# Angry Charles Bass Pot



## bobthebuilder

Hey everyone - new pedal builder here.

I've recently built an angry charles and everything seems to work except the bass control. After 12 O'clock on the knob the volume cuts off suddenly. Before 12 O'clock the volume increases as the knob is turned CCW. I've given a preliminary look over all the solder joints, components, and correct orientation of the potentiometers, and nothing seems obviously out of order. Any thoughts on what could be causing this strange behavior?


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## phi1

Can't say for sure of course, but it almost sounds like pin 2 of the bass pot is grounded... For troubleshooting, it's nice that you have the issue isolated to one area of the circuit.  Try to follow the schematic in that area and determine if all the bass pot pins and surrounding components are connected to the right place, and not going somewhere they shouldn't (use a multi-meter to check continuity). 

You could try to post some clear close-up pics, which might allow someone to see if there appears to be a mistake.

If it gets to the point that you need to de-solder components, I recently saw some tips about desoldering on the build reports - Chela Overdrive thread that might be helpful.


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## bobthebuilder

Thank you for the help,

I will investigate tomorrow and post the results.


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## bobthebuilder




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## bobthebuilder

Finally got some time to take a few pictures. Nothing seems to be grounding out, so I'm not sure what the best next step is. Anything look like it might be the culprit?


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## phi1

Wish I could help, I took a look at your pics and nothing jumped out. If it were me I'd start with a multimeter and check for continuity between all the connections surrounding that bass knob, checking the resistance of those resistors, as well as the resistance across the pot lugs.


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## bobthebuilder

Sounds good - I've checked the resistance of the pot and it seems to be correct so now I'll start with the PCB


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## bobthebuilder

Can I get some advice on how to check the voltages on the 2 IC's (TL072, LM833)?


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## zgrav

I would ground the black lead on your DMM to something grounded to your board like the sleeve on the audio in or auido out jack, set the DMM to volts, and go ahead and record the voltage on all the pins on the ICs and let's see what you get.


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## zgrav

also -- since you are running wires to your pots, make sure the three connections are correct for your bass pot (middle lug connects to R15 and then goest to IC2, pin 2, etc)


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## bobthebuilder

I hope these sketches are legible. My multimeter is analog and probably not very accurate so I'm not sure how helpful these results are.

The second picture represents the paths I've traced and verified that they are connected.

The resistance values for the bass pot between lugs 2 and 3 vary from 0-15k. Zero resistance when the knob is turned fully CW.


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## zgrav

To confirm -- the mid and treble pots work for their full range.
Bass pot works until the rotation is about halfway.  Then does all of the sound stop when you rotate past that point?  Or do you lose the bass but everything else is still working?  I read your question as saying all the sound stops at that point and not just the bass.

turn the treble and mid controls up all the way, and then turn the bass pot up to the point where the sound stops.  what happens if you then turn down the mid and treble?  nothing?  or does the sound come back?  I'm asking to see if there is a chance that the input on the IC is messing up somehow if the signal level gets "too high"     

Can you swap out another TL072 chip and see if it makes a difference?


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## bobthebuilder

Mid and treble work for their full range.  Their position does not affect when the bass pot cuts out.  For example, when they are both cranked, the bass pot cuts sound at around 2 O'clock.  When the mid and treble are turned down, the bass pot still cuts sound at the same position. 

(Mid and treble both increase volume as they are turned up and decrease volume as they are turned down.  I'm not sure if that is normal behavior for this pedal.)

Volume and gain pots work as expected.

Bass pot acts like a reverse volume control up until 2 O'clock when it rapidly cuts the output sound to barely audible volume.  From 2 O'clock to fully CW, I don't notice anything changing at all.  The bass pot increases the volume dramatically when it is fully CCW.

It seems that all the EQ controls feed into the same pin on IC2 so it seems strange that only the bass control is having problems.  I don't have another TL072 to swap, unfortunately.

If C13 was damaged, or if the bass bot was faulty, could this behavior be attributed to that?


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## zgrav

Maybe you are describing a linear pot for bass that is wired in "backwards" since you describe it as a reverse volume control.  when you note the volume changes dramatically at one end, that could be because it is a linear taper and if you used an audio taper it would give you more control over changes in sound level at that end.

