Mesa Mark V 25 goes pop...

[pmac11]

Love the range of usable tones I can get out of this little beast. However, the pop it makes when I turn it off - even in standby mode - is not one of them.
What's causing this and how do I eliminate it? Any of you experienced amp techs out there @TV the Wired Turtle @hcsterg @markeebee want to weigh in? Thanks!

 

[pmac11]

Any of you experienced amp techs out there @TV the Wired Turtle @hcsterg @markeebee want to weigh in? Thanks!

 

[TV the Wired Turtle]

Love the range of usable tones I can get out of this little beast. However, the pop it makes when I turn it off - even in standby mode - is not one of them.
What's causing this and how do I eliminate it? Any of you experienced amp techs out there @TV the Wired Turtle @hcsterg @markeebee want to weigh in? Thanks!

before trying to debug anything, if your preamp tubes are over 2yrs old they need to be replaced. power tubes a yr w normal gigging. thats if they are actually good tubes.. first thought is maybe the phase inverter is in the worst shape..
other thoughts: Pop noise can be an indication of a sudden DC voltage shift in the audio path. What typically causes this are coupling caps that are left 'floating' on one side, with the other side sitting at a high DC voltage offset. "Due to the nature of capacitors, what happens over time is the floating side's voltage will tend to rise to match that of the HV side. Then, after engaging another channel or something that connects this HV with an input not at the same potential is goes pop"
ps. did you try this "tip"
amp on standby, watts set at highest setting, cycle through all of the channels on the footswitch. Flip the standby switch, and voila! no more pops?

 

[pmac11]

before trying to debug anything, if your preamp tubes are over 2yrs old they need to be replaced. power tubes a yr w normal gigging. thats if they are actually good tubes.. first thought is maybe the phase inverter is in the worst shape..
other thoughts: Pop noise can be an indication of a sudden DC voltage shift in the audio path. What typically causes this are coupling caps that are left 'floating' on one side, with the other side sitting at a high DC voltage offset. "Due to the nature of capacitors, what happens over time is the floating side's voltage will tend to rise to match that of the HV side. Then, after engaging another channel or something that connects this HV with an input not at the same potential is goes pop"
ps. did you try this "tip"
amp on standby, watts set at highest setting, cycle through all of the channels on the footswitch. Flip the standby switch, and voila! no more pops?

Thanks Tavo!

 

[Bertotti]

Coupling caps are my first thought. I have never just changed tubes because they got to a certain age. I have some going on ten plus years that still sound great. That said that doesn’t mean they aren’t a possibility. I wouldn’t have thought to make that my first guess unless it had been an issue for me before, and it hasn’t. You guys probably fire up amps more often than I do.

 

[Marv666]

I play a Dual Rectifier and read somewhere that the channel switching Pop (for the rectifier atleast) is normal, but there is a way to get it away.
It is while the amp is in standby keep switching through the different channels for a while and At somepoint the Pop is gone.
Don't know about the Mark series but that's my experience with a rectifier

Edit : just read tavo has already written that, ooops

 

[Henry]

I think my express has the similar pop and my vague recollection was that the switching noted above helped. I think I found the switching more bothersome than the pop and just stopped letting it bother me.

 

[Ricochet]

Even Solid-States pop.

 

[Bertotti]

Better a pop than a whisper! My TX dI’d that to me once. Turned it on let it warm up hit a chord and a split second of chord then a whisper. Four new power tubes aren’t cheap.

 

[hcsterg]

@pmac11 : does it pops exactly when you activate PWR and/or SBY switches, or is there a delay, even small ?

A pop often reveals a poorly conceived switching, even if made with VTL optoisolators - hence my question above.

A+!

 

[stiv]

Even Solid-States pop.

My Standel pops twice. When you switch it on/off and when the 120v-220v transformer switches off.

 

[pmac11]

@pmac11 : does it pops exactly when you activate PWR and/or SBY switches, or is there a delay, even small ?

A pop often reveals a poorly conceived switching, even if made with VTL optoisolators - hence my question above.

A+!

It pops when I turn off the main power, regardless of whether it's in standby or not.

 

[hcsterg]

It pops when I turn off the main power, regardless of whether it's in standby or not.

OK - I think that the chassis of your Mk V 25 should look like this one below, that I saw fo servicing :



I would do this quite easy following test - be careful @pmac11, it involves MAINS connection :

A - put the chassis on your bench (stably, on shims) like I did on the pic above.
B - connect the mains, the speaker cab.
C - power the amp : is there still the POP in the speaker ?
D - now do 2-3 ON/OFF powering successively and quite quickly : do you have POPS ? Lower ? Louder ? And at each back and farth switching or not ?
E - power off and unplug the amp.
F - search in your components drawers a 0.1µF 1000VDC or 1500VDC (OK : if you have a good condition 600VDC, it will be OK for the test only).
G - connect accross the terminals of the POWER switch that capacitor (by any means, as long as it is safe and correct, OK ?).
H - retry C and D steps above : is there still any POPS heard in the speaker ? Nearly unchanged or neatly attenuated ?

A+!

 

[pmac11]

OK - I think that the chassis of your Mk V 25 should look like this one below, that I saw fo servicing :

View attachment 203513

I would do this quite easy following test - be careful @pmac11, it involves MAINS connection :

A - put the chassis on your bench (stably, on shims) like I did on the pic above.
B - connect the mains, the speaker cab.
C - power the amp : is there still the POP in the speaker ?
D - now do 2-3 ON/OFF powering successively and quite quickly : do you have POPS ? Lower ? Louder ? And at each back and farth switching or not ?
E - power off and unplug the amp.
F - search in your components drawers a 0.1µF 1000VDC or 1500VDC (OK : if you have a good condition 600VDC, it will be OK for the test only).
G - connect accross the terminals of the POWER switch that capacitor (by any means, as long as it is safe and correct, OK ?).
H - retry C and D steps above : is there still any POPS heard in the speaker ? Nearly unchanged or neatly attenuated ?

A+!

Thanks. I will try that!