the Big Island.

 

[mherrcat]

I have a Peavey Nashville 400 that I use for pedal steel and it has that same issue; can't remember though whether it occurs when turning on or off because I haven't used it in a while. I do remember, though, that I could minimize the pop by turning the reverb control all the way down. Odd.

 

[Pup Tentacle]

Surge resistor. Rob Robinette has a write up here; https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Pop_Reduction

 

[Blue Bill]

Surge resistor. Rob Robinette has a write up here; https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Pop_Reduction

Wow, I've never been to his website, it is Packed with mods! Thanks for the tip. So, either a shunt .047 cap or a 220KΩ-1W jumper resistor, or...both?

 

[Frodebro]

I've got the same issue with my DRRI. Volumes at 0 and POP!

Mine pops if I flip the standby off when it's powered up, but flipping the power switch first solves that problem.

 

[Greenstreet]

Yup. The surge resistor worked on my Pathfinder.

 

[Grant Austin]

Mine pops if I flip the standby off when it's powered up, but flipping the power switch first solves that problem.

That is almost certainly my issue. I always put it into standby before turning off the power. Woops.

 

[Frodebro]

That is almost certainly my issue. I always put it into standby before turning off the power. Woops.

I flip the standby first on all my other amps when powering them down, but not the DRRI. 'Cause it freaking pops.

 

[Ira7]

It's a common thing on some Fenders. My SS Champion 110 pops at an annoyingly horrible volume 10, even if the vol is set to ZER0.

The fix?

Stick a jack in the headphones input if you've got one when turning off. Doesn't even need to be connected to a cable.

 

[PCollen]

Thanks PC. I guessed that a cap would be the solution, but wasn't sure where it should go. Do you know what sort of voltage is at that point? I assume it it around 400 V, or something like that. I have a bunch of .047 caps, I'll see if any are high voltage rated.

You want 600-650 V in that position. The schematic I showed used a radial polyester (like a Mallory 150) rated at 600V. It has to handle voltage from the rectifier driving the power supply rail. The rectifier in that amp puts out about 450-475V, so 600V is good for that application.