# Brown Betty trimpot/gain knob stuck between high gain and really high gain



## Kroars (Aug 13, 2021)

So, built two more Brown Betty’s one works great one works ok…. All components tested prior to install (except for IC’s). 

Problem:  On one of the two the trimpot doesn’t affect gain much at all.  Almost like it’s always full CW even when turning.  I can’t get that low gain level when the Gain knob is turned full CCW like I can with the others I’ve built.  The only real difference I’ve found is that on the good pedal the pins on IC’s are standard 9v on pin 8 and close to 4.5 on others.  On the bad one they’re all the same except for pin 7 on IC2 which reads 3.4v.

Also on C22 the good one goes from 4.498 to 4.489 and the bad one goes from 4.555 to 4.407 when adjusting trimpot.  Seems like a bit of a difference.

IC’s were changed from good one to bad one -same issue. Also replaced trimpot -same issue.

Anyone have an idea what to check next?

Thank you!!


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## Kroars (Aug 20, 2021)

Any ideas?


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## Feral Feline (Aug 20, 2021)

Kroars said:


> ... Almost like it’s always full CW even when turning.  I can’t get that low gain level when the Gain knob is turned full CCW like I can with the others I’ve built.




Maybe the trimpot is faulty, and if so it could be stuck wide open, no matter where you turn it.


I've been lucky and haven't had any faulty components yet, but there seems to be a surprising number of people here on the forum that have brand new parts (caps, pots, "legit" ICs, etc) that are faulty from the factory.


However, Pin 7 of IC2 suggests the problem may lie elsewhere. Have you checked all the resistor values leading to/away-from pin 7 IC2?


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## Kroars (Aug 21, 2021)

Feral Feline said:


> Maybe the trimpot is faulty, and if so it could be stuck wide open, no matter where you turn it.
> 
> 
> I've been lucky and haven't had any faulty components yet, but there seems to be a surprising number of people here on the forum that have brand new parts (caps, pots, "legit" ICs, etc) that are faulty from the factory.
> ...


I had replaced the trimpot already, no luck.  Im getting back from WA tomorrow and will double check values.  I eyeballed everything with the other board that works perfectly and everything seemed the same.


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## JamieJ (Aug 21, 2021)

It looks like you have 1k instead of 10k for R14. That is in series with the trimmer. That could explain the issue with the trimmer not behaving.

EDIT: I may have the colours wrong as it’s hard to tell if that 4th stripe is brown or red.


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## Loxton (Aug 21, 2021)

Are your electrolytic caps installed backwards? Or am I seeing things?


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## music6000 (Aug 21, 2021)

Loxton said:


> Are your electrolytic caps installed backwards? Or am I seeing things?


That's what I'm seeing, Electrolytics  are reversed!!!
Can you confirm R30 - 10 ohm = Brown, Black, Black, Gold, Brown & Trimmer is 104 =100K


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## Robert (Aug 21, 2021)

music6000 said:


> That's what I'm seeing, Electrolytics  are reversed!!!



Assuming this is the most recent revision of the board the electrolytics are probably correct.

Updated build doc just for clarity:  https://docs.pedalpcb.com/project/BrownBetty-PedalPCB.pdf


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## music6000 (Aug 21, 2021)

music6000 said:


> That's what I'm seeing, Electrolytics  are reversed!!!
> Can you confirm R30 - 10 ohm = Brown, Black, Black, Gold, Brown & Trimmer is 104 =100K


Do you have the clipping leds in the right way

Continuity test on trimmer to matching circles :


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## Kroars (Aug 22, 2021)

JamieJ said:


> It looks like you have 1k instead of 10k for R14. That is in series with the trimmer. That could explain the issue with the trimmer not behaving.
> 
> EDIT: I may have the colours wrong as it’s hard to tell if that 4th stripe is brown or red.


It’s a 10k.  I appreciate the help!


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## Kroars (Aug 22, 2021)

music6000 said:


> That's what I'm seeing, Electrolytics  are reversed!!!
> Can you confirm R30 - 10 ohm = Brown, Black, Black, Gold, Brown & Trimmer is 104 =100K


R30 is R100 on my board and yup it’s 10R. Trimmer is indeed 100k.  Thanks for the help!


