# Distortion 250 Gain Pot Issue



## D1chotomy (May 21, 2020)

I just built the Distortion 250 and it works. Mostly. I had to change a couple values due to not having a few components on hand. I did not have a 47nF for C3, so I used a .082uF in place. Secondly, I used 1N4148 diodes. My issue is that the pedal works, but the taper on the volume control is not working properly. I get almost no gain what so ever until I hit the max position. Then it's full on gain. Is my choice of cap in C3 the issue or is it the diodes? 

Thanks for your help.


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## benny_profane (May 21, 2020)

Reposting from the other thread:

Increasing C3 from 47nF to 82nF reduces the HPF corner from 720Hz to 413Hz with gain at max and 1.9Hz at gain min (assuming you have a 1M potentiometer).

Fc_max = 1/(2*π*(4700+0)*(.082)) = 413Hz
Fc_min = 1/(2*π*(4700+1000000)*(.082)) = 1.9Hz

Since the purpose of that is to mitigate op amp instability, I don't think that's where your problem is. You might consider looking at a C-taper pot (the DOD 250 uses a C500k pot instead of a B1M used in the Distortion+)

Also, if you want to preserve the original frequency response and you have more 82nF caps, try a series arrangement:

C_total = (C1*C2)/(C1+C2)
C_total = (.082*.082)/(.082+.082)
C_total = .041 => *41nF*

It won't be quite the same, but it'll be closer.


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## D1chotomy (May 21, 2020)

benny_profane said:


> Reposting from the other thread:
> 
> Increasing C3 from 47nF to 82nF reduces the HPF corner from 720Hz to 413Hz with gain at max and 1.9Hz at gain min (assuming you have a 1M potentiometer).
> 
> ...




Thanks for taking the time to write that up. I found a .56nF value cap, so I threw that in there thinking it'd be a bit closer. It is better now, but still not quite there. There's a little more range in the gain pot, but still not much until you get to that final bit.

So, I want to understand what you meant here. Are you saying that I could change C1, C2 and C3 to 82nF and I would arrive at 41nF? Sorry, I'm still pretty new to the "how's an why's" of all of this. I am trying though.


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## zgrav (May 21, 2020)

this is just about c3, or what gets connected to the two holes on the pcb where c3 is supposed to go.

putting 2 of the 82N caps in series to replace the one capacitor turns them into the equivalent of  41n cap.


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## benny_profane (May 21, 2020)

No problem. And @zgrav is right. Sorry about the confusion.

To be clear, you're talking about the gain pot and not the level pot, right? What values do you have for each? I think you're having an issue with the taper more than anything. The HPF formed with C3 changes the tonal character of the signal (and helps stabilize the op amp when it's pushed), but it shouldn't have a 'bunching up' affect on the sweep of the gain pot.


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## D1chotomy (May 21, 2020)

zgrav said:


> this is just about c3, or what gets connected to the two holes on the pcb where c3 is supposed to go.
> 
> putting 2 of the 82N caps in series to replace the one capacitor turns them into the equivalent of  41n cap.



This makes more sense now. My question was dumb!


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## D1chotomy (May 21, 2020)

benny_profane said:


> No problem. And @zgrav is right. Sorry about the confusion.
> 
> To be clear, you're talking about the gain pot and not the level pot, right? What values do you have for each? I think you're having an issue with the taper more than anything. The HPF formed with C3 changes the tonal character of the signal (and helps stabilize the op amp when it's pushed), but it shouldn't have a 'bunching up' affect on the sweep of the gain pot.



Hi there.  Yes, I am talking about the gain pot. I used what the build guide had laid out, a B1M. I will double check that, but I'm nearly positive that's what I used.

Now, on the LEVEL pot, I had to use an A100k as it's all I had. It has a smooth taper, but the volume does seem a bit low.


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## D1chotomy (May 27, 2020)

Switched out the gain pot for a C100k at the advice of @benny_profane and it now works more like it should. Thanks for the help here. I posted a build report, but my art kinda sucks.


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## benny_profane (May 27, 2020)

Nice work! Glad to hear you got it sorted out!


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## D1chotomy (May 27, 2020)

benny_profane said:


> Nice work! Glad to hear you got it sorted out!



Yeah man, you were right.


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## Untro (Dec 3, 2020)

I'm having the same issue with this pedal, Ill try popping a c100k in there instead! I have c2 in a socket, but maybe I'll mess with c3 in the interim. Sounds great when its all the way up! but the potentiometer is basically for show.


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