Superheterodyne receiver wissing

[Baranouil]

Hello guys,

I recently assembled the Superheterodyne receiver, but I'm having some issue.
The pedal works, btpass works, when engaged I can enjoy all the different effects the pedal provides but there is always a wissing sound in the background that screw everythings up.
It seems that when the tone knob of my guitar is at 0 the wissing sound is less but it is still here. I honestly don't know from where it comes from. If anyone has ideas please let me know.
Video for the sound: https://streamable.com/7wjz0n
Schematic: https://www.pedalpcb.com/docs/PedalPCB-SuperHeterodyneReceiver.pdf

Thanks!

[idy]

link to build docs/schematic?

[Baranouil]

Done!

[idy]

that is one crazy circuit! 3 stages of invertor distortion, Square wave, pitch multiplier/divider, pitch modulation...scary!

All that aside:
1) you are using a single coil Strat into a high-gain circuit and...
2) the circuit is not in a box. Putting it inside an enclosure (even a temporary, like a cookie tin with grounding to the jacks) would be my first experiment.

[Baranouil]

Yeah indeed the circuit is quite crazy x)

I'm using a mustang.

But I will try to put it in a box!

[anotherjim]

It looks like the designer did a good job of putting plenty of supply filtering capacitors on everything but...
Have they forgotten to terminate the unused inverter inputs? That can cause interference noise. Easy though tedious fix to link the unused inputs to the ground pour. That's IC2 pins 9, 11 & 13 and IC3 pins 5, 11 & 13. Even if that isn't causing the noise, it should still be done as they can take a lot of current if they are allowed to float around.

[Baranouil]

Thanks for that. I am not sure the noise comes from there, since I believe other people built this PCB and don't have it. I will still try to do so if you recommend it.
However, I am not sure to know how to do so. Any advice?

[anotherjim]

I don't know if it needs doing so I posed a question..

Have they forgotten to terminate the unused inverter inputs?

The schematic shows the inputs having no connection. The PCB image apparently shows no connections to those pin pads. The PCB you have may have them connected due to a revision that the document hasn't caught up with.
The "ground pour" is the large area of copper around the IC pins. The ground pour is connected to ground 0v of the power supply.
It is "best practice" to connect unused input pins to some voltage unless they are labelled "NC" on the schematic. In the case of unused devices (you have 6 of them), 0v is preferred although you can use the +supply voltage if that's easier to reach. I would scrape a little of the solder resist coating off the ground pour and solder bits of wire from the pin pads to it. Be sure to leave the unused output pins unconnected as they are.
Noise comes from the unconnected input pins acting as aerials and picking up stray radio-frequency noise and amplifying it to the outputs. Connecting them to something stops that. However, putting it in a screened enclosure stops the radio noise from getting in anyway. So it's perfectly possible to build this and not notice a problem.
However, even in the absence of noise, letting the inputs float can cause the unused inverters to get to a state where they draw excessive supply current, which is why it's "best practice" to connect the unused ones.

[eh la bas ma]

Noise comes from the unconnected input pins acting as aerials and picking up stray radio-frequency noise and amplifying it to the outputs. Connecting them to something stops that. However, putting it in a screened enclosure stops the radio noise from getting in anyway.

Do you mean aluminium enclosures won't stop radio-frequencies, but sheet-metal enclosures would ?

[amptramp]

Both cast aluminum and folded sheet aluminum or steel enclosures will act as shielding, provided you have contact across the edges such as between the surfaces on the casting body and lid or at the edges on the folded sheet metal.  Aluminum can even give some magnetic shielding because a varying magnetic field will induce currents in the aluminum that will greatly reduce the magnetic field inside the enclosure.

Aluminum is generally better at shielding radio frequencies because it is more conductive than steel.

[anotherjim]

Any conductive enclosure ought to screen. See "Faraday cage".

[idy]

The original poster can't see us, but we are (almost) all wearing hats like that. Some are fancier, but basically like that. We should direct new members to our great "Foil Hat Best Practices" thread... Where to ground them, aluminum vs copper (don't mix them!) full face or cranium only, other body parts to shield... a goldmine. Or maybe bauxite.

[eh la bas ma]

I always forgot to wear my aluminium hat, and I never had any issue with my builds...so far. I always ground all my cups of coffee though, because of the unique taste.

I didn't know they are doing full-face type. What would be the pros and cons versus cranium ? Would an antique greek hoplites helmet do the job ?