Tips for cutting down on excess noise

[mhartington]

Besides using insulated wiring, what else do you all do to cut down on the hum in your circuits?

[Bad Chizzle]

Filter caps on power input.

[mhartington]

Filter caps on power input.

could you explain a bit more? is this just puttin a capacitor or resistor between the output and switch?

[igerup]

Nope, you put an electrolytic cap on the DC jack. Anything between 47uF and 100uF will do. Rated at 16 volts is preferable. Solder it to the + and - lugs on the DC jack. That's the easiest  place to put it.

[mhartington]

the positive leg of the cap to the positive side of the dc power?

[Mark Hammer]

Many people here are too young to remember, but there was a time, maybe 40 years ago, or a little more, when household appliances were not well-regulated.  If you were listening to the stereo, and the compressor pump on the refrigerator or freezer went on, or if your mother was using the sewing machine or vacuum cleaner somewhere in the house, or if your father was using a power tool in the garage, spikes would be produced on the power line that was shared across the entire house, and you would hear all sorts of objectionable static in the stereo, or experience interference on the television picture.

Since then, most household appliances have better motors, and things like stereos and televisions have well-regulated power supplies, such that even though they are sharing wall current with other things, all those spikes on the power lines produced by intermittent surges and dips as other things demand current are removed or smoothed out.

In a similar fashion, all the semiconductors in each of your pedals shares a single common source, usually a 9v battery or a wallwart power supply.  If that power is not adequately smoothed then it may provide 60 cycle hum to everything it powers, directly.  That hum can be virtually eliminated at the source, by regulating the power supply so that it eliminates the hum it gets from the wall socket, but most effects also include some "insurance", in the form of added capacitance between V+ and ground, to further reduce any leftover hum, or reduce any hum coming from poorly regulated sources.

Moreover, the same way that a motor or power tool in one part of the house would impact on an audio device somewhere else in the house by sending spikes along the power lines, there can also be noise produced by one pedal "infecting" another.  Many folks here have experienced terrible buzzing when two digital effects are sharing the same power supply. It doesn't happen ALL the time, but it happens often enough, even though the two or more pedals behave absolutely dead quiet, when used with the same power supply one at a time.  Ideally, a pedal should be protected from not only receiving hum or clock noise from somewhere else, but also from sending it out to nearby devices sharing the power line.

One way to reduce audible hum IS to reduce the bass by means of series capacitors or other filtering techniques that chop out the low bass.  The old MXR Distortion+ and DOD 250 used a method whereby as the gain was turned up, more of the bass was cut, such that highest gain settings had the least bass, and consequently, reduced risk of feeding objectionable amplified hum to the amplifier.

Alternatively, one can treat the hum like some VERY deep treble, and use lowpass filtering to take it out.  A simple lowpass filter is produced by means of a resistor in series, followed by a capacitor to ground.  The rolloff point is given by Freq = 1 / [2 * pi * R * C], where R is in megohms, and C is in microfarads.  So, a 100 ohm resistor, followed by a 220uf cap to ground, produces a filtering action that rolls off all content above 7.2hz at 6db/octave.  By the time you get to 60hz, that's 3 octaves, such that anything on the power line at 60hz will be 18db lower.  That is why you will often see such "decoupling" as part of the power circuitry on pedals, between the battery/power-jack and the rest of the circuit.

[darron]

you might add also using noiseless biasing and metal film resistors. that's more for his than hum though.

ahm. isolated power supplies, and avoiding ground loops. if two effects like your amp and a pedal share the same earth with two different connection of varied length (a power cable from your amp and a power cable from your pedal) and there is no isolation (a transformer) then you can get the two fighting it out and making hum. having a good solid earth tracks back hum too.

if you have AC in a pedal then run it as close as you can to the chassis, that gets rid of some hum. also twisting AC lines removes some.

the filtering idea is always good. i put aschottky diode in series first too. that was if something else is drawing a lot at least MY pedal will be smooth, not that it matters if the other one isn't.

tired... sorry lol. i look forward to other people's ideas...

[petemoore]

  Regulator, takes AC ripple out of DC.
  Floating voltage supplies, break ground loops.
 

[mhartington]

i got a charge pump in one pedal so its regulated and a Jfet buffer to cut out some noise. Its not perfect but its better than it was before

[Bad Chizzle]

Another thing I learned not long ago the hard way, is (don't ever use crap cords!) Now, this sounds like something that should go without saying, but, I thought I had good cords and didn't. Started just Checking them all for noise and found that some of my cords were very noisy! Just something for you to think about.

[petemoore]

Besides using insulated wiring, what else do you all do to cut down on the hum in your circuits?
  Follow the rules. This can be easy when following proven, verified layouts, power supplies grounding techniques, and applying intuitive understanding of inductance, and what comprises 'input source'.
  More will be known about a new layout, after post-build experiences.