Boss OD-1 Improved Schematic

[phillip]

After a few requests, here's a schematic of the single IC Boss OD-1, with improved parts values for more output, more input impedance, lower noise, and more overdrive range.  Part values highlighted in red are the parts that were modified.

The parts numbers on this schematic do not match the part numbers on the original Boss OD-1 schematic (or circuit board, if it's numbered).  These numbers are there for reference only.

I would recommend the AVX Boxed metal film capacitors from Mouser for this circuit, especially for the two 1uF capacitors.  

http://axiseffects.home.att.net/misc/OD1_improved.gif

Enjoy!
Phillip

[cd]

Which is supposed to be the lower noise mod?  The IC swap?  'Cause the higher input impedance has the potential for more noise.  The transistors are emitter follower buffers (no gain) so their noise potential is minimal as well.

If you're going to go to the trouble of changing the OD range, I would also change C4 to .047u like it is on the quad opamp OD-1.  It will add a lot more low end response and make the OD range change even more apparent, unless you like the thin stock sound, of course.  Or you could leave C4 stock and change C5 to something huge like 10u which would some similar but slightly different.

[phillip]

The MPSA18 transistors and the 2134PA will go a long ways towards lower noise, along with metal film resistors and other good stuff like that.  At any rate, using low noise transistors like the MPSA18 or 2N5089 on the input and output buffers are quite an improvement over the originals.  

I've replaced the original input and output buffer transistors in my SD-1 with the MPSA18 and quite a bit of the hiss went away with them.  The MPSA18 isn't a direct drop-in replacement for the originals, which I beleive had the B-C-E pinout...while the A18 has C-B-E.  I had to twist the collector and base leads around to get them to fit.

Phillip