Boss SD-1 to OD-1 Conversion

[soupbone]

Having a little problem trying to figure out this mod.I'm doing the Boss SD-1 to OD-1 conversion from this page;http://www.erikhansen.net/p/pedal-mods_23.html You'll see Boss Pedal Mods.When you click on the link,it will be a pdf file.I wanted to do the mods,but keep the tone knob.You have to change the inverting input (pin 2) to the non-inverting input (pin 3).I wanted to keep the tone knob,so i'm not sure which pad's on the pcb should be desoldered,or left alone.Here's also the schematics for both pedals; http://www.hobby-hour.com/electronics/s/od1-overdrive.php http://www.hobby-hour.com/electro.../s/sd1-super-overdrive.php Any help would be greatly appreciated!

[slacker]

If you want to keep the tone knob you have to leave the second opamp stage how it is in the SD-1, it's part of the tone control, just do the R1 and C2 changes, leave everything else how it is. Set the tone control to 12 o'clock and it will sound the same as the OD-1.

[Mark Hammer]

I made myself an old-school OD-1, using a 3403 quad op-amp (first issue version of the pedal), and quite like it.  However, like most TS derivatives, it often needs more bass than it comes with.  Since the stock SD-1 Tone pot is a suitable value, I would suggest borrowing a trick from the Rat and numerous other TS-inspired pedals.  Reconfigure that now-spare pot so that it becomes a secondary parallel path to the R6/C3 path. 

R6/C3 sets both the gain and the low-end rolloff.  Often, when people mod their TS/SD for more bass, they raise the value of C3, making it 100nf or even 470nf, so that the bass is not rolled off until way down low.  However, if one uses a pot and selected cap value, you can make that bass retention variable.

Let's stick that spare pot in series with a 3k9 resistor and a 330nf cap.  With the tone pot set for max resistance (20k), we now have 23k9 and 330nf as a parallel path to ground.  Since the 4k7 path is so much lower, the added pot/resistor/cap path will have no audible impact.  As the pot resistance is decreased, a little more gain in the bass range is applied, but the stuff above 720hz is still clearly getting the benefit.  As the pot value approaches around 4k, you start to hang onto more of the bass in an audible way.  When the pot hits 0 ohms, and you just have the 3k9 and 330nf, that becomes the sort of "preferred" path, and you increase the overall max gain beyond what a stock SD-1 or OD-1 provides, and extend the bandwidth down to 123hz, which provides even more clipping in the lower registers.  If yo want the bass, but not the super-saturated sound, just turn the gain down.

[soupbone]

If you want to keep the tone knob you have to leave the second opamp stage how it is in the SD-1, it's part of the tone control, just do the R1 and C2 changes, leave everything else how it is. Set the tone control to 12 o'clock and it will sound the same as the OD-1.

Thanks!

[soupbone]

I made myself an old-school OD-1, using a 3403 quad op-amp (first issue version of the pedal), and quite like it.  However, like most TS derivatives, it often needs more bass than it comes with.  Since the stock SD-1 Tone pot is a suitable value, I would suggest borrowing a trick from the Rat and numerous other TS-inspired pedals.  Reconfigure that now-spare pot so that it becomes a secondary parallel path to the R6/C3 path. 

R6/C3 sets both the gain and the low-end rolloff.  Often, when people mod their TS/SD for more bass, they raise the value of C3, making it 100nf or even 470nf, so that the bass is not rolled off until way down low.  However, if one uses a pot and selected cap value, you can make that bass retention variable.

Let's stick that spare pot in series with a 3k9 resistor and a 330nf cap.  With the tone pot set for max resistance (20k), we now have 23k9 and 330nf as a parallel path to ground.  Since the 4k7 path is so much lower, the added pot/resistor/cap path will have no audible impact.  As the pot resistance is decreased, a little more gain in the bass range is applied, but the stuff above 720hz is still clearly getting the benefit.  As the pot value approaches around 4k, you start to hang onto more of the bass in an audible way.  When the pot hits 0 ohms, and you just have the 3k9 and 330nf, that becomes the sort of "preferred" path, and you increase the overall max gain beyond what a stock SD-1 or OD-1 provides, and extend the bandwidth down to 123hz, which provides even more clipping in the lower registers.  If yo want the bass, but not the super-saturated sound, just turn the gain down.

Good stuff Mark!