Fun fact- both of these pedals have OD in their names.
The OD808 was my first overdrive pedal. Of my many TS builds, on one (a Son of Screamer) ever got 100% there. Others were close, but the OD808 just had a little bit more creaminess to it. Having read all sorts of BS on the interwebs about TS versions, I triehd to trace it a few years ago, copying the PCB, and cloning it part for part. I never got around to figuring out what parts on the main PCB connected to the daughter board, and it’s sat on my shelf ever since. I just dug it out, and this is what I found:
– Clipping diodes are orange with a white stripe marking the cathode. Maxon’s marketing claims they’re Panasonic MA150s, which I’ve never seen for sale anywhere.
– Opamp is a JRC4558D. As expected.
– The input cap (C1) is 20nF. Not 22nF. True to the original TS808. In fact, all the component values are true to RG Keen’s schematic in his Technology of the Tube Screamer article. 51pf, not 47pf. 51k, not 47k. The two .22uF caps are tantalum.
– Analogman’s article is incorrect, kind of. The OD808 is not a TS10 circuit (at least the part that matters). It’s a TS9 circuit. There is no Ra (220R in series with opamp). It DOES, however, have the extra emitter follow in the input buffer. Not sure how much that matters since it’s for the bypass. The input buffer transistor is connected to 9v, not some bias voltage as RG’s article says the TS10’s is. The shunt resistor in the output buffer is 100k and the series resistor is 470R, same as the TS9.
– TR1-4 are C1815s. Q1-2 are K246.
– “It should be noted that the Reissue Series OD808 uses different output resistors than the original version. Vintage TS808’s are susceptible to microphonic noise due to static electricity buildup on the chassis. To improve performance, the positions of the output resistors on the reissue OD808 were reversed and their values increased in order to reduce noise levels. This circuit change has no audible affect on the sound of the unit, save for reducing the noise levels.”
That’s a lot of words for trying to explain that it has the TS9 output resistors. But this is the one area where the positions of the components differ from RG’s schematic. RG has RB -> 10uF -> Rc-to-ground/Output. The OD808 has 10uF->Rc-to-ground/Rb->Output. Is this what Maxon meant by reversing the positions of the resistors? They put the series resistors after the output cap and shunt resistor instead of in front of them. I don’t think this should matter electronically, but what do I know?
This is the coolest disappointment ever.
The Pearl Over Drive (the space is part of it’s name), is such a great idea. It’s a TS style overdrive, with clipping diodes in the neg feedback look. It’s one of the smoother sounding overdrives I’ve heard, probably due to the 1k resistors in series with the clippers. With the EQ Gain at noon, it sounds pretty transparent. No crazy mid hump. But the parametric EQ lets you give it any hump or scoop you want.
The disappointment: It can’t get clean. Even with the Over Drive knob turned all the way down, it’s still dirty. And doesn’t’ boost very much at all. For whatever reason, there’s a 10k resistor in series with the pot. That’s too much. Swapping it for 1k per BYOC and Aion’s suggestions allows it to get clean. And that doesn’t seem to reduce your max gain. The range of drive kind of sucks. It’s goes from a little dirty to entirely saturated pretty early on the knob’s rotation. Reducing that 10k is a must.
The cool: The parametric EQ is friggin’ sweet. Boosting 600hz makes it a great boost for my Dual Rec. Really, whatever frequency you’re lacking or have too much of, you can deal with. It’s incredibly versatile in that regard. And dealing with that 10k resistor makes it even more versatile. Set clean, it can be a treble boost, or whatever kind of boost you want. The enclosure is pretty cool too.
Every schematic for this thing has issues. After discussing it with BYOC, Aion, building two of them, and then getting my own unit, I can safely say that I know where to run the wires. They don’t necessarily go where the schematic says they do. That doesn’t mean it won’t work the same way, just that what’s on paper isn’t how it was assembled. Aion’s Fractal project is the only place to get a PCB that I know of, and BYOC’s Parametric Overdrive is a great kit for those who don’t want to source their own parts. Their PCB should be good, but don’t trust the BYOC schematic. It’s wrong.
For what it’s worth, my cheapo China-sourced 1S1558s that are probably not really 1S1588s seem to sound about the same as the real things in the OD-05. I need to turn this circuit into a lab unit and figure out what mods make it all the cooler.
Here’s the schematic that shows exactly what’s in my unit: