Fuzz Foundry Deluxe - Schematic Error: Reverse Biased Electrolytics

M

mxnhlt

New member
Build Rating
4.00 star(s)
Noticed unexpected gating behavior in the 1uF/10uF "Fat" switch settings; I believe the printed polarization ends up reverse biasing the electrolytics. Decided to flip them and the gating is gone, 10uF instead has a sag effect where the noise floor takes a second to come back in. Probably should put new ones in instead. Could use a board revision or a build doc update.
 
Not saying you're wrong, but this is the first time I've heard of anyone having this issue with the project.

mxnhlt said:
Noticed unexpected gating behavior in the 1uF/10uF "Fat" switch settings
Click to expand...
This sounds like normal behavior for the Fuzz Foundry.

mxnhlt said:
Decided to flip them and the gating is gone, 10uF instead has a sag effect where the noise floor takes a second to come back in.
Click to expand...
This sounds like the behavior of an electrolytic that is installed backwards.


I'll take a look.
 
The original gating behavior is with non-gated settings (no Comp, no Gate, full Drive & Stab) that goes away when switching to the film caps. Here's my sim, slightly different values but the DC bias ends up about the same:
1771781582489.png 1771781679961.png
Thanks Robert!
 
How is the bias affected by turning the Comp and Gate controls? (or leaky germaniums)

I'm wondering if non-polar caps might be the way to go here.

I've found a couple other "Fat Foundry*" schematics with electrolytics in the same orientation (which doesn't mean it's right), and a couple in the opposite orientation (which doesn't mean it's wrong).

The Tone Bender MKI has the capacitor oriented the other way around, but it's a positive ground circuit, so ...

Let's build one.

*I'm not allowed to say their name online but I'm screaming it out loud as we speak (No one said I couldn't say it in person) :ROFLMAO: :ROFLMAO:
 
Last edited:
OK, built one on the standard PCB because I didn't feel like fooling with the rotary / toggle switches.

In hindsight, I probably should have so I could switch capacitors on the fly, but this serve should it's purpose.

1771785772781.png
 
Swapped in back-to-back electrolytics, still has the sag effect instead of the gating. But I kind of liked the additional gating! Don't really want to stress a cap to get it though, and the standard way to achieve gating is close enough in sound.
 
OK, so here we go.... and this is a tricky one.

The cap is definitely reverse biased.

However, I have less gating with the capacitor installed as marked on the PCB. It has more oscillation and sounds closer to the original germanium version, even though I have 2N3906 installed.

I actually prefer it this way, but the fact that there is an audible difference tells me that we are probably throwing off the bias, and that's not right.

I also forgot how awesome the 'Factory is. Man, what a fantastic fuzz.
 
Now, as for correcting the issue...

Normally if it was a single value incorrect (considering there are quite a few in stock) I would mark it out on the PCB and make a note in the build doc.... but this involves installing a part backwards, and I'm just not OK with that...

So, time for a correction.

I'm also going to leave this one powered up for a day or two, then pull and measure the cap.... because I really like it better this way and at least two other similar projects orient the cap the same way.

... and that is why the issue hasn't been discovered until now.

Thank you for the report, I have refunded your payment as a token of appreciation.
 
Last edited:
I just happen to be building this right now and did a quick search to see if there were any issues. Can you tell me what exactly should be changed from the 7/17/25 build doc?
 
Interesting! Following... I have some 1uf and 10uf mlcc's... wondering if it would be "right" or "wrong" if I used those (signal path/mlcc stuff notwithstanding)... Seems like the very definition of "right" and "wrong" is also up in the air since they both seem to work! Curious to see what conclusion you come to, Robert..

mxnhlt said:
Decided to flip them and the gating is gone, 10uF instead has a sag effect where the noise floor takes a second to come back in.
Click to expand...
I've experienced this with both a Superfuzz and a Foxx Tone Machine...

Robert said:
This sounds like the behavior of an electrolytic that is installed backwards.
Click to expand...
Huh... the SF and FTM mentioned above didn't have anything installed backwards - maybe it also happens on octave-up circuits sometimes? Not to derail...
 
Funkbone said:
I just happen to be building this right now and did a quick search to see if there were any issues. Can you tell me what exactly should be changed from the 7/17/25 build doc?
Click to expand...

Install C2 and C14 opposite to the polarity indicated on the silkscreen.

It'll work either way, and you might prefer it as marked on the PCB, but technically it's not correct.

Glad you reminded me, this thing is still plugged in on the shelf. I need to check the cap soon.
 
But..... they're already on a switch. :ROFLMAO:


Can I put the switch on a switch in case I don't want them to be switchable anymore? ... right, but then someone is going to want that switch to be switchable... 😞
 
While you're at it I noticed on the layout Q5 is labeled Q6. Also any idea when the boards will be back in stock? I want to build a couple more of these
 
Fuzz Foundry Deluxe 7/17/25 snippet:
FUZZ FOUNDRY DELUXE 5 vs 6.png

Q5's surely smudged and looks like a 6, but on closer examination that's a 5 in the upper right, judging from the the shape of the "5" in C5 and "6" in R6 as well as C6. 🧐

Mind the "5" in R5 looks nothing like the "5" in C5 (and elsewhere on the full schematic). 🤷‍♂️

I should be troubleshooting one of my builds right now, not looking at the curvature of a font's numerals. 😸
No wonder I never get anything done, I'm too busy with impo(r)tent schtuff, life's burning quandaries. 😹
 
You must log in or register to reply here.
Back
Top