Mark IV combo with SUS-4

[trem]

Hi there,

I just found out that my MIV combo has a SUS-4 sticker on the inside near the speaker. How can you tell whether your Boogie combo is really equipped with a SUS-4? Do all MIV combo come standard with this feature? Thanks.

~trem

 

[mr_fender]

The SUS-4 system basically suspends the chasis by four rubber grommets instead of firmly screwing it down to the cabinet. My '91 Mark IVa combo has SUS-4. On the top of the cabinet it will have four round holes with recessed plastic "cups" (about 1.5" across), one at each corner. At the bottom of these "cups" are the rubber grommets by which the chasis is suspended. Many people think that these were for stacking up cabinets and the feet will interlock into these cups, but they are too small for that and are actually the SUS4 mounts. You can actually move the chasis inside of the cabinet. It feels kind of spongy and not firmly screwed down. It is meant to isolate the chasis from the extreme vibrations of the huge EV speaker in the small cabinet. Neat design if you ask me. Tubes are delicate and need every little bit of cushion they can get.

 

[mr_fender]

To my knowledge, the SUS4 system was used only on the older Mark series amps and has since been abandoned. Newer Mark IV's have standard chasis mounts with the two metal strips on top of the cabinet and no cutouts, just like the heads. I'm not sure when they stopped using SUS4 though. This may be something they changed from the A to B, but don't quote me on that.

 

[trem]

Hey thanks mr. fender. My Mark IV is a 91 too like yours. Yeah, I can feel the chassis wiggling if I push it upwards. The rubber grommets must have a lifespan. Does Mesa sell replacements?

~trem

 

[Russ]

The chassis floats a little in the SUS-4. This is to absorb shock. Mesa probably has some floating around if you really want to replace them.