# Germanium OCD



## Aquaticwombat (May 19, 2022)

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?


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## manfesto (May 19, 2022)

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









						Infatuated Overdrive PCB - delyk PCBs
					

Layout designed by delyk PCBs




					www.delykpcb.com
				




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.


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## HamishR (May 22, 2022)

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.


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## benny_profane (May 22, 2022)

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.


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## jimilee (May 22, 2022)

benny_profane said:


> 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.


This ^^^


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## Aquaticwombat (May 22, 2022)

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.


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## benny_profane (May 22, 2022)

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.


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## giovanni (May 22, 2022)

HamishR said:


> 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.


A hint of sarcasm there?


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## jeffwhitfield (May 22, 2022)

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.


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## jeffwhitfield (May 22, 2022)

giovanni said:


> A hint of sarcasm there?


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.


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## HamishR (May 22, 2022)

And how much does a Ge diode cost? So they're getting more expensive. It's not like we're talking $50 per diode.


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## benny_profane (May 22, 2022)

jeffwhitfield said:


> Seems to me this is an easier way to create asymmetrical clipping without the use of three transistors.


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.


jeffwhitfield said:


> I would guess that you would need a Ge diode with a reverse voltage that matches closely with transistor.


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.


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## DAJE (May 22, 2022)

jeffwhitfield said:


> 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.


If you took all the hyperbole out of pedal marketing, then all the suckers golden eared tone fiends would have to find something else to waste invest their money on. No more $5000 Centaurs if everyone understood that you and I can make the exact same thing for $50.


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## jeffwhitfield (May 23, 2022)

benny_profane said:


> 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.


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.


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## jeffwhitfield (May 23, 2022)

DAJE said:


> If you took all the hyperbole out of pedal marketing, then all the suckers golden eared tone fiends would have to find something else to waste invest their money on. No more $5000 Centaurs if everyone understood that you and I can make the exact same thing for $50.


"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.


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## benny_profane (May 23, 2022)

jeffwhitfield said:


> 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.


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.


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## HamishR (May 27, 2022)

A friend of mine just sold his Klon that he'd bought years ago for not so much $$. Now he's looking for guitars to buy!


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## phi1 (May 27, 2022)

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.


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## benny_profane (May 27, 2022)

phi1 said:


> The bat41s are in the same direction as the body diode. (If anyone can contradict this I’d be curious to hear).


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.


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## Big Monk (May 27, 2022)

jeffwhitfield said:


> "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.



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.


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## jeffwhitfield (May 27, 2022)

Big Monk said:


> 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.
> 
> ...


True, true. I think the only way to really know how one DIY pedal stacks up against an original is to use a spectrometer and measure the frequency response and such. Even then, there are elements that can't really be measured.

And you're right about the "thin layer of bullshit". That's definitely the case with lower priced pedals. But with something like a Klon or a KoT, that thin layer quickly turns into a thicker one in no time flat. The thing I argue is that with most guitar sounds you don't necessarily hear them much by themselves. They're usually mixed in with other things. At that point, can you really discern a real Klon from a well designed Klone? Or a real KoT from a good copy? I tend to think not. 

The differences are largely subjective. I think we tend to hear things that aren't really there. Or, at the very least, get peace of mind knowing that we have an original as opposed to a copy...which in our mind is somehow inferior to the original. One is not really better than the other. It's all in the (err) "ear of the beholder".


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## Lewage (Sep 9, 2022)

manfesto said:


> 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 am building 2 of these and figure its worth messing around with tho see if it really makes a difference. Are you saying that connecting the ge diode from leg 1 to 3 of the 2n7000 will accomplish this?


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## SillyOctpuss (Sep 9, 2022)

There's a thread and some schematics on the germanium OCD at freestompboxes.  I'm out at the minute but will have a look for the thread when I get home later


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## Chuck D. Bones (Sep 10, 2022)

benny_profane said:


> 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.


