DOD 250 Diode switch

[tungngruv]

I'd like to be able to switch between LED clipping to the regular diode clipping in my DOD 250 clone. Anyone have any advice or switch (SPDT, DPDT?)diagrams? I remember seeing something like this on a "simple mods" page somewhere. Thanks

[Mark Hammer]

Pretty simple actually, which means you can look forward to things being unlikely to go wrong, which mean you can get back to rocking all the faster.

It would actually be simpler if you had perfboarded the circuit, but I'll assume you used a PCB.

You will need SPDT toggle or slide switch (3 contacts).  If all you can get is a DPDT one (6 contacts), no problem; just ignore the extra contacts (although see below).

Solder the pair of glass diodes to one of the outside terminals of the switch, and solder the pair of LEDs to the other outside terminal.  Since one diode of each pair will go in each direction, just make sure that the two diodes in each set go opposite to each other and you'll be alright.

Once you've done that, take the free ends of all 4 diodes and connect them.  That 4-diode contact now goes to the place where the original two diodes would be in contact with the series resistor and volume pot.  The middle contact of the switch now goes to ground.

Done.

One of the things that happens with a diode change is not only a change in amount of distortion, but a change in volume level.  Switching to LEDs will reduce the amount of clipping produced, but increase the output level.  If you find this a problem, or else wish to keep a constant volume level for some reason, you can use the other set of contacts on a DPDT switch to switch in a series resistor before the volume pot that can reduce the volume bump.  

Wire up a 10k resistor in series with the volume pot (so AFTER the point where the volume pot and diodes would normally meet), and run a wire from each end of the added resistor to the second set of contacts on switch.  One of those wires will go to the middle unused contact, and the other will go to the outside lug on the same side as where your glass diodes are.

What does this do?  When the switch is in the "LED" position, a series resistor is introduced and makes the pot behave as if it is turned down a bit.  When in the other position, the resistor is shunted/bypassed, making the unit behave as normal.  This will yield a tone change without much volume change.  It's not everybody's cup of tea, but if you need it, that's how to do it.  The precise value of the extra resistor may be different, depending on how much volume bump you want or don't want.

[Joe Hart]

Mr. Hammer always with great ideas!

If you wanted to go nuts (space permitting), use a DP6T rotary switch with 6 different diode sets (symetrical and asymetrical) and 6 corresponding resistors! Crazy!

Just a thought!!
-Joe Hart

[tungngruv]

Thanks guys!!!! What a great site where people are willing to help.

[jimbob]

If you wanted to go nuts (space permitting), use a DP6T rotary switch with 6 different diode sets (symetrical and asymetrical) and 6 corresponding resistors! Crazy!

I really like that idea w many diff effects--cool idea. Im actually thinking about buying more of those for more projects! I like the idea of channeling in diff sounds since different amp/and guitars sound diff as well.

[Fret Wire]

The rotary switch works great with Rangemaster caps.

[Joe Hart]

I used the 6-pole rotary idea for switching caps in a wah and it blew my mind! I was able to get 6 totally different sounds out of my wah with a minimum of parts and wiring. And best of all, you aren't introducing lots of different parts to contribute to noise (or possibly suck tone). At any one position (on my wah) I am only replacing one cap with another. Neat!

I'm definitely a big fan of the 6-pole!

And I'm so glad that I could help!!
-Joe Hart

[tungngruv]

First off, thanks to M. Hammer and everyone else who helped answer my newbie questions.  I did perfboard the DOD OD 250 and I did the SPDT switch to go between the 1N914's and the LED's. It worked and both sound great!! My only question is I'm getting a real faint "squeel" behind the notes on the neck single coil pick-up using the LED's. Is that common? I'll mount the effect in a box tonight to see if that helps but we'll see. Once again, thanks to everyone who helped!!!

[Joe Hart]

I don't know about the squeal, but LED's clip at a higher voltage, so you will get more output. Maybe this is causing too high of a signal into your amp? I don't know, but it's a thought. Hope it helps.
-Joe Hart