Angry Charlie noise

mimosa

New member
I made my own angry charlie, including PCB layout. Mostly using SMD components. It works well, however it does generate a fair amount of noise when engaged and was wondering if it's because of my layout or if this pedal does generate lots of noise due to the nature of the circuit. My PCB has 4 layers, all power paths are on the bottom layer, then ground plane, and all signal path on the top 2 layers, with minimal path crossing. All my capacitors are either film (through holes) or C0G class 1 if ceramic SMD to avoid microphonic effects of class 2 ceramic caps. The power filtering is on a separate PCB on the footswitch, also to avoid noise. So I am a bit puzzled in how I can minimize the noise to a more normal level. I was also careful in the integration to avoid ground loops and signal wires near power wires.
 
I only ever design two layer boards but I place a ground pour on both layers which can reduce cross talk between traces. That could be causing your issue.

Have you also ruled out it’s not your power supply? Try it with a battery only if you can.

We’d need to see pictures of the board and schematic to make a more informed decision.
 
Where have you grounded the circuit? You are using insulated jacks which don’t connect to the enclosure. I would run a wire from a ground point and touch it to the enclosure and see if that makes the noise go away.
 
I don't have soldered connection for ground on the enclosure, because my potentiometer have their body soldered to ground on the PCB and they are touching the enclosure directly. Continuity test between a ground point and the enclosure shows continuity
 
Just a thought a continuity is tested with 1.5 volts. Shielding should do the job with mV. You should measure the resistance.
I learned it the hard way. My shielding on a strat did beep, but didn't shield good enough.
 
Another possibility is my bias voltage is simply using a voltage divider from Vcc. But I've seen on the Angry Charles design it uses a TL072 in the power section instead. Perhaps the op-amp supplies more current to the bias voltage compared to using a resistor divider. Otherwise I am not sure why it would require an op-amp to supply the bias voltage; anybody knows? Would this be the source of my buzz?
 
on a breadboard, the TL072 as configured in the Angry Charles does provide indeed 4.5V. Normal since there are no gain in the configuration. The question is, does it matter? The only thing I could see is it would allow the LM833 to pull more current from the 4.5V on the + input leg of the second gain stage but I am not sure it is required. If it's just a reference voltage.. why using the TL072 to supply the 4.5V?
 
I think they just took advantage of an unused opamp stage... It doesn't hurt, but probably isn't necessary.

I've never noticed that the LM833 minimum voltage is listed at 10V, that's interesting, but there are quite a few 9V pedals that use them so I doubt that's the issue.
 
I think JHS has used the LM833 in a few designs, but my gut says it’s not the issue. I just plunked an LM833 into a Tube Screamer and it never sounded better.

Have you tried running your pedal off battery to see if it makes any difference?
 
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