At 26:44 in this video of Johnson's 1984 Guitar Institute of Technology (GIT) clinic, Johnson answers a student's inquiry about his equipment:

Basically, what it is is I use three different systems. I use the Twin through the Stereo Chorus which is screwing up, but... I use that on the two channels with a little bit of reverb and I use the Stereo Chorus and Echoplex, and then I have an A/B that switches over to one of the channels only in the Twin, over there next to the Marshall, that I have the reverb in the second channel tapped over to that so I get a little o' that... and that's, I set that on like ten, and use a Fresh Fuzz, and that gives it this kind of little bit of, kind of a dirtier rhythm sound. And then the Marshall—it's kind of a three-way setup—and then the Marshall goes to the reel, the reel kinda.

The "dirtier rhythm sound" is demonstrated at 27:47.

The Fresh Fuzz is mentioned again in an interview with Electromagnets and in an interview about Seven Worlds, which record that Johnson had a Fresh Fuzz during that period. In both interviews, Johnson is not sure if he used it in the studio.

Electromagnets interview

Did you use Hi-Watts on the album?

ERIC: Yeah, I used a Hi-Watt 100 head though a Marshall cabinet. And I used an early-'70s Marshall 100-watt head through a Marshall cabinet. And an Echoplex, probably the Fresh Fuzz. I used either Bill Maddox's '57 Strat, and I used my 335. Oh, and then I used a 1960 Les Paul Standard on Salem through a 100-watt Boogie head through a Marshall cabinet.

Is this the same gear that was used in the Electromagnets video?

ERIC: That's that same Les Paul through a Boogie head and a 4x12 cabinet.

Seven Worlds interview

Effectwise, I think I used a Tychobrae flanger and the Fresh Fuzz and the Echoplex.

For live shows with Boston, Delp used a Fresh Fuzz modified by bandmate Tom Scholz, as mentioned by Scholz in an August 1977 Guitar Player interview. The interview was transcribed by rockman-gearup.com user REO Speedweasel on October 3, 2016.

The only other piece of modified equipment that Boston uses onstage is a fuzz box run between singer Bradley Delp's Gibson L6-S electric guitar and Ampeg V-4 bass amp head. "I think the thing is called a 'Fresh Fuzz'," says Tom. "It's a cheap little box that I traded for a six-pack a while ago. I put in a few resistors and capacitors to boost the high end and give it a shelf. You get more raunch than fuzz out of it now, which isn't bad at all!"