High frequency, low volume whine when pedal is plugged into power

[airvian]

Hello there!
The pedal I built works completely fine, but there is a very high pitched beep when I plug the pedal into power. Does anyone have a clue what could be causing such a beeping noise? I have opened it up and it seems to change depending on how I position the wiring from the 9V input to the pcb so I suspect that is what is ultimately causing it. Would wrapping the power wires in some foil or wire maybe fix it?

[idy]

What pedal? High gain?
Any charge pumps?
Any other pedals (maybe digital or charge pump) in the signal chain?
What kind of power supply?
Beep implies a quick signal that "beeps" and is done. A "whine" or "tone" suggests that it is continuous.

[airvian]

What pedal? High gain?
Any charge pumps?
Any other pedals (maybe digital or charge pump) in the signal chain?
What kind of power supply?
Beep implies a quick signal that "beeps" and is done. A "whine" or "tone" suggests that it is continuous.

It is a Peavy Decade preamp circuit. And in that case it isn't a beep but a whine. It's a constant high pitch sound. It is independent of the other pedals in the chain, though it gets accentuated when I run a Fuzz into it. In the signal chain I'd also run a HX FX, but that doesn't affect the whine either. The power supply is an affordable gator cases one with several 9V and 18V outlets (it has never caused problems though).

[airvian]

What pedal? High gain?
Any charge pumps?
Any other pedals (maybe digital or charge pump) in the signal chain?
What kind of power supply?
Beep implies a quick signal that "beeps" and is done. A "whine" or "tone" suggests that it is continuous.

OK so i quickly soldered to gether some wiring to power the pedal from a 9V battery and it seems that when running it from a battery the humming/whining is gone... Would getting/putting together a higher quality isolated power supply fix it?

[Vivek]

Please post your schematic

Does your circuit need +24V ?

[PRR]

> running it from a battery the humming/whining is gone...

What is this power supply?

Lots of simple affordable supplies make clean power, you don't have to go crazy.

Usually. Couple weeks ago we lost radio reception in the house. Just massive buzz/static. I finally traced to (of course) what was new in the house that day: a Dell mini-laptop with external line-wart power supply. The instant I yanked the AC off the wart the crap stopped (the laptop still ran on battery, inoffensively, showing it wasn't the laptop). As it is a good brand wart (LITE-ON) with FCC Home rating, from 2009, I assume some crap-filter has died of old-age or abuse.

[idy]

It does have a charge pump. This is still on when using a battery, but maybe not "communicating" with the other pedals/power supply?

This is the power section:

[anotherjim]

Intermodulation of the pedal's IC3 switching frequency and PSU noise is producing heterodyne whine.

The schematic snippet shows no supply bypass capacitors from the raw DC input. At a minimum, repeat both C10 and C11 somewhere on the +9v supply after the D2 cathode.

[airvian]

> running it from a battery the humming/whining is gone...

What is this power supply?

Lots of simple affordable supplies make clean power, you don't have to go crazy.

Usually. Couple weeks ago we lost radio reception in the house. Just massive buzz/static. I finally traced to (of course) what was new in the house that day: a Dell mini-laptop with external line-wart power supply. The instant I yanked the AC off the wart the crap stopped (the laptop still ran on battery, inoffensively, showing it wasn't the laptop). As it is a good brand wart (LITE-ON) with FCC Home rating, from 2009, I assume some crap-filter has died of old-age or abuse.

The power supply is a gator G-BUS-8.

[airvian]

Intermodulation of the pedal's IC3 switching frequency and PSU noise is producing heterodyne whine.

The schematic snippet shows no supply bypass capacitors from the raw DC input. At a minimum, repeat both C10 and C11 somewhere on the +9v supply after the D2 cathode.

So you think putting two more caps in the circuit will get rid of the noise? Would it matter where I put them after D2?

[Vivek]

The 2 new power conditioning caps should be physically as close to the Charge Pump IC as possible.

Many times, a ferrite bead in series with D2 also helps.

[anotherjim]

I don't know if 9v input filtering is shown elsewhere on the schematic. As the 5v regulator output and the 24v powered IC have filtering caps, it's odd if they are omitted on the supply input side.

Pretty much any integrated circuit datasheet suggests ceramic filter caps close to the supply pins (a voltage regulator has 2 supply pins -  in and out). Not fitting them is folly since you don't know when circumstances will change (like a different external PSU) that definitely makes them useful - and it's not like they are expensive.

The series protection diode D2, while a good thing, can cause problems. If you add a series diode, you must include sufficient capacitance in the pedal supply to bypass any AC signal currents since they can't go through the diode without getting rectified and that makes a radio detector! The larger electro caps are good at dealing with power hum and audio while the ceramics handle supersonic/radio frequencies.

