HOW?

This from the Stomp Box forum here at TDPRI:

"the ts pedals always come to mind when we talk of smooth ODs. ive always wanted a ts but the only one i could find is the ts-5 with the plastic shell. the mids are good for some, to me its ok. what i did was to make a boss sd-1 into symmetric clipping like a ts by adding a diode to the stock 3. the stock boss sd-1 is assymmetric which has a rougher grittier sound. now the sd-1 has a smooth od i am looking for. its my longest standing mod on a pedal. my mods on the ds-1 on the other hand are always changing."

How would I go about accomplishing this?

what exactly want you to accomplish??

SD-1 to TS9?

I'm not asking anything like that. Literally what I mean is how is this mod done.

There are three clipping diodes in an SD-1, so how is it possible to add a fourth? Adding another diode in series or parallel to D4, 5 or 6 won't accomplish
what is described in the quoted post above. It will still be asymmetrical clipping.

11Gauge?

Actually, if you add another silicon diode in series with D4, it will be symmetrical. The trick is getting two diodes in a spot designed for one.

...Not a big deal really. You solder the two series units together before bending them into a triangle shape, and inserting the entire unit into D4's slot. Pedal builders do it all the time with stuff in series, or when you have an odd resistor, and have to build it out of two standard value ones.

AAMOF, this "series shoehorning" technique is necessary for modding an SD-1 into a ZenDrive:

D4: 2N7000 mosfet and BAT41 in series
D5: 2N7000 mosfet and BAT41 in series
D6: BAT41

Alternatively, you can put just the mosfet in D5, and two BAT41's in series in D6.

The possibilities are only limited by your imagination. Run 3 in series in D4 (build a rectangle) and 2 in series in either D5 or D6, and you have the diode array of an Xotic RC booster.

...Or you could build a daughterboard from perfboard or similar, and arrange a monster diode array. Try duplicating the Crowther Prunes and Custard clipping diode setup, just to say that you did it!

Happy diode chaining!

BTW - 3 silicon diodes in series yields a threshold of ~1.8V, which is almost the same as most common LED's. Xotic could have saved themselves a bit of trouble by going this route. But in all fairness, the RC and AC use the exact same pcb, and the RC requires the 3 diode setup that the SD-1 uses. So Xotic would be jumpering the RC relegated boards all to heck...

Yousa gonna hafta pardun my eegnorunce hear -

But if D4 and 6 are clipping one have of the signal (waveform\sinewave, whatever) and D5 is clipping the other half, then how does putting two diodes in series in D4 change that? Wouldn't an additional independent diode working in tandem with D5 be needed for symmetrical clipping?

I'm confused...

D4 is clipping one half by itself.

D5 and D6 are in series and are clipping the other half, at double the threshold.

So leave D5 and D6 stock, and add another diode in series with the singular D4, and the clipping becomes symmetrical. Two one way and now two the other way.

Maybe it might work better to think of the pair in D4's place as D4a and D4b. Think of those as two cars in the northbound lane, and the D5/D6 pair as two cars in the southbound...

Probably clear as mud, eh? Do you have a schematic? If not, here's one.

Wull...

There's something I'm not communicating and\or understanding. My limited knowledge of the subject at hand is surely coming into play here. BUT!

Why is it that "seperate" diodes (i.e. each having their own location on a PCB)
sounds different than stacking diodes in series? I know when I've done this it creates a thicker distortion, but this doesn't seem to sound the same as what happens when I remove or replace a diode in a given circuit (in this case, an SD-1.)

Again, I'm sure my ignorance explains much.

Wull...

There's something I'm not communicating and\or understanding. My limited knowledge of the subject at hand is surely coming into play here. BUT!

Why is it that "seperate" diodes (i.e. each having their own location on a PCB)
sounds different than stacking diodes in series? I know when I've done this it creates a thicker distortion, but this doesn't seem to sound the same as what happens when I remove or replace a diode in a given circuit (in this case, an SD-1.)

Again, I'm sure my ignorance explains much.

By stacking, do you mean "piggybacking" to an existing diode? If so, they would be in parallel - quite different!

I think you might be getting thrown by how the 3 diodes are oriented on the circuitboard. It can be confusing, since all 3 point the same way on the board (no way to distinguish their arrangement without tracing the circuitboard or analyzing the schematic.

It might be simpler if you "revert" back to a stock TS symmetrical setup. All that this involves is replacing either D5 or D6 with a piece of wire. You now have two diodes in parallel - stock TS clipping.

...So, building upon that, D5 and D6 in a stock SD-1 are in series. D4 is by itself, clipping in the other direction, in parallel with D5/D6.

It may also be helpful to think of D5/D6 as a single diode as configured in a stock SD-1.

I'm guessing that you may also be confused about the difference between diodes in series or parallel.

...Diodes in series are chained together "end to end." Just like two batteries in a flashlight. And just like that flashlight, you get a multiplied effect. In the case of the flashlight, a pair of 1.5V batteries gives you 3V total. In the case of your clipping diodes, a pair of diodes that conduct at .6V now conduct at 1.2V, as if it were a single diode. The higher this number, the larger the threshold - it takes a much bigger signal to get clipped.

...Diodes in parallel run "side by side," "stacked," "piggybacked," or any other nomenclature that you prefer to use. In parallel, diodes must have their polarities going in different directions (in most instances), or you will only clip one half of the signal. Once you have the first pair in parallel, you can add others (in PARALLEL), but your threshold will not be increased. There's little IMO if any benefits to running additional diodes in parallel with an existing pair. So you can forget about this situation, just for clarity.

IT ALL COMES DOWN TO THE THRESHOLD (for the most part) with clipping diodes - nice and simple! Different single diodes give you different fixed thresholds, depending on the voltage that they conduct at. You combine them in series to get bigger fixed thresholds - they act like a SINGLE diode in series.

Are we getting any closer? Did you look at the schematic? If not, look at it now, and note in the schematic (not on the circuitboard!) how D4 is oriented, compared to D5/D6. Review the above small novel, and it should make sense.

Ooops, I should be careful about the words I use. No, by stacking, I just meant diodes in series. End to end, not side by side, which would be parallel.

I've looked at the schematic (many times, I have a hard copy printed out for when I'm tweaking the pedals I have already) and that's not really where I'm getting hung up. I think the problem really stems from my limited knowledge, coupled with a lack of appropriate terminology to describe what I'm thinking.

so would there be any difference between an SD-1 designed to have a fourth diode for asymmetric clipping, and putting two together in D4 in series?

so would there be any difference between an SD-1 designed to have a fourth diode for asymmetric clipping, and putting two together in D4 in series?

If you're adding another diode in series with D4, the clipping will not be asymmetrical, because you have the series pair of D5/D6 running in the other direction. Once again, it might help to think of D5/D6 as one diode, and D4a/D4b as one diode.

Stock SD-1 diode arrangement (asymmetrical):

<-----D4-------
--D5-->--D6-->

SD-1 converted to TS (stock) symmetrical:

<-------D4---------
--D5-->--jumper--

SD-1 converted to 4 diodes, symmetrical:

<--D4a--<D4b--
--D5-->---D6-->

I meant symmetrical. I'm just mildly retarded, that's all. I had to go back to the first few posts to get it straight, but I'm back on target. (I think...)

So what's the difference (tonally) between symmetrical TS style, and adding a fourth diode?

Never mind that last one. I answered my own question by actually trying it.