How would you fix this popping power switch?

[semitone]

I just completed a 5E3-like amp*

The power switch makes an annoying pop (through the speaker) on power-off. There's no standby switch, I left it out.

My guess as an advanced novice is that there is either arcing in the switch, or that the filter caps are discharging audibly.

I have seen schematics where a 220k/1w resistor is in parallel with the first filter cap(s). Would doing this help?

My other thought is to use a STDP switch for power instead of an STSP.

Or am I completely off?

Thanks very much!

*My "5E3" uses Hammond 272DX and 1620 trans, putting 325 plate VDC and 35 mA on JJ 6V6S tubes. It sounds awesome!

[Tom Phillips]

I agree that there is probably arcing in the switch. Some equipment uses an arc suppression circuit across the switch contacts but that is usually not required on a small guitar amp power switch. If it were me, I’d try an upgrade to a better quality switch. SPST should be fine. A double pole switch configuration won’t help unless it’s just a better switch.

The 220k/1w resistors you have seen across the first stage filter caps is for a different purpose. They equalize the voltage across caps in series.


Regards,
Tom

[guitician]

It could be the input picking up the EMI from power off. Is the input floating with a high impedance?

[semitone]

It could be the input picking up the EMI from power off. Is the input floating with a high impedance?

I'm afraid I'm not far enough along... electromagnetic interference is it? There are a couple of 100w bulbs on about 16" away from the chassis... would that do it?

Also, I use a floating trem with hot pickups, if that's any help

The switch is a Carling, but it's seen a lot of heat over the years (!) so I'll get a new one.

Thanks,

semi

[Gtr_tech]

A film cap across the pwr switch terminals will help suppress arcing when the contacts open up. This was a common technique in older pinball machines that used high power flipper/end of stroke switches with tungsten contacts to extend the life of the switch.

[semitone]

A film cap across the pwr switch terminals will help suppress arcing when the contacts open up.

Tech, can you suggest a value and voltage rating?

[guitician]

Is the guitar plugged into the amp when this happens? If you unplug the guitar from the amp and the amps input circuit is not grounded by the jack itself, then the amp can pickup all sorts of noises.

[Gtr_tech]

Tech, can you suggest a value and voltage rating?

Value isn't really critical...anything between say .01 and .05 should be just fine. Get the highest voltage rating you can find. I'd go for 600-630v rated 'cause that's a DC voltage rating, not AC.

[semitone]

Thank you, the capacitor across the power switch stops the pop.

There's buzzing, but there's a lot of old solder... and it's not a Carlling, but an offshore value selection.

Thanks to all who responded!

semi

[semitone]

Oh, one other thing, about buzzing. And this really should be on any debugging page....


Is your soldering iron off? semi

[guitician]

On Fender amps I've always seen those caps put on either side of the primary to ground, or on the pole of a SPDT switch labeled "Ground". I guess that served the same purpose(noise suppression), but was only energized when the amp was on, they removed power from the cap with the power switch open and the amp off.

[Enzo]

Guitician, that cap does a very different job. That is the famous "death cap." The grounding cap references the chassis to one side or the other of the mains. This is done to provide some hum abatement in two-wire mains systems. This has nothing to do with power switch popping. it is best replaced with a three-wire mains cord.

The cap Gtr tech refers to is across the power switch contacts, not from switch to chassis. Turning the switch ON wuold effectively short across his cap. When you turn off the power, it is normal for a switch to arc a little. It takes a second or two for the power to drain from an amp, so the electrical noise from the arcing switch can be picked up and amplified by the amp's circuits. You hear it as a pop.

Wiring a cap across the switch contacts greatly reduces contact sparking. Thus it reduces popping at power down.

[guitician]

Yeah, I've been shocked by a lot of those leaky old (Death)caps, but nothing really biting like touching the line voltage itself. Some Fenders with three prong cords have a .047 125 VAC cap on the neutral side to ground, I guess that kept it safe. My amp just has it on the output of the rectifier before the standby switch and serves the same purpose of suppressing spikes in the power. If the power transformer has a copper band, it eliminates the need for suppression caps.

Oh, and I wasn't saying to put a ground cap in, just that they used to use them like that.

[AllAmpedUp]

I agree that there is probably arcing in the switch. Some equipment uses an arc suppression circuit across the switch contacts but that is usually not required on a small guitar amp power switch. If it were me, I’d try an upgrade to a better quality switch. SPST should be fine. A double pole switch configuration won’t help unless it’s just a better switch. The 220k/1w resistors you have seen across the first stage filter caps is for a different purpose. They equalize the voltage across caps in series.

Hey everyone, I am just digging about for answers...related to my on/off popping issue (Fender Princeton 112+)
I will re-read this tread and try to understand the install of that extra cap.

BUT....am I reading the post correctly.....Will replacing the power on/off witch with a new one actually (potentially) solve the problem?

[AllAmpedUp]

sorry for re-post...
Hey everyone, I am just digging about for answers...related to my on/off popping issue (Fender Princeton 112+)
I will re-read this tread and try to understand the install of that extra cap.

BUT....am I reading the post correctly.....Will replacing the power on/off witch with a new one actually (potentially) solve the problem?