Aquaticwombat
Member
Has anyone looked inside on this to see the differences with the original? It says it has a pair of germanium diodes. Is there an easy way to use the standard ADHD board to do the same thing?
Germanium OCD
- Thread starter Aquaticwombat
- Start date
The ad copy from here - https://www.fulltone.com/products/custom-shop-ocd-germanium - says:
"The earliest OCDs used 2 x Mosfets plus 1 x Germanium diode, but very quickly these diodes became harder and harder to find, and they became expensive.
Recently I stumbled across a reasonably large stash of the right kind of Germanium diodes so I ponied-up and bought all of them. So I decided to do a run of the ultimate OCD: a Custom Shop offering with a few circuit tweaks using 2 x Mosfets plus 2 x Germanium diodes"
If this schematic is to be believed
Then the "earliest OCDs" had the one germanium diode in series with one of the 2n7000s, so it's probably safe to assume the Germanium OCD did this twice.
You could do this with an ADHD board, solder a germanium diode to the two tied-together legs of the 2n7000 and put that into the right pads of Q2 and Q3.
"The earliest OCDs used 2 x Mosfets plus 1 x Germanium diode, but very quickly these diodes became harder and harder to find, and they became expensive.
Recently I stumbled across a reasonably large stash of the right kind of Germanium diodes so I ponied-up and bought all of them. So I decided to do a run of the ultimate OCD: a Custom Shop offering with a few circuit tweaks using 2 x Mosfets plus 2 x Germanium diodes"
If this schematic is to be believed
Then the "earliest OCDs" had the one germanium diode in series with one of the 2n7000s, so it's probably safe to assume the Germanium OCD did this twice.
You could do this with an ADHD board, solder a germanium diode to the two tied-together legs of the 2n7000 and put that into the right pads of Q2 and Q3.
I'm sorry if I sound harsh but this sounds like bollocks to me! I suspect that some manufacturers do this because most players won't know the difference between a transistor and a diode and if you can say your pedal has germanium in it then it has some magical element of mojo in it.
But then I guess Mike Fuller is known for being honest and understanding and to never use hyperbole in his product descriptions so I guess an OCD with Ge diodes must be amazing.
But then I guess Mike Fuller is known for being honest and understanding and to never use hyperbole in his product descriptions so I guess an OCD with Ge diodes must be amazing.
benny_profane
Well-known member
I would imagine that it’s using the Ge diode to block the body diode of the clipping MOSFET. Some iterations of the OCD don’t include a blocking diode and have the clipping arranged such that the body diode conducts before the gate junction of the MOSFET.
jimilee
Well-known member
This ^^^
Aquaticwombat
Member
Can someone give me a visual of how to do this. My brain is apparently too clogged with soldering fumes. The dirtiest MS Paint sketch would be more than sufficient.
benny_profane
Well-known member
Reference this write-up by Jack Orman and also take a look at the Zendrive clipping arrangement to see how to use the series diode properly. Even though that's soft clipping, you can see the general principle.
giovanni
Well-known member
A hint of sarcasm there?
jeffwhitfield
Well-known member
Ok, I'm not an expert so I'm just guessing. Based on the schematic of the Infatuated Overdrive, it appears that the Ge diode is simply being used to mimick a typical asymmetrical configuration. In this case though they're using two transistors with the Ge acting as the third. Seems to me this is an easier way to create asymmetrical clipping without the use of three transistors. However, like Fulltone seems to say in the description of their OCD Ge pedal, the right diode is required. I would guess that you would need a Ge diode with a reverse voltage that matches closely with transistor. So...it's not bullshit really...well...sort of. It's not true Ge clipping. One Ge diode does not a Ge pedal make. More of a hybrid really.
jeffwhitfield
Well-known member
Yup. It's the kind of shit we see all the time, right? Throwing any Germanium component in a pedal automatically makes it a Germanium pedal, right? You can market that....and people will buy it and not know they're getting ripped off.A hint of sarcasm there?
benny_profane
Well-known member
One MOSFET device (drain to gate, series with source) itself provides asymmetrical clipping due to the body, or substrate, diode (i.e., from source to drain) and the gate junction.
