Popping sound

Hammeron

When I switch the JCM 900 off it makes a loud popping/echo sound.
Stanby on wait a few minutes and put power on.
Power off then standby off. Is this the correct procedure ? Is the sound normal ?

VellaJ

Power your amp off in the reverse order of powering it on.

Therefore, when turning off, your full power switch should be the last thing you touch...

Hammeron

VellaJ wrote: Power your amp off in the reverse order of powering it on.

Therefore, when turning off, your full power switch should be the last thing you touch...

Ok great. Still makes the sound tho....

teleplayer

For powering up a tube amp, it's best to let it warm up 1st.

I turn my power switch on, then go put my pedal board down, tune up, etc. Then turn my amp on.
This way i'm not waiting around for it. If i'm all setup and the amp is just off, I give the amp 3 mins or so.

Same for power down, I turn the standby off, pack up all my cables and guitars, then power off. (3mins or so too)
You also have to remember to let your amp cool before moving it around too violently.

Proper care of your valve amp will make a huge difference in the life of the valves.

You may still get a popping sound, this is not unusual, maybe try turn your master volume down before turning on or off if it's really bad.

VellaJ

On my amp I've found the popping sound to be exaggerated if I turn off while the crunch is still on.

+1 for leaving it on standby before turning completely off. This allows the valves to cool somewhat (with a little current running through them) before the final cooling of total power-down.

Is the popping sound when switching your Standby switch or you Main Power switch?

shaunf

I read somewhere that putting the amp into standby first before powering off leaves the caps charged up and so you should actually not do this but rather just power it off with the volume pots down and then switch the standby switch to off. The amp will make a whooshing noise sometimes accompanied by a thump. In any case powering off with the standby off or on won't hurt the amp but charged caps could be dangerous to someone working on the amp even if it has been unplugged for some time.

Gearhead

Standby mode is for woessies. There are as many arguments for using it as there are for not using. It has more to do with the coating applied to the cathode than with temperature; forget 'cooling down', the tubes don't get all that hot anyway.

Never mind thump, you do more with a ham fisted palm mute. The one thing you could try to figure out is whether there is less thump if you switch off pedals first, or what happens if you turn the volume down first or whatever you can think of.

AlanRatcliffe

Gearhead wrote: Standby mode is for woessies.

And those of us with SS rectifiers ? But you don't have to worry about standby when turning an amp off anyway...

The one thing you could try to figure out is whether there is less thump if you switch off pedals first, or what happens if you turn the volume down first or whatever you can think of.

shaunf wrote: charged caps could be dangerous to someone working on the amp even if it has been unplugged for some time.

I don't think it makes a difference to cap charge if standby is on or off.

...And anyone who doesn't discharge the caps as a matter of course before working on an amp has no business poking around inside a valve amp anyway.

ezietsman

Alan Ratcliffe wrote:
I don't think it makes a difference to cap charge if standby is on or off.

...And anyone who doesn't discharge the caps as a matter of course before working on an amp has no business poking around inside a valve amp anyway.

My amp discharges the caps when the standby is off (like when I'm playing) when I turn the power off.

+1 on the expert working on the amp, they'll know how to make the danger go away, the careless ones will only be careless for a short while...

shaunf

Alan Ratcliffe wrote:
Gearhead wrote: Standby mode is for woessies.
And those of us with SS rectifiers ? But you don't have to worry about standby when turning an amp off anyway...

The one thing you could try to figure out is whether there is less thump if you switch off pedals first, or what happens if you turn the volume down first or whatever you can think of.
+1

shaunf wrote: charged caps could be dangerous to someone working on the amp even if it has been unplugged for some time.
I don't think it makes a difference to cap charge if standby is on or off.

...And anyone who doesn't discharge the caps as a matter of course before working on an amp has no business poking around inside a valve amp anyway.

For sure. And I'm one of those who has no business poking around inside a valve amp! Was just regurgitating what I heard a well known amp tech say in a Youtube video, and it wasn't necessarily as a safety mechanism, but rather just that if you do power straight off, the caps discharge, which is why you continue to hear a noise after you hit the switch, as opposed to if you switch to standby first before powering off.

Gearhead

Also only very partly true, since he current through the tube is dependent on the heater supplying free electrons. The heater power supply is going to fall away immediately on the average guitar amp since it usually is AC. So any sound still coming out of your amp will be the remaining free electrons flowing into the HV caps, which will not empty those caps to the point that you want to touch them.

Luke-JvR

hmmm Interesting one…

Firstly I have to ask, did your amp do this before i.e. the popping sound? If not then did you change something on the amp or maybe in your rig, use an attenuator?

So what I would try is, use amp as normal then engage standby and turn off all volume and gain and see if it still pops. If it does, something is up and it sounds like it is discharging so some component might have been damaged. I would take it in or get a tech to check it as messing around with this yourself if you are not sure what you are doing could worsen matters.

Good luck and hope you get it sorted.