Mark iv fx loop mod

[prm2770]

I have searched the forums for the specifics of this mod and haven't found it. The reason I ask is that my FX loop SUCKS. I am very new to using it I must admit but when you click it on from the footswitch it makes a god awful noise and it doesnt blend well...as in the volume is considerably lower. I have to Crank my fx to get them level but then they clip. So either im really stupid or my fx loop is bad. Any comments? What are the details of this mod? I have a couple mesa authorized repair shops in Dallas/Fort Worth that can do the work im sure but I really value your knowledge before I contact them.

Thanks,
Phill

 

[Fronzil]

the fx loop on my IV is great..I can't tell any difference when its on, just going guitar > amp, or through my pedal board...i only run my carbon copy, and soon my analogman modded DMM...but the CC sounds great..very clear, no noise whatsoever..couldn't be happier.

 

[kiff]

bad preamp tube maybe? according to the manual V2 is the fx return.

 

[prm2770]

hmmm good to know. I have a new set already on order. I have never changed the pre amp tubes...my new 12ax7eh's should be here any time, hopefully that will fix it!

 

[GD_NC]

I was having similar problems with my Mark IV loop. The culprit in my case was bad LDRs. You probably need to take it to a Mesa tech.

 

[prm2770]

forgive my lack of tech terminology...LDR?

Phill

 

[kiff]

light dependent resistor.

 

[prm2770]

ok, light dependant resistor...got it.

I had some spare preamp tubes behind the face plate. So today I swapped some preamp tubes around to see if that helped and bingo FX loop works fine, i think. I need to test some other units to make sure that the noise is from the effects processor that I used today, there is a slight hum on the lead channel. Turns out that in V4 was a 12at7 and eh12ax7's in V2 and V3. In V5 was some Marshall tube that had no identifying #s on it. I didn't uncap V1 but I will tomorrow. But the crackling oh the crackling on power up. I have a whole new set of ax7s on order so hopefully that will quiet the noise.

Now about this LDR business. Someone mind explaining what it is and what it does?

Thanks!
Phill

 

[emperor_black]

Maintain a balance between the channel volume and o/p volume. Somewhere in the manual I read the channel volume serves as a SEND level?

 

[kiff]

ok, light dependant resistor...got it. Now about this LDR business. Someone mind explaining what it is and what it does?

:lol:

It basically acts as a switch. I think the reason they use them, instead of relays, is that they don't pop from a sudden contact being made... as a relay can.

Maintain a balance between the channel volume and o/p volume. Somewhere in the manual I read the channel volume serves as a SEND level?

the channel volumes do indeed affect the send level.

 

[prm2770]

Wow, I've read the manual cover to cover and didn't catch that one. Guess I'll go read it again. O/P? Output? If so how can you possibly do that? At anything above like 2 that would be so loud as to be unusable. Maybe I'm confused.

Phill

 

[emperor_black]

Wow, I've read the manual cover to cover and didn't catch that one. Guess I'll go read it again. O/P? Output? If so how can you possibly do that? At anything above like 2 that would be so loud as to be unusable. Maybe I'm confused.

Phill

yeah, sorry, o/p is output or the master volume. I'm not in a band anymore and at home, I'm running tweed, master at 3 and preamp volumes at 2 or 3 depending on if wife's complaining too much that day or not. :lol: Its not loud at all. I usually run the master at 4 or 5 and preamp volume at 4.