After trying my hand at the TS808 mods, I thought I'd go for a more general improvement for the SD-1. The Keeley mod dosn't just take the pedal back to another pedal, it improves where the other ones flaw and is my favourite SD-1 mod so far! It uses a germainium transistor as a diode to get a different sound but I found using a plain old NOS germainium diode to be better in tone, I socketed the board so you could swap them out and also experimented with Sillicum diodes which also sounded good - more on that later!

Five Star Mod
You will need:

• 1Uf Capacitor (preferably metal film) x 2
• 0.1uF Capacitor (preferably metal film) x 2
• 2k4 metal film resistor x 1 (red-yellow-orange-gold)
• 620K metal film resistor x 1 (blue-red-orange-gold)
• 47pF capacitor (semi-optional. Sounds just as good without it)
• Germainium Transistor (see below for more options - highly reccomended!)
• Single in line socket, look like this. Used if you want to quickly swap the
  diode config and/or to put the transistor in without damaging it.

Optional:

• Germainium Diode (I used NOS 1N34a ones from small bear. Link)
• Sillicum Diode (I used 1N4148 ones from small bear. Link)
• On/On SPDT switch to swap modes
• You can also use various LEDs in the clipping section, I havn't tried this yet so the results may vary

Replacing Components [Top]

• Remove C10 > replace with 1uF capacitor
• Remove C7 > replace with 1uF capacitor
• Remove R6 > replace with 2.4k resistor (red-yellow-orange-gold)
• Remove R2 > replace with 620k metal film (blue-red-orange-gold)
• Remove C3 > replace with 0.1uF capacitor
• Remove C2 > replace with 0.1uf capacitor

Referance Diagram:

Diode Switching [Top]
There are several options here;

• Germainium Transistor
• Diodes
• Toggle switch

We will start with the germainium transistor. You will first need to have either installed a SIL socket in D6 or have a heat-sink ready to get rid of the heat and avoid breaking the bloody thing! I prefer to use the socket even if you only plan on having one option, it gives the mod more versitility.

You will notice quite obviously that the transistor has three legs, where there are only two holes for a diode. Hmm...buggar! The trick is to use two of the legs in order to make the transistor function as a diode - ask me if I understand how the bloody hell that works! Anyway, on Mr Keeleys site, he says that you need to use the base and emitter if using a PNP the base leg will go to where the black stripe where the diode was and the emitter will go to the other side. If you don't know which legs are which, google the model name of the transistor with the word 'datasheet' after it and it should be easy to find.

The diodes are quite simple. When you look down at the board, you will see diodes D4 and D5 on the right of D6. If you look you can see a black stripe on these diodes. Make sure the black stripe on the sillicum or germainium diode that you use points the same way and insert it into the board.

Switching [Top]
In order to switch between these modes you will need a SPDT switch and a single in line socket if you want to be able to replace the clipping section easily. This is a really cool mod inspired by Beavis audio research's Ultimate Tube screamer when they used a SIL socket attatched to a switch to make swapping and changing easy. I decided to 'borrow' that idea. What you need to do, is wire the left hand side with a SIL socket (you can take the plastic off) and some wire. The middle needs to have two SIL sockets and the right needs one SIL socket and some wire. Like this:


Make sure that the black stripe od the diodes points the right way or the switch won't work.

47pF Capacitor [Top]
On the Keeley site it just says '47pF cap accross the clipping diodes which needless to say made me confused! I finally figured out what he ment when I emailed arround (in otherwords, I asked Berarduur) and he said to put it in parallel with D6. I did it and didn't really notice much difference, it made the pedal slightly smoother, but I used a germainium diode rather than a transistor.

The easiest way to do this is to solder the cap to the bottom of the board, I'll add a referance diagram in the next few days.

To hear clips go to the clip section.

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