There are other ways for electronics to pick up noises that can bypass ordinary capacitor filtering such as ground loops and they are not so straightforward to deal with. We'll hope it isn't this.

[airvian]

I don't know if 9v input filtering is shown elsewhere on the schematic. As the 5v regulator output and the 24v powered IC have filtering caps, it's odd if they are omitted on the supply input side.

Pretty much any integrated circuit datasheet suggests ceramic filter caps close to the supply pins (a voltage regulator has 2 supply pins -  in and out). Not fitting them is folly since you don't know when circumstances will change (like a different external PSU) that definitely makes them useful - and it's not like they are expensive.

The series protection diode D2, while a good thing, can cause problems. If you add a series diode, you must include sufficient capacitance in the pedal supply to bypass any AC signal currents since they can't go through the diode without getting rectified and that makes a radio detector! The larger electro caps are good at dealing with power hum and audio while the ceramics handle supersonic/radio frequencies.

There are other ways for electronics to pick up noises that can bypass ordinary capacitor filtering such as ground loops and they are not so straightforward to deal with. We'll hope it isn't this.

https://drive.google.com/file/d/14GZfHa1M3ThQPYdIIEGSTHft33C3Eh2I/view
A full schematic can be found here for reference. I'd first try adding filtering caps to the IC3. I have enough caps laying around so that wouldn't be a problem. What value would you recommend for the kind of noise I get?

[anotherjim]

The standard bypass cap to deal with high frequency is the 100nF ceramic disc thanks to its low self-inductance. However, multilayer (MLCC) radial or axial types also work.
These are absent from IC1 pins 1 and IC3 pin 8 and the power input after D2. The LT1054 data doesn't mandate a ceramic bypass cap for its power pin but shows at least 2uF (2.2uF likely).

Quickly...
Heterodyne noise is the sum and difference frequencies from mixing 2 signal sources. Let's say one source is 30Khz and the other is 35Khz. Either alone is inaudible - they are ultrasonic. The sum is usually of no consequence - 65Khz is also inaudible. However, the difference is 5Khz which is audible. That's a simple case with single, stable frequencies however switching power supplies can produce varying harmonics as load changes and the audible result can be beeps or sweeps.
It's because the cause of this audible noise is from inaudible high-frequency sources that you simply must fit capacitors that can deal with it whether or not you personally get this problem. If you had a different pedal power supply, you would not have noticed!
It's all very well saying use a better supply, but can anyone guarantee that will always be available? For that matter, the PSU grabbed by the user might be 9v DC and have enough current capability, but it could be a basic transformer/rectifier with no capacitors at all! It could be a fine supply with a pedal with plenty of supply capacitance fitted in it. So I would fit at least 100uF after the protection diode in any pedal.


Here's a well-considered pedal DC input. We can ignore the R15/C10 filter and LED, but the first thing after the protection diode is a big cap and an additional 100nF. This will be fairly immune to either switching supply noise or transformer supply ripple hum.

[airvian]

The standard bypass cap to deal with high frequency is the 100nF ceramic disc thanks to its low self-inductance. However, multilayer (MLCC) radial or axial types also work.
These are absent from IC1 pins 1 and IC3 pin 8 and the power input after D2. The LT1054 data doesn't mandate a ceramic bypass cap for its power pin but shows at least 2uF (2.2uF likely).

Quickly...
Heterodyne noise is the sum and difference frequencies from mixing 2 signal sources. Let's say one source is 30Khz and the other is 35Khz. Either alone is inaudible - they are ultrasonic. The sum is usually of no consequence - 65Khz is also inaudible. However, the difference is 5Khz which is audible. That's a simple case with single, stable frequencies however switching power supplies can produce varying harmonics as load changes and the audible result can be beeps or sweeps.
It's because the cause of this audible noise is from inaudible high-frequency sources that you simply must fit capacitors that can deal with it whether or not you personally get this problem. If you had a different pedal power supply, you would not have noticed!
It's all very well saying use a better supply, but can anyone guarantee that will always be available? For that matter, the PSU grabbed by the user might be 9v DC and have enough current capability, but it could be a basic transformer/rectifier with no capacitors at all! It could be a fine supply with a pedal with plenty of supply capacitance fitted in it. So I would fit at least 100uF after the protection diode in any pedal.


Here's a well-considered pedal DC input. We can ignore the R15/C10 filter and LED, but the first thing after the protection diode is a big cap and an additional 100nF. This will be fairly immune to either switching supply noise or transformer supply ripple hum.

Wow, Thank you so much for the thorough and very helpful reply! Really makes sense now. I'll crack open the pedal asap and look for a neat way to implement the fix