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## Kroars (Aug 22, 2021)

music6000 said:


> Do you have the clipping leds in the right way
> 
> Continuity test on trimmer to matching circles :
> View attachment 15108


Continuity looks good.  I suppose it’s a possibility I put the led’s in the wrong way.  I’m fairly certain they’re correct, but it’s a possibility.  Based on the issues I brought up with weird voltage only in IC2 and trimpot seemingly stuck between mid-hi gain -would you think pulling them out and putting new ones in would be the next reasonable step?

Update:

Played with it a bit more since arriving home late last night.  It almost seems now like it’s the Gain knob (pot) that doesn’t do much.  I can at least hear the gain hiss climb when turning the trimpot CW. The actual effect just stays at high gain.  Funny, I noticed the Gain potentiometer seems to have less of an affect on the effect than the trimpot.  Although putting a DMM on the gain pot it seems to work great.


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## music6000 (Aug 22, 2021)

With all knobs @ 12.00 O'clock & Gain knob at minimum there should be medium gain & as you increase clockwise you should hear a obvious rise in Volume & more Sustain all the way up to Max. rotation.
You used Cusack pots for Volume & Gain, ARE the Pot values right, Volume A50K , Gain A1M?
If the Clipping led's have a flat machined at the base, the pair should be facing opposite each other on each side!


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## Feral Feline (Aug 22, 2021)

Kroars said:


> ...I suppose it’s a possibility I put the led’s in the wrong way.



So long as the clipping LEDs within each set are _anti-parallel to each_, it won't matter:

>|
|<

👆
is the same as
👇
|<
>|

Whether going to VDD, or in the loop of IC2.2



The other clipping diodes in IC3.2's loop, D1–4, match the PCB's silkscreen, so no problem there so long as the soldering is good.


I know, I'm probably not telling you anything you don't already know...


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## Kroars (Aug 23, 2021)

music6000 said:


> With all knobs @ 12.00 O'clock & Gain knob at minimum there should be medium gain & as you increase clockwise you should hear a obvious rise in Volume & more Sustain all the way up to Max. rotation.
> You used Cusack pots for Volume & Gain, ARE the Pot values right, Volume A50K , Gain A1M?
> If the Clipping led's have a flat machined at the base, the pair should be facing opposite each other on each side!


They are.  Like I mentioned, I put a DMM on the pots and they read the same between the working one and the one in question.


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## music6000 (Aug 23, 2021)

Kroars said:


> They are.  Like I mentioned, I put a DMM on the pots and they read the same between the working one and the one in question.


Can you confirm R3, R7, R14, R101 are all 10k = Brown, Black, Black, Red, Brown ?


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## Kroars (Aug 23, 2021)

music6000 said:


> Can you confirm R3, R7, R14, R101 are all 10k = Brown, Black, Black, Red, Brown ?


Yep.  Individually tested prior to installation as well.  Both boards were in front of me, both exactly the same.  One works great, on the other the gain knob doesn’t seem to do anything at all.  LED’s got significantly brighter when turning the trimpot CW, but nothing with the gain knob.


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## music6000 (Aug 23, 2021)

Kroars said:


> Yep.  Individually tested prior to installation as well.  Both boards were in front of me, both exactly the same.  One works great, on the other the gain knob doesn’t seem to do anything at all.  LED’s got significantly brighter when turning the trimpot CW, but nothing with the gain knob.



Test For Continuity with matching Circles, If this is Good then you may have a dud Pot!!!
I hope you have a dud trace between Gain pot Legs 2 & 3!


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## Kroars (Aug 23, 2021)

music6000 said:


> Test For Continuity with matching Circles, If this is Good then you may have a dud Pot!!!
> I hope you have a dud trace between Gain pot Legs 2 & 3!
> 
> View attachment 15170


I’ll check those now and let you know.  Would the pot be bad if it reads the exact same as the good one while turning the knob and using a DMM?  Both pedals get identical readings on the gain pot.


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## Kroars (Aug 23, 2021)

music6000 said:


> Test For Continuity with matching Circles, If this is Good then you may have a dud Pot!!!
> I hope you have a dud trace between Gain pot Legs 2 & 3!
> 
> View attachment 15170


Ended up changing pot, because why not.  Same issue.  I have continuity between all points you outlined EXCEPT for anything between the pin 7 of IC1 and neither of the blue circles on the clipping LED nor the 1st leg of the gain pot you have circled blue.  I mean, I’ve had a damaged trace in one other board (out of over 300) you think that may be it?


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## Kroars (Aug 13, 2021)

So, built two more Brown Betty’s one works great one works ok…. All components tested prior to install (except for IC’s). 

