Help! - Enormous amounts of RF interference on Octave + Distortion build

[SeeJayDee]

OK Guys, this is my first post, yay!  unfortunately it's a problem

So I wanted to build an octave/fuzzstortion pedal for a mate and really liked the sound of "22/7" from runoffgroove... http://www.runoffgroove.com/22-7.html
It's basically a CMOS version of the EHX Big Muff Pi.


I was originally using Gus Smalley's 'simple octave up' as the octave effect but eventually opted for his 'Octave Up Sick Box' (OUSB) minus the 1N4148s and using an RC4558P.


Now, I've breadboarded everything together because I like to do so before finalizing a build (eventually I'll be etching my own pcbs but not as of yet). The problem is that the 22/7 + OUSB combination seems to just...hate me. There is a horrible mains hum [ousb into 22/7] and high-frequency whining [22/7 into ousb] (but for the record the original plan was to have the octave effect preceding the distortion). I thought a buffer between the two might help so I added one (1/2 of a 4558p) but now the amp just buzzes until I play something. If I let the note ring out it eventually just cuts off and starts buzzing again.

I'm completely at my wit's end and need halp, ples, halp!

[rousejeremy]

If it's on a breadboard, expect a ton of noise. The enclosure creates a Faraday cage and minimizes interference.

[R.G.]

1. Short, direct leads.
2. Bypass every chip with 0.01 to 0.1uF ceramic as close to the chip pins as you can get it - under the chip if possible.
3. 100 to 1K resistor in series with the input signal at the jack, and 50pF from AFTER the resistor to the ground lug of the jack.

There are other issues, but this will get you started.

For reference, everything oscillates if it has enough gain.

[SeeJayDee]

Swapped out the 4558p buffer for a TL072, it seems to have fixed the oscillation and squealing. (Buffered between the octave and dist.).
Also biased the buffer's input via 1M resistor connected to the 4.5v supply (d'oh! that should have been obvious).

Now all that remains is the mains hum - which might just be the lack of a metal enclosure. However, my improvised faraday cage (consisting of a grounded sheet of al-foil) is not very effective. I could add a 49-51Hz notch filter as a last resort, but I'm hoping it'll be fixed with a good enclosure.

When you say bypass the chip - what do you mean exactly? Put a capacitor across anywhere where there is a signal in and out of a chip? Why?

The RC low-pass filter at the input jack makes sense - probably need to get an Fc of 20kHz or so.

[armdnrdy]

Bypass cap A.K.A. decoupling cap.
Connect from +V to ground as close to the IC pins as possible.
Sends AC component to ground....acts as a reserve.