whats up with mark iv channel switching pops?

[willrock]

hey guys, i have had this problem since i got my MarkIV about 4 years ago now, im just tolerating it but i think i better do something with it. This loud pop only happens when switching channel from dirty to clean, but it never happen when switching from clean to dirty.. anyone on the same boat with me here? any fixes for this?

 

[thindave]

What are you using to switch channels - an external device or the built in footswitch? If it's an external device, chances are it's a ground issue. I had the issue when trying to use the G-system's two relays to switch between the 3 channels - when using 1 relay, it was fine, but as soon as you tried to go between the two, you would get the pop.

See this post:


http://forum.grailtone.com/viewtopic.php?t=13317

 

[HalfDeaf]

I have this problem with my mkiv A using the standard FU-3 footswitch. It seems to be worse when the total lead gain (gain+drive) is high and the R1 gain is low. I have found that if I turn the R1 gain high enough, and run the lead channel with almost no total gain, there switching pop goes away. I don't have any fixes - my amp tech (Mesa certified actually) told me he could mess with the guts of the footswitch and fix it, but I have seen the schematics and I have my doubts. The switching system is VERY complicated (relative to traditional tube amp designs). If somebody has a real fix, I'm all ears.

One more thing - on my amp, it seems much less noticeable at higher volumes.

 

[bryan_kilco]

mine does not pop with footswitch, but does seem to make a pop when using the dial on the back of the amp.

 

[Tyrant]

My FU-3 footswitch recently developed some switching issues as well. It will randomly stay in Lead/EQ no matter what is switch is pressed. It'***** or miss as to reliability.

Anyhow, I've also recently noticed that when switching from lead or R2 to R1 it will give a quick loud sound as well. It seems that it depends on how hard you hit the strings before you switch. Has anybody else noticed this?

The cable part# is- CBL.FU3/MS and costs $61.75

Before I dump 70 bucks I thought I would chime in here and see if anyone had any ideas first.

 

[ketiov]

I've got the same issue as the thread starter. There's a pop when switching from Lead to Rhythm 1. Doesn't happen anywhere else. I do have the original footswitch.

 

[willrock]

i have this problem both using the footswitch or an external switch. im gona call mesa

 

[jvk]

There's a relay, Rhy1, which is switched on for R2/Lead but is off when R1 is enganged, it's purpose is to drop the level of signal going to the poweramp. Beside this relay, the rest of the switching in the MarkIV circuits are performed with noiseless LDRs, and it appears that Mesa used a relay here to save the expense in using 2 separate LDRs, along with transistors and rest of components required to switch them. The solution or a potential mod is to use a small circuit to replace the relay with 2 LDRs.

Logically, using the footswitch or the amp to switch channels is electronically identical (the footswitch turns on the same parts of the switching circuit that the pulls do) so pops will occur either way.

I'd be interested to know Mesa has to say on this.

 

[kbourque]

Any more info on this? Mine does this occasionally.

 

[Monsta-Tone]

I noticed that the switch made the popping noise on both of the Mark IV's that I had and the Roadster that I used to have, where the footswitch didn't.

 

[zebpedersen]

My Mark IV B does this too. It's not a constant problem and it's never been massively loud, but it is a little irritating.

If there's an easy fix I'd love to hear about it, but the Mark IV's switching is mighty complex...

 

[willrock]

i called mesa last week and i talked to Marcus. He said that unfortunately thats is the imperfection of all MARK IVs. The external switching system and the manual channel selector knob at the back shares the same circuit that obviously pops. However, the footswitch has a different circuit the eliminates pops. anyways, i retubed my mark IV and i got rid of the pops and of course using the footswitch.. so just expect the **** POPS if your using an external switching system!

 

[trem]

i called mesa last week and i talked to Marcus. He said that unfortunately thats is the imperfection of all MARK IVs. The external switching system and the manual channel selector knob at the back shares the same circuit that obviously pops. However, the footswitch has a different circuit the eliminates pops. anyways, i retubed my mark IV and i got rid of the pops and of course using the footswitch.. so just expect the **** POPS if your using an external switching system!

Good info. You should link or maybe copy this into the Mark IV thread.

 

[kbourque]

I have this problem with my mkiv A using the standard FU-3 footswitch. It seems to be worse when the total lead gain (gain+drive) is high and the R1 gain is low. I have found that if I turn the R1 gain high enough, and run the lead channel with almost no total gain, there switching pop goes away.

This is pretty much how mine is. It doesn't matter how high I have any settings on Rhy2 or Lead but if I put the Rhy1 gain on 9-10 then it completely goes away. Seems the lower I have the gain on Rhy1 the more it tends to pop when switching to it.

Wonder if mine could be a pre-amp tube or if it's just the way the amp works. Mine's only a couple of months old.

Kris

 

[thindave]

You need to use an external unit to switch channels via midi - like the cfx-4 - since I believe the switches on the MkIV share a ground (I think that's what I was told long ago). Once you use the cfx-4, you're problems will be over...