Mark IV, in Simulclass, loud crackle coming out of standby

[primal]

When I have my Mark IV setup in simulclass mode, when I come out of standby there is a real loud crackle scratch sound. I also noticed a bit of a buzzing or low level hum when in Simulclass as well. It is louder in the lead channel but can still be heard in R1.

In class A it's completely quite. No crackle coming out of standby, no hum. Sounds great.

Anyone else experience this?

 

[Tuna141]

I'd check the power tubes first - the inner pair are the ones that get switched-on when you switch to Simul-class (just the outer tubes are on in Class A mode). I'd try swapping them with a known good pair (providing they are all 6L6's), or try swapping the inner pairs with the outer pair, then running in Class A to see if the crackle follows the tubes.

 

[primal]

Thanks,

So I ran home for lunch and went ahead and swapped the inner output tubes with the outer output tubes like you suggested.

I still only hear the pop/crackle coming out of standby on simulclass. Class A is still silent.

HOWEVER, I can now hear the low level hum on both class A and Simulclass, where before it was only on Simulclass.

Now this is going to be a dumb question, but I will ask anyway.

I have a Road King that has 4 6L6 tubes in it. The Road King runs flawlessly.

Before I go out and drop the cash on the new output tubes, is there any reason I can't pop the tubes out of the Road King and put them into the Mark IV just to see if it fixes the problem?

Thanks

 

[pixy]

Before I go out and drop the cash on the new output tubes, is there any reason I can't pop the tubes out of the Road King and put them into the Mark IV just to see if it fixes the problem?
Thanks

No.

 

[primal]

1 problem down, 1 to go. The hum is now gone.

I still have the loud pop/crackle coming out of Standby when in Simulclass.

I replaced the power tubes with the tubes from my Road King.

Once I come out of Standby and the get the snap crackle pop real quick, it is now perfectly quite. Sounds great, no hum at all.

I spoke with Marcus today at Mesa and he said to try swapping out some of the preamp tubes as they could be getting hit harder by the extra power when in simulclass.

I'm gonna give it a try and see. I guess I can use the preamp tubes from the Road King as well, right?

(Mesa customer suppport is unmatched. I have an 11 year old second hand amp and Marcus took the time to discuss all the different possible causes and even looked up the local repair shopp in my area. Those guys are the best!)

 

[pixy]

I guess I can use the preamp tubes from the Road King as well, right?

right

 

[primal]

I guess I can use the preamp tubes from the Road King as well, right?

right

A man of many words :wink:

 

[primal]

Well, Still have the loud popping crackle when coming out fo standby in simulclass.

New Power tubes got rid of the hum, but not the popping. Swapping out preamp tubes made the popping sound slightly different, but not different enough.

Is it perfectly quite coming out of standby on Simulclass for eveyone else?

I mean, in Class A mode, it is perfectly silent. Not a sound. But when coming out of standby in simulclass, it sort of reminds me of the loud pop you can get at times with the Road King and Roadster when switching from any channel to channel three at low volumes (this seem to be very common on this board). The only difference in the case of the Road King and Roadster is that it is a POP, no staticky crack. With my issue it is staticy

 

[primal]

have you tried different instrument and speaker cables?

it shouldn't be staticy. I had a mark iv and it was generally speaking very quiet (maybe a pop here and there but no crackling, etc)...

The problem occurs doming out of standby without any instrument hooked up.

I haven't tried another speaker cable, I only have one. But I would think if it were a speaker cable, you would hear it more often then just for a brief moment when coming out of standby in simulclass. Plus I think you would hear it in class A as well.

I think I am going to have a tech take a look at it.

 

[primal]

FIXED!!!!!!!!!!!!

Apparently there had been a mod to the Mark III's and Mark IV's where they added two isolation resistors to the simulclass pair of output tubes.

My Mark IV never had the mod. My tech found out about the mod from Mesa, did the mod and now it sounds fine.

So anyone who comes across this thread with a similar problem, get that checked out!

 

[kiff]

what year/rev is your m4? I don't have the problem, but I'm curious...

 

[lawjac]

I just bought my mrk 4, and sometimes get an intermittant crackle in simulclass with standby OFF while im playing. Do you think that mod could be my prob as well??

 

[primal]

what year/rev is your m4? I don't have the problem, but I'm curious...

Sorry, didn't notice when you asked this.

The guy I bought it from said it was bought in 1998.

It is a Mark IVB.

 

[primal]

I just bought my mrk 4, and sometimes get an intermittant crackle in simulclass with standby OFF while im playing. Do you think that mod could be my prob as well??

You would have to ask Mesa, I don't know. There are so many different things that could cause that.

For me it was the moment I switched it from standby to on. It never made the sound after that.

I actually had bad power tubes as well but they were giving me an annoying hum that had this plane lifting off sound to it.