Problem:  On one of the two the trimpot doesn’t affect gain much at all.  Almost like it’s always full CW even when turning.  I can’t get that low gain level when the Gain knob is turned full CCW like I can with the others I’ve built.  The only real difference I’ve found is that on the good pedal the pins on IC’s are standard 9v on pin 8 and close to 4.5 on others.  On the bad one they’re all the same except for pin 7 on IC2 which reads 3.4v.

Also on C22 the good one goes from 4.498 to 4.489 and the bad one goes from 4.555 to 4.407 when adjusting trimpot.  Seems like a bit of a difference.

IC’s were changed from good one to bad one -same issue. Also replaced trimpot -same issue.

Anyone have an idea what to check next?

Thank you!!


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## Robert (Aug 23, 2021)

Pin 7 of IC1 should have continuity to the Red circles in the pic above, not blue.

Turn your Gain pot to minimum and measure the resistance between pins 6 and 7 of IC1,   then turn the Gain pot to maximum and make that same measurement again.

You should go from around 22K (at minimum) to over 1M at maximum (or significantly higher than 22K, depending on the accuracy/impedance of your meter).


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## Kroars (Aug 23, 2021)

Robert said:


> Pin 7 of IC1 should have continuity to the Red circles in the pic above, not blue.
> 
> Turn your Gain pot to minimum and measure the resistance between pins 6 and 7 of IC1,   then turn the Gain pot to maximum and make that same measurement again.
> 
> You should go from around 22K (at minimum) to over 1M at maximum (or significantly higher than 22K, depending on the accuracy/impedance of your meter).


Thanks!! Double checked with the red circles and we have continuity to pin 7 on IC1.  In reference to measuring resistance of pins 6&7 of IC1 -what if my meter starts at 28M (gain pot minimum) and ends around 28M (maximum)? Got a fluke 115.

Do you know what would cause pins 6&7 to sit around 28M despite gain knob being changed from min to max?  I’ve already changed the pot out and tested it prior to installing, so it’s got to be something other than the pot.


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## music6000 (Aug 23, 2021)

I had Pin 7 & R9 CIrcles reversed, You should have Continuity between Gain 1 to L1 - K to L2 - A to R9!
This should be correct :


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## music6000 (Aug 24, 2021)

music6000 said:


> I had Pin 7 & R9 CIrcles reversed, You should have Continuity between Gain 1 to L1 - K to L2 - A to R9!
> This should be correct :
> View attachment 15190
> 
> View attachment 15194


Have you got Continuity between all the  Blue circles now?


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## Kroars (Aug 26, 2021)

music6000 said:


> Have you got Continuity between all the  Blue circles now?


Yup.  Just had a chance to re check.  Continuity on all circles you outlined.  This is driving me crazy.  It’s so strange.  Tons of gain and pedal sounds great, it’s just that the Gain pot has absolutely no effect on it.  I mistakenly mentioned the trimpot on the title, but I see now that it does affect it a bit (definitely makes the LED’s shine brighter when turned up).  Just seems the Gain knob does absolutely nothing.

At this point I’ve replaced the trimpot, the A1M Gain pot as well as L1 & L2.  Maybe I should try replacing L3 & L4?  I’m at a complete loss on this.  Never came across an issue like this where everything works great except for one potentiometer.


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## music6000 (Aug 26, 2021)

Are you positive you have Continuity between Leg *2 & 3 *Pads on the Gain pot, there is a Trace between them?


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## Kroars (Aug 26, 2021)

music6000 said:


> Are you positive you have Continuity between Leg *2 & 3 *Pads on the Gain pot, there is a Trace between them?
> 
> View attachment 15282


Ok, now I don’t have continuity between red circles on gain pot and red circles on L 1 or 2……. I don’t know if I somehow missed that before or if it’s intermittent.  Although I definitely do not have continuity there.

Im guessing the fix would be a jumper between the pot and L-1?  Thanks again for your patience and help!!

Edit: now I have continuity!   Thank you again, pedal works as it should now.  You’re awesome!!


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## music6000 (Aug 26, 2021)

Kroars said:


> Ok, now I don’t have continuity between red circles on gain pot and red circles on L 1 or 2……. I don’t know if I somehow missed that before or if it’s intermittent.  Although I definitely do not have continuity there.
> 
> Im guessing the fix would be a jumper between the pot and L-1?  Thanks again for your patience and help!!
> 
> Edit: now I have continuity!   Thank you again, pedal works as it should now.  You’re awesome!!


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