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Mesa Plastic Shafted Pots. Why?

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11/23/1999 9:04 AM

Mesa Plastic Shafted Pots. Why?

Feeling kinda stupid here but for some reason I feel I can only replace a pot in my Mesa with one with a plastic shaft. Is this true? I can't think of why this would be a problem but something is nagging me.

I'm either remembering a bad experience from a earlier time with something else or I read this somewhere. I have a pot that will work but it is a metal shaft, and I haven't been able to get into the parts dept. at Mesa to order a replacement.

Thanks

bw

11/23/1999 3:02 PM
gtrboy	i know!!!!! my rhythm 2 gain knob broke on my mark iv and rendered that channel almost useless. piece of crap knob!!!

11/23/1999 4:20 PM

Not sure if this will help nudge your memory. I recently had to replace a pot on a mesa boogie that was previously replaced by a local tech (great tech btw) with a non-original pot (which coincidentally had a metal shaft). The guitarist was complaining that the amp was distorting at lower settings on the pot than it used to. He called mesa, and of course they told him he needed to use the original pot, so he ordered it and had it sent to me. I replaced it with the boogie pot and he was pleased. Apparantly the non-original had a different taper. FWIW

Carlo

11/23/1999 6:12 PM

Yeah, if that log taper pot were replaced with a linear taper, the volume would "come up" a lot sooner for sure.

It doesn't matter in the case of a Mesa amp whether you use a plastic or metal shaft pot, as long as it's the same value and taper as original. An instance where it would be fairly crucial to use a replacement with a plastic shaft would be in a case where the pot had a significant DC voltage across it, like an adjustment pot in a variable power supply. The wiper is already electrically insulated from the shaft in any style of pot, but the extra insulation afforded by a plastic shaft is necessary in some cases.

I like to use metal-shaft pots when replacing broken original pots in Mesas.

11/24/1999 11:01 AM
GFR	When the MarkIV was released I remember that the GP reviewer complained about the plastic shafts (he broke one during the review), and the "manufacturer's response" from MESA was that "due to the high gain of the amp metal shaft pots would introduce static noise".

11/24/1999 12:45 PM

What about introducing hum? I have that problem on the tone pot of my Tele. When I touch the metal tone knob I sometimes get a loud hum unless I ground myself to the strings. I measured it with a meter and found that the knob and pot shaft aren’t always connected to the control plate. I wouldn’t of though it possible that the shaft could pass through the bush without making contact but it is.

Dave

11/24/1999 3:04 PM
BWilliamson	ahhh, I remember that now that you mention it. Maybe that's where I got that idea. I've got a metal shaft I'll give a try and see if I can find a problem with it. Thanks for all the responses bw

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