So long as mid and treb are not also configured as reverse volume controls, I would swap the wires on the 1 and 3 lugs on the bass pot to also make it perform like a normal volume control.     The build doc calls for a 25K linear taper pot for the bass, and your pot could be an audio taper that would have exaggerated what was happening at each end or the rotation.  After you switch the wires, see if it changes the behavior you were hearing.  If it is a linear pot you will have changed the direction of the control but the effects at each end will still be the same.  If it was an audio taper pot, you will probably have more control over the part of the range that previously had the dramatic volume change.


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## bobthebuilder

I swapped the wires on the 1 and lugs on the bass pot and it behaves like a linear pot, basically the control is exactly reversed from before.

I'm not sure where to go from here. I'm confused because the mid and treble pots both work, yet everything feeds into pin 2 on the TL072. This makes me think that the IC is okay. The resistor values in the bass control circuit are continuous and they read the correct values, so the only thing I can think of is C13. Any further help is appreciated!


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## zgrav

I was wondering if your bass pot is bad, but that does not seem to be the case.   when you turn the bass knob, does it only affect the volume?  or is it also increasing the bass as well as the volume?


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## music6000

Are the Tantalum Capacitors ( C10, C11, C16) facing the Right way?


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## zgrav

I came across this article by R.G. Keen (a legend in the DIY community) about some trouble he had isolating a problem in the tone controls for a tube  amp that reminded me of this forum thread.  https://www.premierguitar.com/articles/troubleshooting-tube-amps-1   He finally attributed the problem to an "invisible short" on the circuit board. Check it out.


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## bobthebuilder

I can't really tell if the bass is being affected because the volume adjustment is so dramatic. I will look at that article, sounds like it will be a good read, thanks!

I will check the orientation of the capacitors, that would be a nice easy fix if that turns out to be the problem!


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## Robert

Can you measure the resistance between lug 2 of the Bass pot and pin 3 of the upper opamp? (TL072)


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## bobthebuilder

Hey everyone - new pedal builder here.

I've recently built an angry charles and everything seems to work except the bass control. After 12 O'clock on the knob the volume cuts off suddenly. Before 12 O'clock the volume increases as the knob is turned CCW. I've given a preliminary look over all the solder joints, components, and correct orientation of the potentiometers, and nothing seems obviously out of order. Any thoughts on what could be causing this strange behavior?


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## bobthebuilder

All the tantalum caps are in the correct orientation.

Resistance between lug 2 of the bass pot and pin 3 of TL072 is reading as infinite. It's a bit strange though: the R value starts at at a positive value then quickly rises to infinite.


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## music6000

bobthebuilder said:


> All the tantalum caps are in the correct orientation.
> 
> Resistance between lug 2 of the bass pot and pin 3 of TL072 is reading as infinite. It's a bit strange though: the R value starts at at a positive value then quickly rises to infinite.


Can you check R14-6K8 & R15-68K to make sure their not reversed.

 Resistor Calculator : http://resistor.cherryjourney.pt/
 Click on ''Bands'' for 4 or 5 Bands.

 Might be worth checking all the other Resistors!


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## zgrav

what is the resistance between lug 2 of the bass pot and PIN 2 of IC2 (TL072)?  Since PIN 3 connects to power, not to the tone pot, it is not surprising that there is little if any connectivity with lug 2 of the bass pot.  

using your DMM, make sure that lug 2 connects to C15, and that C15 connects to pin 2 on IC2.

Here is how to go through the other parts of the tone circuit.  If you look at the circuit in the build document you will see how the tone controls provide two different ways for the audio signal coming out of C12 to get to IC2.  The three controls all change the amount of the signal that gets filtered for the Bass, Mid, and Treb to connect to PIN 1 or PIN 2 on the TL072.   ---  so you can check the following for connectivity with your DMM and with an audio probe at these points:

going into the tone part of the circuit, make sure that  R12, R16 and LUG 3 of the Treble pot connect to each other and to C12.

then make sure that LUG 1 of Treble pot, R13, and R14 all connect to each other and also to PIN 1 of the TL072.

make sure that R18, R17 and R15 all connect to each other and also to PIN 2 of the TL072.

if all of that checks out,  make sure nothing in the bass path is shorting to ground (check R12, R14, R15, C14 and each lug on the bass pot).  also check those part values again to make sure they are right.


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## bobthebuilder

I checked, and R14 and 15 are not switched. The resistance is 68k between lug 2 of the bass pot and PIN 2 of IC2. 


