According to the schematics I have, OD2 doesn't contain any opamp-based ICs. It is based on discrete opamps implemented using discrete transistors (2 JFETs + one pnp BJT).
I've noticed that the SD1 and SD2 sound VERY similar, but the SD1 has that slight tubescreamer-esque "mid hump" whereas the SD2 doesn't. Is that mostly a function of the JRC4558 vs 2M5218AL chip?
I guess with tubescreamer-esque you are referring to the crunch channel of the SD2. The overdrive section is based on the same principle as the SD-1 but using different component values. For instance, SD2 used 2 LEDs and a Si diode for clipping and the frequency cut off is ~50Hz. The SD1 uses 3 Si diodes and a frequency cut off of 720 Hz. Since SD2 covers a wider frequency range the "mid hump" is masked.
I don't think the opamp chip on its own can produce the "mid hump". The difference in sound due to different opamps is a rather a subtle one.
The lead channel is much more complicated and uses also LEDs as clippers.
Are OD2 & SD2 JRC4558 based?
Posted - 03/24/2009 : 03:51:42