Some of the OCD schematics I've seen have a Ge diode in series with one of the MOSFETs, other schematics have no series diode.  When there is a series diode, it's pointing the same direction as the body diode, therefore it's not blocking anything.  I posted some MOSFET diode curves here.


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## Barry (Sep 10, 2022)

I think I have one of these laying around, I'll open it up and snap a photo if anyone is interested


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## Robert (Sep 10, 2022)

Definitely would be interested.


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## Barry (Sep 10, 2022)

Robert said:


> Definitely would be interested.


Ok, I'll dig it out


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## Feral Feline (Sep 10, 2022)

Lewage said:


> I am building 2 of these and figure its worth messing around with tho see if it really makes a difference. Are you saying that connecting the ge diode from leg 1 to 3 of the 2n7000 will accomplish this?



You may be already aware of the following, but for the aid of those unfamiliar...

Some background info:








						Mosfet Body Diodes - AMZ-FX Guitar Effects Blog
					

Mosfets are 4-terminal devices with a gate that controls the conduction of the drain to source channel. The body (or substrate) of the typical n-channel enhancement mosfet is a P-type material with the drain and source formed from N-type materials. The oxide layer insulates the metal gate...




					www.muzique.com
				




Applying the knowledge:




__





						AMZ - Guitar Effects & diode clipping
					

How to use mosfet transistors and zener diodes for clipping in guitar fx pedals.




					www.muzique.com
				








 Diagram from the latter AMZ site above.


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## Barry (Sep 10, 2022)

OCD GE


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## Barry (Sep 10, 2022)




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## Barry (Sep 10, 2022)

Robert, I can send it down if you want


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## Chuck D. Bones (Sep 10, 2022)

Those Ge diodes have a single green band, yes?  That would make them Д9Ж (D9J).  They're hard-wired to the MOSFETs (Q2 & Q3).  The diodes, MOSFETs and wires are glued down as a strain relief.  'Cuz clear goop would just be silly.

Sure are a lotta extra parts on that board compared to an OCD or Alpha Drive.


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## Robert (Sep 10, 2022)

Chuck D. Bones said:


> Sure are a lotta extra parts on that board compared to an OCD or Alpha Drive.



That's the newest version of the OCD with "Enhanced Bypass". 



			https://docs.pedalpcb.com/project/ADHD.pdf


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## Robert (Sep 10, 2022)

Barry said:


> Robert, I can send it down if you want



Do you see a cut trace anywhere around where those germanium diodes connect to the SMD transistors?

EDIT: Nevermind, I think I see it in your second pic,  right above C4.

Looks like he just added a germanium diode in series with each MOSFET clipper.



manfesto said:


> 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.



I believe you are correct.   Although I didn't realize this was built on the V2, I thought the Ge version was older than that.


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## Chuck D. Bones (Sep 10, 2022)

I wonder if there is a market for carbon comp resistors in SMD packages?


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## benny_profane (Sep 10, 2022)

This board looks so hacky.


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## Robert (Sep 10, 2022)

benny_profane said:


> This board looks so hacky.



They haven't always been so bad...

Oh wait... yes, yes they have.    But to be fair.... this one doesn't oscillate.


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## K Pedals (Sep 11, 2022)

Chuck D. Bones said:


> Those Ge diodes have a single green band, yes?  That would make them Д9Ж (D9J).  They're hard-wired to the MOSFETs (Q2 & Q3).  The diodes, MOSFETs and wires are glued down as a strain relief.  'Cuz clear goop would just be silly.
> 
> Sure are a lotta extra parts on that board compared to an OCD or Alpha Drive.


There are some German and Japanese 1N314’s that have a sing green band as well… these look more like one of those to me.?.?


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## SillyOctpuss (Sep 11, 2022)

They look a lot like the green band unizen 1n34a.  I have some I can take a picture of later if it would help? 

@Barry is this the limited edition candy Red germanium OCD from around 2 or 3 years ago? 