_using your DMM, make sure that lug 2 connects to C15, and that C15 connects to pin 2 on IC2. _*CHECK*
_
Here is how to go through the other parts of the tone circuit. If you look at the circuit in the build document you will see how the tone controls provide two different ways for the audio signal coming out of C12 to get to IC2. The three controls all change the amount of the signal that gets filtered for the Bass, Mid, and Treb to connect to PIN 1 or PIN 2 on the TL072. --- so you can check the following for connectivity with your DMM and with an audio probe at these points: _**thank you for the explanation!*
_
going into the tone part of the circuit, make sure that R12, R16 and LUG 3 of the Treble pot connect to each other and to C12. _*CHECK*
_
then make sure that LUG 1 of Treble pot, R13, and R14 all connect to each other and also to PIN 1 of the TL072. _*CHECK*
_
make sure that R18, R17 and R15 all connect to each other and also to PIN 2 of the TL072. _*CHECK*
_
if all of that checks out, make sure nothing in the bass path is shorting to ground (check R12, R14, R15, C14 and each lug on the bass pot). also check those part values again to make sure they are right. _*CHECK *R12 and R14 are measuring as 6k, when they should be 6k8*


I went over all the resistors and they all measure correctly except R12/14 which are 6k, instead of 6k8. They share the same color pattern as R19, which measures correctly as 6k8.


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## music6000

bobthebuilder said:


> I checked, and R14 and 15 are not switched. The resistance is 68k between lug 2 of the bass pot and PIN 2 of IC2.
> 
> 
> _using your DMM, make sure that lug 2 connects to C15, and that C15 connects to pin 2 on IC2. _*CHECK*
> 
> _Here is how to go through the other parts of the tone circuit. If you look at the circuit in the build document you will see how the tone controls provide two different ways for the audio signal coming out of C12 to get to IC2. The three controls all change the amount of the signal that gets filtered for the Bass, Mid, and Treb to connect to PIN 1 or PIN 2 on the TL072. --- so you can check the following for connectivity with your DMM and with an audio probe at these points: _**thank you for the explanation!*
> 
> _going into the tone part of the circuit, make sure that R12, R16 and LUG 3 of the Treble pot connect to each other and to C12. _*CHECK*
> 
> _then make sure that LUG 1 of Treble pot, R13, and R14 all connect to each other and also to PIN 1 of the TL072. _*CHECK*
> 
> _make sure that R18, R17 and R15 all connect to each other and also to PIN 2 of the TL072. _*CHECK*
> 
> _if all of that checks out, make sure nothing in the bass path is shorting to ground (check R12, R14, R15, C14 and each lug on the bass pot). also check those part values again to make sure they are right. _*CHECK *R12 and R14 are measuring as 6k, when they should be 6k8*
> 
> 
> I went over all the resistors and they all measure correctly except R12/14 which are 6k, instead of 6k8. They share the same color pattern as R19, which measures correctly as 6k8.



Example: 
Blue, Black, Black, Brown, Purple (+ - 0.1%) = 6K
Blue, Grey, Black, Brown, Purple  (+ - 0.1%) = 6K8

*You need to change R12 & R14 to 6K8*


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## music6000

music6000 said:


> Example:
> Blue, Black, Black, Brown, Purple (+ - 0.1%) = 6K
> Blue, Grey, Black, Brown, Purple  (+ - 0.1%) = 6K8
> 
> *You need to change R12 & R14 to 6K8 ?????????????????*


 I just studied your PCB and all the Resistors appear to be the Correct Colour Bands so if the Resistors are from the same Batch they should be Correct.
As I have stated in another Post, I don't know the Resistors by Colour Bands, I used the Resistor Calculator for this Post.
I measure every Resistor, Cap, Potentiometer with a DMM.  Every Transistor, Diode, Led with a Peak DCA55.
I Socket every Op Amp.
This minimizes the loaded PCB being Faulty at the end of a Build.

Can you confirm that all your Pots are wired Correctly, When all the Fly leads are the same Colour, It multiplies the chance of Crossing them.


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## bobthebuilder

I can confirm that all the pots are wired correctly. I think next time I will use PCB mounted pots to make everything easier!

This is very interesting because the pedal seems to be working perfectly except for the response from the bass pot, but I can't seem to find anything wrong with the bass or tone section of the circuit! There may be some invisible short that I'm not finding, as zgrav alluded to with the premier guitar article. Also, I could just be missing something obvious due to my lack of knowledge in electronics.


