MXR Pedal Foam

[Audiotrove]

As I continue to go through my old vintage pedals to clean them and make sure they are in good order, I've got a question about old MXR pedal foam. I have several vintage MXR pedals and need to clean the crumbling gunk off of them. I know this has been covered before but I'm looking for the latest thoughts on the best material to replace the old MXR foam. Thanks for any input.

[Mark Hammer]

Yu can buy sheets of what is often called "Fun Foam" in hobby/crafts stores.  From a distance, it can be easily confused with the felt squares those same stores often sell.  It's not as spongy as what MXR originally used, but it holds up better, and you can easily cut it with scissors.  I also like it for how it can stop protruding ends of leads on the copper side from shorting out against the chassis.  It also comes in lots of colours if you have an inclination to match the foam with the chassis colour!

[willienillie]

I see red paint, is that an old Dyna Comp?  When you get it cleaned up, do you mind telling us what transistors are in it?

[Audiotrove]

It's a circa 1979/1980 Dyna Comp.  I'll do one better, I'll post photos.  Probably get to it this weekend.  I've got too many irons in the fire.  Working on a Mu-Tron III, a Vox V846, a Boss OC-2, an ADA MP-1, and the Dyna Comp.  That's just the first batch of projects.

[willienillie]

I always read online about a mix of MPS5172 and 2SC1849, at least for the older script logo Dyna Comps.  But in all the pictures they are face down, so I've never been able to verify.  In my clone I have an MPS5172 for Q1, and 2SC1849s for the rest, and they aren't coming out.  The '1849s are fairly low gain, say 150-ish, and for whatever reason they really brightened up the tone compared to when I had higher-gain '5172s (250-ish) in all 5 spots.  Not harsh bright, but "proper chicken pickin" bright, if that makes any sense.

[Rob Strand]

I like the idea of plastic sheets, like Boss use.   They last forever.

[bluebunny]

I've used thin Neoprene sheets in a couple of builds (from craft suppliers), but mostly I'm with Rob: bits of plastic sheet, cut to size and scored.  Seems to be a ready supply of the stuff from some landfill-friendly vendors (*cough* Hercules *cough*).

[skyled]

I was a polyurethane chemist for 5 years and I can tell you that unless foam is very dense it's basically junk in the long (or even short) run. It either falls apart into a messy powder or falls apart into a sticky goo. Nearly all Hammond tonewheel organs built after 1963 will be destroyed by a disintegrating and corrosive foam that Hammond put in them because it's very difficult to clean out and few people know about it. Certain Moog synthesizers have a similar problem.

I would say stick to tried and true insulation materials like felt, hard plastic, and fishpaper.

[Kipper4]

I've used thin Neoprene sheets in a couple of builds (from craft suppliers), but mostly I'm with Rob: bits of plastic sheet, cut to size and scored.  Seems to be a ready supply of the stuff from some landfill-friendly vendors (*cough* Hercules *cough*).

I've been using the craft EVA foam for a while. Doing my bit to save the planet.

[Audiotrove]

I always read online about a mix of MPS5172 and 2SC1849, at least for the older script logo Dyna Comps.  But in all the pictures they are face down, so I've never been able to verify.  In my clone I have an MPS5172 for Q1, and 2SC1849s for the rest, and they aren't coming out.  The '1849s are fairly low gain, say 150-ish, and for whatever reason they really brightened up the tone compared to when I had higher-gain '5172s (250-ish) in all 5 spots.  Not harsh bright, but "proper chicken pickin" bright, if that makes any sense.

So the CTS pot codes on this Dyna Comp are 1378029, which puts this pedal as mid to late 1980.  Just about exactly 40 years old.  The opamp is a National Semiconductor LM3080N.  Had to scrub the gunk off it with a toothbrush and CRC cleaner to read it.  Messy and time consuming job to clean it carefully.

I wish I could help you out with the transistors.  I gently lifted one up from the board to take a high resolution pic of the front, but there's no number on it.  The transistors appear to be all the same.  Here's some pre-op and post-op photos.  Happy to say after putting it all back together it still works.  There's a reason these were popular. 

I was thinking about selling little baggies of "Vintage MXR Foam Dust" to sprinkle into your pedals for extra mojo, but I decided to just get rid of it.

[Audiotrove]

I was a polyurethane chemist for 5 years and I can tell you that unless foam is very dense it's basically junk in the long (or even short) run. It either falls apart into a messy powder or falls apart into a sticky goo. Nearly all Hammond tonewheel organs built after 1963 will be destroyed by a disintegrating and corrosive foam that Hammond put in them because it's very difficult to clean out and few people know about it. Certain Moog synthesizers have a similar problem.

I would say stick to tried and true insulation materials like felt, hard plastic, and fishpaper.

The good news is now that I've thoroughly cleaned it, it will be quite easy to change out the temporary fix I used to get it back together.  Thanks for this.

[willienillie]

I wish I could help you out with the transistors.  I gently lifted one up from the board to take a high resolution pic of the front, but there's no number on it.  The transistors appear to be all the same.

Hey, thanks for the effort.  And good job on the cleanup.  I've seen pics with those "flat" looking transistors in Dynas from that period, but I guess we won't know what they are.  I'm surprised the chip is socketed, there's very little room vertically in those.  I would guess maybe they were having issues with 3080s (noise?), and wanted to be able to swap them out easily at the factory.

[Audiotrove]

There's almost no clearance with the opamp in the socket to the back of the case.  Forced me to use very thin foam.  The upside is I can switch opamps whenever I feel like it.

[moosapotamus]

These have worked well for me...

[amptramp]

I was a polyurethane chemist for 5 years and I can tell you that unless foam is very dense it's basically junk in the long (or even short) run. It either falls apart into a messy powder or falls apart into a sticky goo. Nearly all Hammond tonewheel organs built after 1963 will be destroyed by a disintegrating and corrosive foam that Hammond put in them because it's very difficult to clean out and few people know about it. Certain Moog synthesizers have a similar problem.

I would say stick to tried and true insulation materials like felt, hard plastic, and fishpaper.

But MXR foam is going to be the mojo part that you use to keep bumblebee capacitors from shorting to the chassis.  Extra points for using it as the footpad on a wah pedal.