# Nugget fuzz issues



## brandonmarsella (Jun 21, 2021)

Hey I just finished my nugget fuzz built but some things seem off. I double checked all my components and joints. The transistors seem to be getting the right voltages and the diodes seem to read just about .3 for forward voltage.  

I get a whine or squeal from the pedal with the bias turned up. This happens even with drive and sustain turned down (I saw in another post this was expected with the drive up).

Also with the pedal only really sounds like the demos with the drive and sustain all the way up. Rolling either back at all doesn't seem to match the online demos. 

Anyone else have this issue?


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## Chuck D. Bones (Jun 21, 2021)

It makes no sense to turn the Bias trim all the way up.  

The 1N34A diodes need to be low leakage to get any gain out of this circuit.  Good luck finding low-leakage germanium diodes; they are few and far between.  I suggest socketing D1 & D2 and replacing the Big Green Hulk you're using for C5 with something the right size so you can access the sockets.  If you know how to measure diode leakage, then you can test them before you install.  You can also try BAT-41s for D1 & D2.  They're Schottky, not germanium, but at least the circuit will work.


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## brandonmarsella (Jun 22, 2021)

Hey thanks!

I'll try playing around with the diodes. What leakage should I shoot for?

Also in this demo the pedal doesn't whine with the bias knob fully open: 




Could the whine be related to the diodes? Maybe the ng-3 uses a different pot value?


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## Betty Wont (Jun 22, 2021)

I made the Bias control an external pot on my Nugget build and it does not squeal. The full range of the Bias control should be useful.


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## Kroars (Jun 22, 2021)

brandonmarsella said:


> Hey thanks!
> 
> I'll try playing around with the diodes. What leakage should I shoot for?
> 
> ...


I had the same issue trying to find low leakage diodes.  The only ones I had consistently found that were low leakage were 1n695’s (I went through 100 Ge diodes of all kinds that didn’t pass the test).  Most 1n695’s I tested were between 1M-6M ohms, perhaps it was just a good batch but that was my experience.  I believe you’re looking for at least or as close to 1M ohms.   Just in case, the way you test is to set your DMM to 6M ohms (manual range, not auto range) and test with your red probe on the cathode and black probe on the anode.  Chuck helped me with this on the same circuit (Thanks Chuck!).


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## Chuck D. Bones (Jun 22, 2021)

Betty Wont said:


> I made the Bias control an external pot on my Nugget build and it does not squeal. The full range of the Bias control should be useful.


The signal will die if you turn BIAS full clockwise because it shorts the signal to Vcc.



brandonmarsella said:


> I'll try playing around with the diodes. What leakage should I shoot for?


As low as possible.  If they measure 500K or higher resistance, they should work.



brandonmarsella said:


> Could the whine be related to the diodes? Maybe the ng-3 uses a different pot value?


This circuit has a lot of gain, so the whine could be power supply noise (try a battery) or stray coupling.  Show us your off-board wiring.

Who has an accurate NG-3 schematic?  I've read that the NG-3 is an NG-2 with the bias pot on the front panel, but seen no evidence to back that up.  A trace or photos of a Cornish unit would be helpful.


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## Betty Wont (Jun 22, 2021)

From Pere Cornish website: "Variable BIAS Control: Class A setting is with BIAS fully clockwise; Class B is approximately 12 o'clock and Class C fully anti-clockwise."
This is how mine works. He also states that the stock ng-2 bias setting is about 2/3 up, calibrated against the db of the noise floor.


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## brandonmarsella (Jun 22, 2021)

Chuck D. Bones said:


> The signal will die if you turn BIAS full clockwise because it shorts the signal to Vcc.
> 
> 
> As low as possible.  If they measure 500K or higher resistance, they should work.
> ...


Seems like the whine is related to the power supply. Sorry I should have thought of that. I always test my pedals with the same snark power supply on my bench and never had issues. This circuit seems to not like it though. Testing with a battery and a different supply the whine goes away! Great suggestion.

I'll play with some diode combos this week and report back what I find.


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## Chuck D. Bones (Jun 22, 2021)

Makes me think there is a resistor or trimmer in series with the external pot.  BTW, the "Class A, Class B, Class C" stuff is purely notional because this circuit is not capable of class B operation.


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## brandonmarsella (Jun 22, 2021)

Chuck D. Bones said:


> Makes me think there is a resistor or trimmer in series with the external pot.  BTW, the "Class A, Class B, Class C" stuff is purely notional because this circuit is not capable of class B operation.


I've read there is a resistor in series. I didn't bother with that though because I don't mind it going full off in some settings.


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## fig (Jun 22, 2021)

Would that mean that the bias pot does not reach Vcc when dimed?


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## Chuck D. Bones (Jun 22, 2021)

Going by this Vero layout:
https://vero-p2p.blogspot.com/2020/10/pete-cornish-ng-3-fuzz-vero-layout.html
Cornish put a 4.7K resistor in series with the B50K BIAS pot.


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## Robert (Jun 22, 2021)

I believe that is just a work-alike someone put together using the Nugget schematic.

Yep.

_"As I've never seen a schematic for the NG-3, this is my work-a-like."_


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## Robert (Jun 22, 2021)

I know someone who has an NG-3, but I _don't_ know if I can get my hands on it...

I suspect they'd become a bit anxious when I brought out the hot air and scalpel.


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## brandonmarsella (Jun 23, 2021)

Ok so here's the verdict. I ended up socketing the diodes. I found one Ge diode that read around 700k and another right around 1M. The circuit sounded pretty good. I didn't have any BAT-41s but I had some 46s, which measured around 6M. I swapped back and forth a few times and ultimately liked the BATs more. The fuzz just sounded sharper to me, if that makes sense. All in all, I REALLY like the pedal now. 

Thanks for the help everyone!


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## Chuck D. Bones (Jun 23, 2021)

Cool. Glad you got it sorted out.  
All this talk about germanium leakage and how it affects circuit performance has prompted me to write an article on the topic.  It's "mostly done" but you know how that goes.  Probably won't get it published until the weekend.


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## Robert (Jun 28, 2021)

Cornish NG-3 incoming.


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## Chuck D. Bones (Jun 28, 2021)

Chuck D. Bones said:


> All this talk about germanium leakage and how it affects circuit performance has prompted me to write an article on the topic.  It's "mostly done" but you know how that goes.  Probably won't get it published until the weekend.


It's done, you can find the article in Chucks Boneyard.


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## palelight (Jul 8, 2021)

Robert said:


> Cornish NG-3 incoming.


Psyched for this. Would an updated PCB have the buffer integrated as well?


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## andy-h-h (Oct 12, 2021)

Robert said:


> I believe that is just a work-alike someone put together using the Nugget schematic.
> 
> Yep.
> 
> _"As I've never seen a schematic for the NG-3, this is my work-a-like."_


I just saw this thread - yes that would be me.   It does work pretty well, and I used a 4.7k as that was at the end of the range where the transistor started to cut out and not work.  I've also used a 25k pot instead of a 50k for a more useful range (to my taste anyway).

 I'm looking forward to seeing an actual schematic when this eventually comes out.


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