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## music6000

bobthebuilder said:


> I can confirm that all the pots are wired correctly. I think next time I will use PCB mounted pots to make everything easier!
> 
> This is very interesting because the pedal seems to be working perfectly except for the response from the bass pot, but I can't seem to find anything wrong with the bass or tone section of the circuit! There may be some invisible short that I'm not finding, as zgrav alluded to with the premier guitar article. Also, I could just be missing something obvious due to my lack of knowledge in electronics.


Check and make sure Bass Pot Lug Board is not Cracked or Loose
Can you confirm Continuity between Bass Pot Legs & PCB Bass Pot pads.
Confirm you a re getting Variable resistance by measuring Bass Pot Lugs 1 & 2, 2 & 3, while adjusting Bass Pot.


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## bobthebuilder

music6000 said:


> Check and make sure Bass Pot Lug Board is not Cracked or Loose
> Can you confirm Continuity between Bass Pot Legs & PCB Bass Pot pads.
> Confirm you a re getting Variable resistance by measuring Bass Pot Lugs 1 & 2, 2 & 3, while adjusting Bass Pot.


Checked and appears to work correctly. I have ordered another B25k pot to wire up and see what happens, but the pot seems to be in working order from my testing.


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## zgrav

since you said that the bass control acts more like a volume control, try changing the value of the capacitor in that part of the circuit to see if it makes a difference in the sound.  Maybe change c13 to  22n or 33n.


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## music6000

bobthebuilder said:


> Checked and appears to work correctly. I have ordered another B25k pot to wire up and see what happens, but the pot seems to be in working order from my testing.



Try what* zgrav *has suggested, maybe the C13 - 47nF cap has failed, Measure with DMM.
Remove the Cap & check Continuity between Bass Pot Lug 3 to Cap pad, Bass Pot Lug 1 to other Cap pad


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## bobthebuilder

I'm waiting for some caps so I can play with C13. Just wanted to say thanks for the continued help - I'll post an update when the parts get here. In the meantime, I just boxed up the pedal and it sounds fine without bass control. At this point, I'm more scientifically interested in this particular problem!


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## Flipguitarist

bobthebuilder said:


> Hey everyone - new pedal builder here.
> 
> I've recently built an angry charles and everything seems to work except the bass control. After 12 O'clock on the knob the volume cuts off suddenly. Before 12 O'clock the volume increases as the knob is turned CCW. I've given a preliminary look over all the solder joints, components, and correct orientation of the potentiometers, and nothing seems obviously out of order. Any thoughts on what could be causing this strange behavior?


I have the same issue on my build.


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## Chuck D. Bones

Please post a photo of the board.  Do you have a DMM?


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## Flipguitarist

Chuck D. Bones said:


> Please post a photo of the board.  Do you have a DMM?


Thanks for the reply. Here you go. And yes I have multimeter. new to building pedals. Already built the park wah and be-od/dirty Shirley with no issues.


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## Chuck D. Bones

Soldering looks good.  No IC sockets (that's good).  I can't read the capacitors, we'll assume they're all correct.
Looks like all of the pots are wired to the board rather than using PC pins, is that true?  If so, how is the board supported and are you sure that the board is not shorting to anything on the bottom side?
When you get a chance, set all of the controls to 0 (full CCW), power up the pedal and measure each pin on IC2 to ground.  Voltages should be (approx):

pin 1   4.5V
pin 2   4.5V
pin 3   4.5V
pin 4   0V
pin 5   4.5V
pin 6   4.5V
pin 7   4.5V
pin 8   9V

Now set the BASS control to 10 (full CW) and measure pins 1 & 2 again.  I'm thinking there might be a DC offset on the input side of the tone controls.  The BASS control is the only one of the three that is DC coupled.  If there is a DC offset, then turning the BASS control up could cause the output of IC2.1 (pin 1) to saturate.  
I believe that C12 is backwards on the schematic and on the board layout.  Electrolytic caps are leaky when you reverse-bias them and that's what I think is happening here.  They don't all leak the same amount, which could explain why some pedals have a problem and others don't.


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## zgrav

Chuck D. Bones said:


> I believe that C12 is backwards on the schematic and on the board layout.  Electrolytic caps are leaky when you reverse-bias them and that's what I think is happening here.  They don't all leak the same amount, which could explain why some pedals have a problem and others don't.



