Mark IV loud popping noise when powering down ...

[PuppyPatrol]

First time poster and new member here, so I apologize for asking what may be a previously addressed issue, but my Mark IV makes a very loud popping noise (loudness is dependant on how loud the amp is set as well) when powering down. It seems perfectly normal in all other respects and I've been trouble free with this amp for over 10 years. I never had this problem in my older Mark III which has seen 15 constant years of abused touring throughout the 80s and 90s.

Thanks for any help you can provide!

 

[tim6string]

A Couple of questions. Do you turn Stand-By off first. (that is what I do and there are differing thoughts on this)

Second is the sound a metallic clank or a loud pop?

I get a noticable clank when the preamp tubes are going (getting Microphonic) If you have not changed tubes in 10 years I would definitely suspect tubes.

Otherwise someone else may need to jump in on this.

 

[Boogiebabies]

After 10 years I would perform the following maintenance:

Tool requirements - 1 Chopstick - Do not touch anything with your hands
unless you know how to discharge your filter caps. Hence, the Chopstick.
Put one hand behind your back and keep it in your back pocket. The stick is not made of 98% water, but you are.


1. Visual Inspection of the circuit board - Look for burnt spots
2. Look for leaking yellow goo from the big blue filter caps
3. Clean all switchs internally with De-Oxit or a good contact solvent - Lube with Cai-Lube
4. Clean all pots with De-Oxit and follow with Cai-Lube to re-lube
5. Check the speaker for damage. I use a 9 Volt battery and look for movement.
6. Clean all tube socket pins with De-Oxit and follow with Pro-Gold
7. Power Tubes ( if not fresh)
8. Pre-amp Tubes ( check even if they are new )
9. Have a cup of coffee
10. Smoke a Cigarette
11. Clean input and speaker jacks with contact cleaner and sand.
12. Clean loop jacks. I use 12,000 grit sand paper so they shine.
13. Clean and dust the entire interior and exterior
13.25 Play test. Also try another speaker or cabinet to be sure

****WARNING - THE FOLLOWING IS FOR ADVANCED TECHS ONLY ****
13.5 Check Screen Grid resistors with ohm meter - Blown ones show 0
14. Check negative voltage at pin 5-DOCUMENT -57V
15. Check negative voltage at bias supply caps - DOCUMENT -57V
16. Check Plate Voltage at pin 3 of every PT - DOCUMENT
17. Check Bias with a Bias Meter
18. Ask yourself why you are doing this
19. Re-Assemble and playtest.

Outer sockets may show a lower negative voltage due to Simul-Class
Plate Voltage should be within 1-2 Volts
Bias Meter will determine what % of MPD you are at
Bias supply at supply caps should be equal at -57V
Document any wide variances. And read up on amp maintenance.

This is where I start when I look at an amp. I have been known to Q-Tip for hours and check resistors and capacitors for drift. Some need to be taken out of the circuit to be read, especially when coupled with a resistor.

If you have them, check for two 100 ohm resistors next to each other. They are 50 ohms in paralell. These are for ground reference to the heaters and may hamper the output or buzz. I dont remember if the MK IV has them.

 

[tim6string]

I can certainly do steps 9 and 10. :lol:

 

[Boogiebabies]

Those are the best steps.

 

[fatboy135]

there are two classical ugly sounds on/off switchs.
The first is the due to the classical transitory which exist on the first times on all the circuits there is an overimpulse generate on circuits with caps and coils where they are on a permanent status and we obligate to step into in another status ( for example we force to step from a total discharge off circuit into a 400 volts switch on circuit ), the response of these overimpulse is governet by the topology and values of the circuits. The classical overimpulse is a very short but so powerfull peak transitory.
This issue happens erverytime we try to change the conditions of the amp, for example switching on/off
The second sound is a non classical transitory is like a distorted fart and it becomes on some amps when we power down the amp, these sound becomes from the discharge caps into the powertubes ( as fas as I know )
Neither of these sounds is a fairly trouble to broken anything of your electronics the only point to see is the speaker...

 

[Boogiebabies]

So, in laymen terms, the shock to the circuit upon power up can cause a pop and powering down causes the caps to discharge and tubes to send not only the collapsing signal and collapsing voltage in the output transformer to make a whoopi cushion noise amplified by the speaker.

 

[fatboy135]

that is the super fart :lol:

 

[Boogiebabies]

What a way to put it. All of the EE terminology and it can be broken down to a pop and a fart.

 

[fatboy135]

this fucking fart was the genesis of some tecno songs...

 

[Boogiebabies]

How true.

 

[PuppyPatrol]

Interesting - uhh.. well the popping fart (or farting pop if you prefer) does not happen when powering up, only powering down. It is annoying but if no harm is being done just I just grin and bear it? I've taken it apart and visually inspected and cleaned sockets, etc and it still makes the loud
noise. If it is caused by a discharge could it harm the amp?

 

[Shep]

my mk iv has the light pop when i turn it on...i think thats just the the circut charge..? is that right or do i have a problem...

Also how long do you hav (years) till you have to put in new capictors?

 

[Night0wl1970]

yeah my studio .22+ pops a bit (not all the time) when I turn the standby off. I assume it isn't normal to do this but can it do damage to the amp? I am having it serviced in the next couple of weeks anyway so I will get the tech to check it out.