ODR-1 "anti-parallel" diodes

[jessenator]

https://www.nordland-electronics.de/en/blog/odr-1.html

So I was reading up about the development of the ODR-1 and in my quest to actually know what it is I'm actually doing when I'm lost in Eagle layouts I thought I'd ask a bit more of what's going on here, and if it's worth tinkering.

Firstly, I'm guessing that the two pairs of diodes here should be paired appropriately—I've read various takes on the whole pairing process, but I'm more interested in whether or not they should, all four of them, have the same FV to be suitably "anti-parallel", yeah?


And again, my swiss-cheese knowledge painfully manifested here, would changing these diode pairs affect the cleanliness of the pedal's character? I'm assuming the 1N914 was chosen for its properties specifically, but then again we (collectively) have beaten the dead horse that offends so many in other circuits' discussions, so...

I may just socket them anyways, but has anyone tried different types and have one they'd recommend... or configurations even. Something like an anti-parallel, anti-symmetrical monstrosity?

[mauman]

It might be useful to see how the circuit designer Kai Tachibana approached this.  In his original ODR-1, all 4 diodes are the same type (4148 silicon) with the same forward voltage drop (around 0.6V).  In his updated Norland ORD-C, four equivalent silicon diodes are used, but with an "overdrive de-compress" pot that can fade in two LEDs in series with the two feedback diodes.  This allows the feedback loop Vf to vary from 0.6 (no LED) to around 2.6 or so (full LED), depending on the LED color.  The clip-to-ground Vf remains at 0.6V.

Matching the two diodes in the feedback loop will give you symmetrical clipping (same amount of reduction on positive and negative waveforms.)  Mismatching them will give you asymmetrical clipping, which some people like.  Same for the two clip-to-ground diodes, matching those = symmetric positive and negative clipping, mismatching = asymmetric.  So it depends on what you're after!  Socketing and experimenting is useful.

[jessenator]

Thanks for the detailed reply, mauman!

I'll definitely socket them then. That odr-c sounds fascinating with that variable in the LEDs. This particular specimen is going to be a gift to a friend, and it'll be fun to tailor it just for them.

[gordo]

Hmmm, I may just have to open up the Laureate and check this out.

[mauman]

The ODR-1 (with added bass control) is one of my two all-time favorite OD, the other being the MT-10 that Brian just added.  I haven't build an ODR-C yet but it's on the list.