Starting a Boss SD-1 mod, need advice

[jakeac5253]

So I am learning the fundamentals of electrical properties and how to manipulate audio signal slowly, but I need some reinforcement especially on some of the finer details. I've got some mods in mind and I am just hoping to clear up some things prior to. The mod is to my trusty SD-1 pedal. I want to increase the pedal's low end response, so I should increase the value of certain capacitors, but which ones? Only the ceramic disc caps, or including the electrolytic as well? Only ones placed in series? Only ones placed in parallel? All of them?

Could changing the value of a capacitor damage anything assuming that I solder it correctly and it is placed in the correct orientation if it is polar? I am just wondering if there are certain ones that you don't want to touch.

I am looking at the Erik Hansen site for reference and he says to change C2, C3, and C8, a few other sites seem to recommend the same thing, I was just wondering if there was a way to take this mod to a more extreme level, like if there were other components holding back the low end. I want the tone to be fat city with a nice rolled off soft high end. I know that experimentation is the best way, but that is expensive and time consuming. A few mods have mentioned the coupling caps as setting the frequency response of the pedal. To my knowledge, the coupling caps are the ones in the input section of the pedal directly after the input resistor, correct? Also I have heard that stacking two IC chips improves circuit clarity, how do I do this since there is no designated space for another chip in the board?

Thanks
-Jake

[JoeM]

I think there's some threads on this, you should try a search.

[jakeac5253]

I think there's some threads on this, you should try a search.

Well I did search and did find related topics, but they don't really explain what I am asking. I can find a handful of mods, but I am not looking for a mod, I am looking for an understanding of the circuit and how certain components affect the resulting tone.

Thank you.

[JoeM]

Not the same pedal, but there's some similarity to the Tubescreamer that this should help. Actually I dont think a SD-1 needs modding to sound good.

The Technology of the Tube Screamer

[Mark Hammer]

Pretty common mod. You want to increase C3 from .047uf to at least .1uf and maybe even .22 or .47uf. You can find where the part is here:
http://www.godiksennet.com/images/sch/SD1PG2.JPG

Note that you can "season to taste" by temporarily tacking on parallel caps to the copper/solder side of the board once you have identified where the corresponding pads for the two leads of C3 are. So, adding another .047uf cap in parallel with the existing one gets you .094uf. Adding .1 gets you .147uf and so on. Once you find what value gets you the sort of tone you want, then you can gently remove the .047 cap and replace it with a value that comes closest to your ideal tone.

[JoeM]

Jake,

Do you play in band? I did a similar mod (to increase lows) on a TS clone. Just at home, it didnt seem too bad, but I actually preferred an unmodified one with a group. I'm mainly using guitars with humbuckers, so it may have been a more useful mod with single coil equipped guitars.

You could add a switch to change between values too.

[jakeac5253]

Now that's good advice guys, keep it coming. On my board, C3 is glued to the other components directly adjacent. How do I unglue this, and how do I glue it back afterwards? I have read that leaving those parts unglued may cause feedback howling in the circuit. Is this true?

[jakeac5253]

Jake,

Do you play in band? I did a similar mod (to increase lows) on a TS clone. Just at home, it didnt seem too bad, but I actually preferred an unmodified one with a group. I'm mainly using guitars with humbuckers, so it may have been a more useful mod with single coil equipped guitars.

You could add a switch to change between values too.

I don't play in a band, I play at home and do some recording so I'd like to gain more bass and clear up that fizzy high end. How do I make the switch idea work? Where would I put the other component on the board? Or does it not have to be on the board at all? My guess is a DPDT mini switch with in and out connected to the bottom of the board at the legs of C3 and the mod cap soldered directly to the switch itself so that in one position you get the stock cap and in the other position you get the mod cap, right? That could be wrong though. Seems like it could be done with a SPDT switch as well?

[jakeac5253]

Bump

I really need some info on those glued on components, those are the ones I am going to be changing.

[JoeM]

Did you try Mark Hammer's suggestion of tacking on parallel caps to C3 to find a value you like?

I dont have my SD-1 (I've had 2 - both were stolen), but I dont see how the glue is essential. Maybe you can cut the glue with an exacto knife.