That is an interesting idea to explain the odd behavior for the bass pot.  If that turns out to be the case, I guess trying a different cap for C12 would be one fix.  Would adding another electro cap in series after C12 also work?


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## Robert

Chuck D. Bones said:


> I believe that C12 is backwards on the schematic and on the board layout.



That's a good observation.    Whether it's the issue or not, I don't see any reason it shouldn't be flipped around the other way.

I'll have to update the schematic and layout.   I'd be interested to hear if reversing the cap makes a difference.


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## Chuck D. Bones

The circuit should work correctly if C12 is turned around.  The left side of C12 is biased at 0VDC and swings up to +/- 1.6V or so, clamped by D2 & D3.  The right side of C12 is biased at Vref (+4.5VDC) and has the same AC swing as the left side.  Once C12 has been exposed to reverse voltage, it has probably been permanently damaged and should not be reused.  Install a new one.


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## Flipguitarist

Chuck D. Bones said:


> The circuit should work correctly if C12 is turned around.  The left side of C12 is biased at 0VDC and swings up to +/- 1.6V or so, clamped by D2 & D3.  The right side of C12 is biased at Vref (+4.5VDC) and has the same AC swing as the left side.  Once C12 has been exposed to reverse voltage, it has probably been permanently damaged and should not be reused.  Install a new one.


Not short as far as I can tell, there’s sound just the bass reacts like how the original poster mentioned. I’ll try reversing c12 if that works. Will update when I do. Thank you all for the help!


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## bobthebuilder

Hey everyone - new pedal builder here.

I've recently built an angry charles and everything seems to work except the bass control. After 12 O'clock on the knob the volume cuts off suddenly. Before 12 O'clock the volume increases as the knob is turned CCW. I've given a preliminary look over all the solder joints, components, and correct orientation of the potentiometers, and nothing seems obviously out of order. Any thoughts on what could be causing this strange behavior?


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## Flipguitarist

Chuck D. Bones said:


> The circuit should work correctly if C12 is turned around.  The left side of C12 is biased at 0VDC and swings up to +/- 1.6V or so, clamped by D2 & D3.  The right side of C12 is biased at Vref (+4.5VDC) and has the same AC swing as the left side.  Once C12 has been exposed to reverse voltage, it has probably been permanently damaged and should not be reused.  Install a new one.


*Update*
Removed and installed and reversed a new 2u2 on C12. It works as it should. You’re the man! Thanks a lot!


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## Flipguitarist

Robert said:


> That's a good observation.    Whether it's the issue or not, I don't see any reason it shouldn't be flipped around the other way.
> 
> I'll have to update the schematic and layout.   I'd be interested to hear if reversing the cap makes a difference.


Installed and reversed a new capacitor on C12, works perfect now.


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## bobthebuilder

This is very interesting, thanks for the further investigation. I'll try to reverse C12 and see if my results are the same.


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## Flipguitarist

bobthebuilder said:


> This is very interesting, thanks for the further investigation. I'll try to reverse C12 and see if my results are the same.


Good luck! Hope it works out. Let us know.


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## Chuck D. Bones

Don't put the old C12 back in.  If it's damaged, turning it around won't solve the problem.  Did you measure the voltages?


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## Mojo321

I have built three of these, and I haven't noticed any bass knob problem.  But I will check and have my friends check theirs.


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## Flipguitarist

Mojo321 said:


> I have built three of these, and I haven't noticed any bass knob problem.  But I will check and have my friends check theirs.


Like Chuck mentioned not all capacitors leak the same that’s why others didn’t have any issues. Installing a new capacitor the other way around fixed my issue.


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## Chuck D. Bones

Parts that are overstressed can fail immediately, someday, or never.  It's those "someday" failures that you have to worry about because they will happen at the most inconvenient times.


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## Flipguitarist

Chuck D. Bones said:


> Parts that are overstressed can fail immediately, someday, or never.  It's those "someday" failures that you have to worry about because they will happen at the most inconvenient times.


 I meant to say Chuck not Dave lol.


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## bobthebuilder

Finally got around to opening up the pedal and reversing the polarity of C12, as Chuck D. Bones suggested.  I can confirm that this solves the bass control problem.  It appears that the schematic is updated, so this issue should be resolved for future builders.  Thanks again to everyone!


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