Micky's Big Blog

Modding a BOSS CS-3 Compression/Sustainer

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Here we go again. This time with a BOSS pedal I rescued from the sands of time...
This was a beat-to-death CS-3 Compression/Sustainer. It suffered mostly from cosmetic damage, but a lot of what was wrong was due to neglect. It didn't 'look' too bad but when I opened it up it was obvious that someone took this thing, tried it and then threw it in a box somewhere and forgot it.

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As you can see, it is a little beat on the outside, but opening the battery cover revealed why this pedal was sold to me so inexpensively. It looked like the battery had been installed in the pedal since the 80's when it was purchased, and then someone forgot about it. Took me a good amount of time to pry the battery out, and quite a bit of corrosion was left to clean up.

A trick my dad showed me a long time ago was to mix up a slurry of baking soda and water, then use a cotton swab to stop the corrosion from doing further damage and clean up the area a bit. I tried to find a date on what was left of the pedal, but that was an exercise in futility... The grommet that BOSS uses to pad the battery cover screw was pretty much toast, but there was enough there for me to leave it until I can order a replacement from Small Bear Electronics. I have found they are the least expensive place I could find for many BOSS replacement parts. If you know of a better place, please comment on this blog below and let me (and everyone else) know.

I thought the battery connector was gonna be fried, but it was surprisingly clean for the amount of corrosion on the battery. I installed a fresh battery into the pedal, plugged a 1/4 inch TS plug into the output and the pedal turned on and off as it should. Good news! Here is the spec sheet from the Service Notes:

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Since it seemed to turn on, I thought I would try it connected to an amp and guitar. It turned out to be a good 'before' snapshot of the pedal, since I basically knew what I wanted to do before I even opened it up. No mind you, I don't really have a 'need' for the CS-3, I already own a DigiTech Main Squeeze, which is basically the same thing. I don't use that one much, but I thought I might try it and see if I could learn a few lead guitar parts and use the sustain and compression to cover up my sloppy style. Turns out, it only amplifies my sloppiness, but I can play enough to learn the weaknesses of the pedal and over time, compare it with the DigiTech.

The pedal worked, the pots were scratchy and the sustain seemed to be very subtle. On the gain channel on my DSL it seemed to work much better, but what I was really looking for was a Carlos Santana type of screaming clean that I haven't really been able to master. Oh well...

Opening the bottom of the pedal revealed another reason I got the pedal so cheap, one of the AC adaptor wires was making intermittent contact, and when I touched it, it broke off completely. But the main board itself was very clean, and appeared to have no previous modifications. Here is a photo before I modified it:

Unmodified BOSS CS-3 main PC board

One of the things you might notice right away is the clusterfu@& between R1 and R3. Those are the 2 electrolytics I would end up keeping (but replacing with new), all the other ones I replaced with 1uf tantalum caps. I could have used non-polarized caps, but I am a big fan of tantalums, for their accuracy as well as their stability. All of the silver poly caps you see will be replaced with dipped monolythic ceramic caps, as anything has got to be better than the crap BOSS uses for these things.

Here is the schematic in case anyone wanted it:

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One of the first things I look for when modding a pedal is the components used for the build, most notably the 'quality' of the components chosen. You can tell BOSS has a very sound design here, but they kinda 'cheaped out' when they went to assemble it. For example, using the op-amps they did was a very good design, but surrounding the op-amp with lesser quality components doesn't help at all. For example using cheap electrolytic caps and flimsy poly non-polarized junk on the op-amps inputs and outputs allows for a higher noise floor and can introduce spurious (unwanted) harmonics that can make a tone sound harsh and sterile. Maybe that is what they were looking for, I dunno, but to me those are the first two things I look at when anyalyzing a pedal like this. Here is the solder side of the board, not very useful unless you can read the components backwards. I have enough reading them normally...

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Since this blog only allows me to embed 5 objects per post, I will have to continue the mods in the next entry. Hopefully on future posts the limit can be raised. Anyway, the plan is to replace all the caps on this board, as well as a few resistors. Unfortunately all I have for metal film resistors is 1-watt or 2-watt, so they will have to be soldered in standing up. No worries as there is plenty of room for the ones I wanna replace. The 1N34 diodes I plan to use will fit perfectly, as well as all the caps. Almost all of the components I have on hand, except for a couple planned op-amp changes.

When I first looked at the board and saw 8-pin inline op amps, I kinda got worried. As far as replacements go, there aren't a lot to choose from. In this case, the M5218AL Mitsubishi op-amps installed on the board are only OK, there are just a couple alternatives I would like to try, the JRC5532 is almost always my go-to chip in these pedals, and the NJM4558 is the only other I might try. I have a 4558 already, but I will need to order more 5532's in a SIP package.

One of the tasks I absolutely dread is unsoldering chips from boards. If I am gonna do a section of a board with SMT components I will almost always use a hot air rework station, but in this case SIP removal will require a bit of Solder-Wick and a delicate ESD pencil. Lately I have been using enough Solder-Wick to warrant the BIG spool, about $12 each off Amazon. I like how the come vacuum-packed, in order for the flux not to oxidize.

I am only going to remove the first two op-amps, IC1 & IC2. Looking at the schematic IC1 deals with the input 1st gain stage and the power dropping section, and IC2 deals with the tone and the 2nd gain stage connected to the sustain circuitry. The plan is to install inline sockets, so that experimenting with different op-amps at a later stage will be much easier. I didn't really want to mess around with DIP to SIP adapters such as those you can buy on the Monte Allums' site as it would have allowed me a much greater selection of op-amps, such as the OPA line. SIP op-amps are much more limited in their selection. Besides, there are only two that I would have wanted to try here anyway. It is just I have to wait for the 5532's to come from China...

A more in-depth circuit analysis is found here, a forum thread from 2012 that I found very interesting...

Updated 07-24-2020 at 09:27 AM by Micky

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  1. Micky's Avatar
    In the next photo you can see the inline SIP-8 sockets installed, as well as the components I have replaced:

    I still have a few resistors left to replace, mostly in an effort to reduce the hiss this pedal can generate. I only have a few metal film resistors, and I am trying to keep the cost of modding this pedal low. I have yet to look thru the cabinet for the last few that I need. You can see the 1W that I used, they are the blue ones installed on-end in the above photo.

    One area I would like to point out is in the top left, where the glob of glue sat on top of the 3 caps. Here you can see I replaced the electrolytics, and replaced the silver non-polarized cap. Much neater if I do say so myself. I have replaced 3 other diodes (1N34, you can see them with the black bands). The machined sockets seem to be the most reliable, especially with several insertion cycles.