Boss SD-1 diode changeout

[ronh]

I would like to change out the stock diodes in a Boss SD-1 to the following ones. 1N4002, 1N4148 and 1N36A, I think. A ge type. What order or placement will give me the best sound? Does it matter? Thanks in advance for the help.

[Mark Hammer]

Not familiar with 1N36a, but I gather it is in the same family as a 1n34a.

In a word, Don't. You will not notice any big improvement by doing this, and from the content of your note, it is entirely possible that you might not possess the soldering chops to come away from this with a pedal that works properly the moment you box it up again (apologies if I underestimate your chops).

The SD-1 provides more gain than the TS-9, and employs a 2+1 diode complement to provide something approximating asymmetrical clipping. Replacing any of the diodes with a germanium type will reduce the amount of headroom provided by the existing diode complement. This will result in more intense clipping at lower drive settings, but also lower output volume. That may not be what you want.

What exactly does the pedal NOT do right now that you want/need it to do?

[ronh]

reply

Thanks for your reply Mark. I read a mod somewhere on the internet that said this would be a good thing to do. Its the why I was interested in and your answer has convinced me not to do the mod. It would not be an improvement. Thanks.

[Mark Hammer]

Glad I could be of help. There is something we have collectively summarized over at the DIY Stompbox Forum as B.U.M. Syndrome - the Blind Urge to Mod. It is one thing to take a homebrew design that has not really reached its zenith and find a few things to tweak that make it work better. It is also one thing to take a commercial pedal and adapt it to accomplish a different task or to accommodate a particular circumstance (e.g., what is required to use a pedal with a line-level send/return loop?). But it is a whole other thing to take a pedal that has been systematically developed and refined by a very large development team so as to be palatable to a huge array of users, and decide it is going to be made "better", and that there MUST be a bunch of things you could throw in there to "improve" it. You aren't the first person to ask about mods to a perfectly decent pedal, and the current climate assures you won't be the last.

Sometimes, though, a commercial pedal is fine as is. It happens.

[roseblood11]

Sometimes it´s fine and sometimes it isn´t...

The sound of the stock SD-1 is great, but with a -switchable- GE-Diode you´ll get another great sound for less than $2 - warmer, smoother, more compressed. Search for the Keeley mods...
http://www.robertkeeley.com/product.php?id=13

Some other things to improve: You can replace some of those unbelievable cheap smaller electrolyth caps with film types, panasonic stacked metal film for example...( all values up to 1µF). And you can replace some of the resistors in the signal path with metal film types to reduce noise.

But i think the most important problem of the SD-1 is the following: If you set gain and volume to high levels and switch to bypass you can still hear the distorted signal bleeding into the bypass signal. It´s easy to solve that problem:



But if you´ve done some other mods, there´s a better solution explained here:
http://www.kramerforum.com/forum/sho...d.php?p=258727


Other mods:
http://acapella.harmony-central.com/....php?t=1237455

It´s interesting to solder in a socket and try different IC´s. I chose a Burr Brown OPA2134 in the end. It´s a little bit more hifi now. A NE5532AP works also great (the "A" is important)

But in a way I agree with Mark Hammer: Many mods you find on the web don´t really improve the sound. For example, many people replace caps with different values to get more bass out of that pedal. But that´s not what the SD-1 was made for... It will sound bombastic in your living-room with those mods, but not in a band context. That sharp mid-focussed sound of the stock SD-1 isn´t always beautiful, but it cuts through every mix, where a modded pedal with more bass would just be to muddy... So plan carefully, what you do!

regards, Sue

[Mark Hammer]

I provided a prominent blues player in my town with a modded TS808 that essentially replaced the "3rd diode" with a pot. Increasing the resistance in series with one of the diodes provided continuously variable symmetry/asymmetry, which this player seemed to like a lot. The pedal I sold him replaced his original issue TS-9, which had been stolen or lost. the replacement let him nail a standard TS808 tone, OR, like Sue says, nail something a little different if he wanted.

The trouble with all this diode frenzy is that many players expect the sound to be audibly different from the get-go, when in fact it often isn't. Changeout of diodes often has its most pronounced effect in response to the way you did in with your pick. That provides opportunity for some players, but not for all. In a way, it's a bit like some of the recovery-time mods on compressors; many players simply can't hear what the mod has done because the way they play does not exploit the change very much at all.

I should also say (and I think here Sue might agree with me) that sometimes people get a little nuts with a mod and try to turn a pedal into something completely different. For me, a good mod is something that easily and painlessly opens up new sonic possibilities so that you get two or more pedals for the price of one and a toggle plus a few passive parts, or somethng that lets you fine-tune the pedal so that the quirks of your guitar or amp are compensated for at the pedal in order to get the intended sound.

Case in point. The MXR Distortion+ is an okay pedal but it lacks any tone control. If you normally play clean, and turn the pedal on, there is WAY too much treble. So adding a cap in parallel with the diodes simply lets you use the pedal without having to run to the amp and re-adjust the tone controls just so the pedal won't make your ears bleed and head ache.

[roseblood11]

Yap, agree...

a very simple mod for the SD-1 is to add a toggle to switch from asymmetrical to symmetrical clipping (that´s what the Tubescreamer does). It´s deadly simple and really audible.

Some basic information:
http://users.sa.chariot.net.au/~gmarts/ampovdrv.htm

http://www.geofex.com/Article_Folder...ch/tsxfram.htm

~Sue~

[ronh]

bypass problem fix

I just caught this thread again, I had the bypass problem with my SD-1.
My fix is to replace the 4148 diode that connects to the gate of the bypass FET. New diode, no leakage of signal. Also, if your pedal powers up in effect mode and you dont want it to. Swap the FETs around. My CS-2 pedal did this. Swapped and fixed. As for my SD-1 diodes, left them stock.

[roseblood11]

Hi,

you replaces a 1n4148 with the same type and fixes the bleeding problem?

Can you explain that?

~Sue~

[Mark Hammer]

I've not experienced it personally, since I don't own many Boss pedals, but keep in mind that the diode is the final common pathway of the voltage from the flip-flop circuit. The diode affects what the FET gate "sees". And keep in mind that the FET has plenty more drain-source resistance values other than max and min. So, in some ways it makes perect sense that by replacing one 1N4148 (which does show some quite normal unit-to-unit variation; you can measure 'em yourself) with another, you can go from a switching FET that is aaaaaaaaalmost turned off in bypass mode, to one that is VERY turned off.

The trick, of course, is in knowing what to look for in the to-be-replaced diode and its replacement. That being said, the mere possibility that the often-noted problem could be resolved by replacing a diode (a cheap easily-found two-lead component which is easy to remove) instead of a JFET (harder to find, harder to replace, trickier to identify a "better" one) is very good news indeed.

[defaced]

There is a really cool idea over at the buildyourownclone forum where you can plug in different diodes from outside the pedal. The guy there calls them "Tone Plugs". It may be worth trying.

[ronh]

You said it

Mark, you said it better than I ever could have. This fix worked for me so give it a try. In my 28 years in electronics, I have found a lot of "flakey" 1N4148 diodes. Ron