Isolating separate circuits

[tasty_beverage]

I've been working on a fuzz/distortion using a CD4049 (unbuffered). The 4049 doesn't sustain the way I'd like, so I thought I'd throw a Really Cheap Compressor circuit in front of it.

I wired it up an it seems that the two circuits are interacting or that the 4049 is backfeeding into the compressor. This is creating a 'putting'/motorboating sound and really harsh distortion.

Any thoughts?

[aron]

It should be no different than connecting the two pedals in series. It sounds like you have oscillation going on. Try each circuit separately before moving on. Tap right into the input and output of each effect and make sure it's working.

[tasty_beverage]

I agree about the oscillation. Since the compressor uses an LED/LDR, I can visually see that the motorboating is getting into the compressor so there seems to be some kind of feedback loop.

Each circuits works fine and without noise when used separately.

I have tried decoupling each IC by using a 100 ohm resistor from VCC to power pin and a 100uF cap from power pin to ground. No changes that I can tell.

[pinkjimiphoton]

i would build a separate supply for each stage.

use your "master power supply scheme" that you prefer, i usually use a diode, a small resistance in series, a big freekin and a little tiny cap between the rails to supply a relatively clean source.

then use  the clean output of that to two more big caps... say if ya used 100u above, make these say 47u or so... with a resistor between them to decouple them further. take the output for power to each circuit right off its own cap.

its kinda like how a tube amp power supply is decoupled. it does work sometimes.

motorboating in audio circuits, particularly high gain ones, is usually from too much bass getting in and making it unstable. if you're going series,  you may want to play with the cap value at the output of mictester's compressor. you don't need an output cap there if you have an input cap on the overdrive. one should be plenty. you may not need one at all between them. but i'm not sure.

voltages will help figure out the issue, too

too large of a decoupling cap from the rail to the power pin of the ic may cause motorboating, too. in tubes, too big a cap in the power supply, particularly with a tube rectified can make the whole amp unstable. dunno if the same applies here.

[tasty_beverage]

Jimi, after researching all day today, I think this is the answer laid out cut and dry... I will report back after I get a chance to breadboard. Thank you so much.

[pinkjimiphoton]

i hope it works out for ya!!

i remember a few years back i had tried to design a chipamp for my bro Dickie Wagner <if ya don't know dick wagner, google him> using a 386 chip and tricked out with a preamp, tone stack, even a crude fx loop... all built into a "fender champ" lunchbox.

i spent two weeks 24 -7 working on that sucker before he came to visit... and had to abandon most of the stuff i had hoped to build into it. as it turned out, the 386 is a current hawg, and doesn't want to be on the same circuit with other stuff sometimes.

so how i ended up salvaging it was ditching most of the baubles and beads, and isolating each section of the power supply to its own circuit... and that finally let it fire up.

so i hope it works out for ya, please let me know how youmake out, if ya still have issues, well, we'll just have to try something else.

btw... since ya seem new... welcome to aron's stompbox forum, the greatest place on earth with some of the best people who ever lived. peace!

[amz-fx]

I wired it up an it seems that the two circuits are interacting or that the 4049 is backfeeding into the compressor. This is creating a 'putting'/motorboating sound and really harsh distortion.

The ground connections are just as important as the power leads. Each circuit board should have a ground wire going directly back to the power jack where the big filter capacitor is added (as close to the jack as possible). The circuit boards should share as little of the ground path as possible.

Not a guaranteed fix but it is an item to address.

Best regards, Jack