The Ge diode is used to block the body diode of the MOSFET from conducting when the gate junction isn't forward biased. 'Reverse voltage' has nothing to do with it. Since it's arranged in series with the MOSFET (D-G->S), it's used to block the S-D body diode from conducting. If you arrange two MOSFETs as D-G->S + S->G-D, you get the gate junction MOSFET clipping, block the body diode from conducting, and you don't waste a Ge diode.
DAJE
Well-known member
If you took all the hyperbole out of pedal marketing, then all theYup. It's the kind of shit we see all the time, right? Throwing any Germanium component in a pedal automatically makes it a Germanium pedal, right? You can market that....and people will buy it and not know they're getting ripped off.
jeffwhitfield
Well-known member
Thanks for the explanation. So it would seem that the Ge diode thing isn't really required if the circuit was updated to the config that you outlined, right? If that's the case then, yeah, I suppose the Ge diode thing is bullshit.
jeffwhitfield
Well-known member
"But...it's $5000. It's like buying a Lambourghini or Ferrari, right? It'll sound better than anything!"
Umm...no, chief...it's not like buying an expensive sports car because, unlike a sports car, we can build a carbon copy of that $5000 pedal any day of the week. Nothing in there that can't be done by a Joe pedal builder. That's what many of these folks don't get.
benny_profane
Well-known member
It all depends on what you're trying to accomplish with the clipping. E.g., the Zendrive uses a Ge diode in addition to the MOSFET clipping and Schottky blocking diodes. Keep in mind that the Gate junction Vf is pretty high with a very soft knee. In some cases, you'll get to op-amp saturation before the MOSFET clipping even conducts. Try out some variants on the breadboard (use the AMZ link above for more ideas) and see what works for you. As implemented in the OCD, I believe making 'germanium' the defining feature of the pedal is rather disingenuous, yes.Thanks for the explanation. So it would seem that the Ge diode thing isn't really required if the circuit was updated to the config that you outlined, right? If that's the case then, yeah, I suppose the Ge diode thing is bullshit.
After much confusion and reading about this in the past, it very much seems that the ZenDrive Schottky diode (and Ge on one side) are NOT acting as a blocking diode. It’s backwards for that use. So what you have is the regular body diode in series with the schottky.
Look up mosfet body diode and look at the zendrive schem. The bat41s are in the same direction as the body diode. (If anyone can contradict this I’d be curious to hear). For what it’s worth, the Jack Orman article does say that the body diode clips softer than a regular si.
If it were me adding Ge to the OCD, I’d put them in series with the body diode (not blocking). But idk what it actually is.
Look up mosfet body diode and look at the zendrive schem. The bat41s are in the same direction as the body diode. (If anyone can contradict this I’d be curious to hear). For what it’s worth, the Jack Orman article does say that the body diode clips softer than a regular si.
If it were me adding Ge to the OCD, I’d put them in series with the body diode (not blocking). But idk what it actually is.
benny_profane
Well-known member
You are right—that my mistake above. The Schottky should be indeed reversed. However, in the soft clipping arrangement, I'm not convinced that the MOSFET gate junction will conduct due to the soft knee and the high Vf. If the Zendrive were indeed setup in that way, I'd be interested to see if the scope showed much of a difference between the MOSFET arrangement and op-amp clipping.
Big Monk
Well-known member
The only caveat here would be this: Many of us don’t compare them to the originals.
It’s fine to say your Klone blows away a real Klon if you have AB’d them. Hell, it’s fine to say you THINK your Klone blows away a real Klon even if you haven’t. As long as we are all on the same page about the subjective nature of tone, we can say whatever we want about DIY vs. the real thing.
Now, I’m not a mojo guy so I wouldn’t want to be misconstrued as being such, but there have been times when I’ve kept the commercial version of a pedal because, try as I may, that cheaper version I built didn’t sound the same.
You are right in the theoretical sense though: There’s nothing magical about circuit building and oftentimes there is only a thin layer of bullshit between that $200 pedal and the one you make in your basement for $40.