[jakeac5253]

This is what threw me. Read the verbage on the right side.

[JoeM]

Interesting. Maybe Boss had a problem with some caps. The TS clone I use now doesnt have any glue anywhere. I dont think you'll have a problem using good film caps.

[jakeac5253]

Awesome, Joe and Mark I appreciate all the help. I am looking forward to this mod, this is going to be my first actual circuit board mod (I have done point to point modding, and added a small circuit to my Big Muff Pi without changing anything in the active circuit) so any final tips before I dive head first?

[Mark Hammer]

I've had that file for years now, but never stopped to read "the verbiage".

Interesting. Capacitors are essentially two surfaces with an insulating gap between them. You can make a capacitor by simply having two sheets of aluminum foil separated by a piece of wax paper.

Depending on the type and age of the capacitor, and to some extent its physical size, caps can become "microphonic". That is, they can generate tiny fluctuations in signal that eventually start to function like an oscillator., the way that loose windings in a pickup can start generating a signal even when you aren't playing by simply vibrating in place. Whatever insulates the two conductive layers may change its thickness over time, leaving tiny microscopic gaps that permit the interior of the cap to vibrate "freely" in response to taps or loud sound near the pedal (keeping in mind that what counts as "freely" in the world of electrons may well be absolutely invisible to the naked eye).

In the case of the folded-over components, note that: a) they're all caps, b) they're somewhat large compared to non-cap components, and c) they are not only bent over, but are touched several other things. It is not the fact that they are touching other components that is an issue. After all, they are insulated on the outside. Rather, it is the risk/likelihood that the physical contact will be intermittent. In other words, the same components, standing straight up and not leaning against anything, pose no risk of microphonics at all. Tilted over such that any vibration of the pedal from a nearby amp can make those components "buzz"/vibrate against each other ("micro-tapping"), that's when they pose a risk of noise. If they are secured by glue, then that a) holds them in place, and b) dampens any possible vibration.

I haven't seen the guts of any newer SD-1 pedals, but given that cap size has been shrinking over the years since the SD-1 was introduced, but my guess is that the current caps are small enough to stand straight up without touching each other, so the glue is unnecessary....as is the advisory.

Welcome to the world of modding pedals. There is a term it seems I coined, called B.U.M.S., or "Blind urge to mod syndrome". The term refers to the increasing tendency people have to take a perfectly good commercial pedal and change it in some fashion.....simply because they can...and not always for the better. It IS the case that manufacturers like Boss that build their business on selling a LOT of something aim for the lowest common denominator and making the most people happy with their products. That doesn't mean its crap. It just means they want to make as many people happy as possible, so they aim for compromise.

So, it is true that the compromise reached may deliver "less" of something in particular than you want. For example you might want juuuuuust a little more gain, or juuuust a little more treble, or juuuuust a little faster speed. If the pedal is 95% of the way there, and you just need a small component change here or there to make it perfect, then essentially any mods one does are really more like the last lap in the design process. In other words, it's sort of the stuff the design team would have changed over the weekend had they phoned you, but instead they decided on Friday afternoon that the design was a go. Those sorts of mods make perfect sense to me.

Where BUMS takes over is when people want to make bizarre changes that either a) destroy the identity of thepedal or b) turn it into a kind of combination lock whereby you can only get a particular tone (like the stock tone) if you do this, that,that, and set these toggles switches up, and those one's down. In other words, the pedal gets cluttered and unusable in musical situations.

None of this is a slap on the wrists directed at you. Rather, it is a few words of wisdom about how to use your newfound powers for good rather than for evil. As you go about your tinkering, always ask yourself:

• what is it that I *like* about this pedal?
• what is it that I need a little more of in this pedal, and how MUCH more?
• Am I making it too difficult to recapture what made me get the pedal in the first place?
• If I decide I've lost interest in this pedal, have I rendered it unusable for others?
• Is what I added something that will make the pedal something that will continue to hold my interest, and maybe even increase that interest?

There. Now get out there and start soldering!!

[jakeac5253]

Hmm, I am just looking into the inside of my SD-1 and I noticed that the factory has decided to replace R31 and D3 with jumpers, what effect would this have on tone?