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?

 

[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.

 

[music6000]

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!

 

[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.

 

[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.

 

[music6000]

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

 

[music6000]

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.

 

[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.

 

[music6000]

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.

 

[bobthebuilder]

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.

 

[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.

 

[music6000]

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

 

[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!

 

[Flipguitarist]

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.

 

[Chuck D. Bones]

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

 

[Flipguitarist]

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.

 

[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.

 

[zgrav]

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?

 

[Robert]

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.

 

[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.

 

[Flipguitarist]

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!