I thought the germanium ocds only used one germanium diode with one of the mosfets but your pedal has one for each.  Maybe that's the difference between the customer shop red one and the older units?  The newer one is a V2 with a germanium diode on each mosfet


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## Barry (Sep 11, 2022)

SillyOctpuss said:


> They look a lot like the green band unizen 1n34a.  I have some I can take a picture of later if it would help?
> 
> @Barry is this the limited edition candy Red germanium OCD from around 2 or 3 years ago?
> 
> I thought the germanium ocds only used one germanium diode with one of the mosfets but your pedal has one for each.  Maybe that's the difference between the customer shop red one and the older units?  The newer one is a V2 with a germanium diode on each mosfet


Mine is green


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## fig (Sep 11, 2022)

Robert said:


> They haven't always been so bad...
> 
> Oh wait... yes, yes they have.    But to be fair.... this one doesn't oscillate.
> 
> View attachment 32084


Do you have a DMM and / or audio probe ? Try soaking it in Palmolive.


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## Robert (Sep 11, 2022)

fig said:


> Do you have a DMM and / or audio probe ? Try soaking it in Palmolive.




Will this work?   Palmolive?  I can see where that might help with the friction.


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## fig (Sep 11, 2022)

Ribbed...groovy!


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## ClassicFuzz (Sep 11, 2022)

A very helpful thread. Thanks for all your input. I think I might give this a go with a V2 layout. How could one implement a switch to switch between V2 and Custom GE?


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## Robert (Sep 11, 2022)

Assuming I am correct about the connection of the diodes, you would just wire up a DPDT switch to jump across both diodes.


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## ClassicFuzz (Sep 11, 2022)

Robert said:


> Assuming I am correct about the connection of the diodes, you would just wire up a DPDT switch to jump across both diodes.


so basically drill them together asymmetrically and connect them to lug 1 & 4 of the switch and then one wire between lug 2 and source (transistor 1) and between lug 5 and drain (trainstor 2), right?


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## ClassicFuzz (Sep 11, 2022)

Chuck D. Bones said:


> Those Ge diodes have a single green band, yes?  That would make them Д9Ж (D9J).  They're hard-wired to the MOSFETs (Q2 & Q3).  The diodes, MOSFETs and wires are glued down as a strain relief.  'Cuz clear goop would just be silly.
> 
> Sure are a lotta extra parts on that board compared to an OCD or Alpha Drive.


Whatever kind of diodes these may be Mike Fuller wrote on Facebook that the Forward Voltage is 0,35 V.


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## ClassicFuzz (Sep 15, 2022)

I am still scratching my head. How would I wire a dpdt switch if I'd be using this layout from Effects Layouts? And where would I cut a trace?:


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## manfesto (Sep 15, 2022)

ClassicFuzz said:


> I am still scratching my head. How would I wire a dpdt switch if I'd be using this layout from Effects Layouts? And where would I cut a trace?: View attachment 32304


you wouldn't need to cut a trace, you'd use two of the pads of Q3 and Q4 since those are what you're modifying.
EDIT - I'm wrong and will rephrase once I find some paper


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## manfesto (Sep 15, 2022)

ClassicFuzz said:


> I am still scratching my head. How would I wire a dpdt switch if I'd be using this layout from Effects Layouts? And where would I cut a trace?: View attachment 32304


So here's one way to do it, although it takes four 2N7000s instead of two, which I'll figure out next, but this is basically how you'd do clipping mods where you just fly different sets of diodes on the DPDT switch itself


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## manfesto (Sep 15, 2022)

ClassicFuzz said:


> I am still scratching my head. How would I wire a dpdt switch if I'd be using this layout from Effects Layouts? And where would I cut a trace?: View attachment 32304


oh actually this way's much easier and I was overthinking it.

EDIT: the diodes are backwards in my drawing, my bad. Source should connect to the cathode of the D9K, not the anode!


