Author Topic: EgoDriver/Fulltone OCD architecture  (Read 835 times)


  • Diode Destroyer
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EgoDriver/Fulltone OCD architecture
« on: September 06, 2019, 02:02:27 AM »
Greetings everyone,

I was wandering if someone can help me with understanding a schematic.
Can't understand if EgoDriver is an overdrive or a distortion box.
EgoDriver's clipping stage does not look like either to me - it's not going directly to the ground, and does not seem to go into opamp's feedback, but I may be wrong.

Thanks in advance!


  • Solder Ninja
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  • TJ
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Re: EgoDriver/Fulltone OCD architecture
« Reply #1 on: September 06, 2019, 05:19:57 AM »
Not sure if there is such a strict distinction between overdrive and distortion. The egodriver applies hard clipping with the diode/mosfets (and it is wired to use the body diode of the mosfet). The clippers do not go to ground but to the reference voltage VB, which is appropriate as the signal that needs to be clipped sits around that voltage. If the clippers would go to ground, in this schematic, only one half of the waveform would be clipped. So in circuits with hard clipping to ground you will see a coupling cap after the opamp and before the clipping section to block the DC bias.

Now, in practice, since there are no diodes in the feedback loop, the opamp may start to clip as well at higher settings of the gain pot. So the opamp may also be part of the story.

I think my analysis is more or less correct, but otherwise Iím sure somebody will correct me  ::)


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Re: EgoDriver/Fulltone OCD architecture
« Reply #2 on: September 06, 2019, 05:39:52 AM »
In general, the distinctions between overdrive and distortion tend to fall into these criteria (IMO):
1- Overdrive is meant to compliment and enhance a tone that is already in or near breakup.
2 - Overdrive retains some element of clean signal layered into the clipped waveform.
3 - Distortion doesn't require 1 or 2.

The OCD is an overdrive by that definition. However, I would consider a Rat more of a distortion even though it has some elements of 1 and 2 and is pretty similar to an OCD. Both have non-inverted gain stages which means some clean is layered in the result. But, they sound radically different.

The biggest difference (again, IMO) between soft and hard clipping is that hard clipping can be more responsive to picking dynamics. For example, in the OCD you can actually get a fairly clean sounding signal if you pick very lightly. As you increase the picking dynamic the output clips proportionately and the overall perceived compression increases. This can also be true for overdrives, but sometimes to a lesser extent.

Then again, I don't think these are very important or needed distinctions.
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