# box and all - interesting behavior



## NSJ (Nov 19, 2021)

I just finished building box and all EQ pedal. While the pedal at reasonable settings shines, I see some weird stuff happening at extreme sweeps. 

This is what is going on- Any help or pointers for troubleshooting will be greatly appreciated  

Scenario: All knobs maxed it sounds exactly how it is supposed to. But if I turn MIDS CCW then I lose volume. The MIDS seems to work only for first 25% and last 25% of the sweep - pedal comes alive in these positions. Anything in between I lose volume -  sound drops significantly below unity robbing all the harmonics. While in this 'low volume state', if I pull TREBLE back a notch then pedal comes alive again. 
So the interaction between treble and mids pot is quirky. Anyone else see this? Anything jumps out to you all? I did double-check cap values.


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## NSJ (Nov 20, 2021)

Here are some pics. Sorry this is my first troubleshooting post so didn’t know what to do. Hope this helps me get some responses. 🤞


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## NSJ (Nov 20, 2021)

Hoping this one clearer than previous.


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## jeffwhitfield (Nov 20, 2021)

Could you post a pic of the bottom of the board? Might need to see the solder joints there.


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## NSJ (Nov 20, 2021)

Thanks for your response! Please see attached. Let me know if you’d like other angles or clarity in some spots. 

Btw I did try replacing the mids pot with alpha pot but same issue. Hence in the picture there is no mids pot.


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## NSJ (Nov 20, 2021)

It’s surprising coz the issue is not at min or max on the pot - it’s somewhere in between the sweep. I wonder what component would affect that. Let me know if I can get any voltages at any points.  Have you built one? Does yours work fine across the sweep?


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## NSJ (Nov 20, 2021)

I lied. Replacing the tayda pot for MID with alpha pot helped. 
I wonder if while replacing i cleaned up something that made it to work. I’ll try using this “apparently bad pot” in a different build and see if it’s me or the pot. I want to bet it is me.


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## NSJ (Nov 21, 2021)

The issue is still there. I double checked all caps and resistors. And solder blobs. I guess I’ll just build another one and see what happens. 

Although it is an extreme setting and no one would ever use it, I’m afraid if I end up selling it then it’d look bad if someone sweeps the knobs across full range.


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## PJS (Nov 22, 2021)

I own the original if you need voltage measurements etc.  It does use a single quad op amp instead of 2 doubles, but the result should be the same


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## NSJ (Nov 22, 2021)

That’d be really helpful! Thanks a bunch for your response. This has been bugging me a lot. I’ve had 8 successful PP builds (other than box and all eq) so far and never ran into something like this.

I was also hoping someone here who has the PP build could run the same knob sweep experiment and report back. Coz the knob positions I’m trying are kinda impractical. It’s an outstanding tone when in sweet spots.


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## PJS (Nov 24, 2021)

Sorry, it's taken a while.  With 9.15V supply, I am getting 8.2V supply on the IC.  the OP amp pins down the pins 1-7 side are sitting at 4.5V.  The pins on the other side are at 4.0 to 4.1V  Looking at the schematic I would be assuming that IC1 would be the one biased to 4.0v and IC2 would be at 4.5V.  Anything else you want me to look at just let me know.


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## NSJ (Nov 24, 2021)

Thanks a lot! Let me check it today.


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