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## Robert (Sep 15, 2022)




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## ClassicFuzz (Sep 15, 2022)

manfesto said:


> oh actually this way's much easier and I was overthinking it.
> 
> EDIT: the diodes are backwards in my drawing, my bad. Source should connect to the cathode of the D9K, not the anode!
> View attachment 32310


Nice, this looks good. With Q3 & Q5 "source" you mean DG-Pad?


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## manfesto (Sep 15, 2022)

ClassicFuzz said:


> Nice, this looks good. With Q3 & Q5 "source" you mean DG-Pad?


No I mean the actual S leg of the transistor, you'd solder in D and G, then bend the S leg up and solder a wire from it to the center lug of the DPDT switch.

EDIT: also from the EffectsLayout layout, it's Q3 and Q4, not Q5


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## ClassicFuzz (Sep 15, 2022)

manfesto said:


> No I mean the actual S leg of the transistor, you'd solder in D and G, then bend the S leg up and solder a wire from it to the center lug of the DPDT switch.
> 
> EDIT: also from the EffectsLayout layout, it's Q3 and Q4, not Q5


My mistake, I meant Q4 and wrote Q5 

Like this?:


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## manfesto (Sep 15, 2022)

ClassicFuzz said:


> My mistake, I meant Q4 and wrote Q5
> 
> Like this?: View attachment 32313


not quite, you won't be touching the "G" pads at all (or rather, you'd solder the "D" and "G" like normal into the board).

You won't solder the "S" legs into the board, instead you'll bend them up and solder wires from them to the center lugs of the DPDT switch.

Then the "S" pads on the board will be wired to the bottom lugs of the DPDT switch.

Both diodes will be facing the same way, with their cathodes attached to the top lugs of the DPDT switch.


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## ClassicFuzz (Sep 15, 2022)

manfesto said:


> not quite, you won't be touching the "G" pads at all (or rather, you'd solder the "D" and "G" like normal into the board).
> 
> You won't solder the "S" legs into the board, instead you'll bend them up and solder wires from them to the center lugs of the DPDT switch.
> 
> ...


Ok, now I understand. Thanks


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## mdc (Sep 15, 2022)

Big Monk said:


> oftentimes there is only a thin layer of bullshit between that $200 pedal and the one you make in your basement for $40.



That layer could generally be called "valuing your labour and someone else's R&D at $0/hr."


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## manfesto (Sep 15, 2022)

ClassicFuzz said:


> Ok, now I understand. Thanks
> 
> View attachment 32318


If you’re using D9 diodes that’s perfect, since the stripe is on the anode on those diodes and you want the cathodes connected to the top lugs

If you’re using 1N34s or others, the diodes will be flipped from that diagram wit the stripes pointing up, either way it’ll be good to test and double check


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## Big Monk (Sep 15, 2022)

mdc said:


> That layer could generally be called "valuing your labour and someone else's R&D at $0/hr."



True, but if our Chinese brethren are any indication, sometimes “R&D” is tweaking someone else’s R&D…😂


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## ClassicFuzz (Sep 16, 2022)

manfesto said:


> If you’re using D9 diodes that’s perfect, since the stripe is on the anode on those diodes and you want the cathodes connected to the top lugs
> 
> If you’re using 1N34s or others, the diodes will be flipped from that diagram wit the stripes pointing up, either way it’ll be good to test and double check


Just built it and it works. I used D9 diodes with the same voltage and it sounds the same. Thanks again for all your help.


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## Locrian99 (Sep 16, 2022)

I’ve got a clone of 1.4v I built (which is the version with the one germanium diode).   I decided to make a switch on mine to take bypass the diode.   I feel like I wasted the switch, the difference is very subtle, it’s there but it’s subtle.   I used a 1n34 for the germanium.   I also dinked around with doing an on off on with the 1n4148 again the difference is there but it’s so subtle I question the point. But hey the pedal looks cooler with an extra switch right.


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