Hum and power supply?

[zener]

I have power supply http://www.angelfire.com/weird2/zener/My_Power_Supply.jpg. I made a daisy-chain out of this one. I plug a Little Gem and a Hot Silicon, and hummmmmmmm! :x . I pull the plug and put a battery in the Hot Silicon and the hum is gone.

Any addition/mod on the schem I can make to my power supply (voltage regulating transistor?) to get rid of the hum?

Thanks.

Zener

[smoguzbenjamin]

That's odd. My PSU doesn't hum at all with a daisy chain. :? Try a 100uF cap over the power lines in your pedal(s)...

[zener]

Thanks Ben. I'll try that as soon as possible. It's now less than three hours here before new year. I'm going to crank up my amp and guitar to be as loud as possible to compete with those firecrackers blasting outside. :twisted:

Happy New Year!

Zener

[gez]

Here's some useful stuff:

http://www.muzique.com/lab/hum.htm

http://www.muzique.com/lab/filter.htm

[R.G.]

Hum is one of the banes of the high gain distortion pedal. Any hum, no matter how trivial, is amplified by the full gain of the pedal, while the guitar signal is clipped off by the limiting that makes for distortion.

If you have no hum with a battery, you have sidestepped one source, that being not having an input or output jack properly grounded.

Wall warts are particularly prone to making hum by a couple of different paths. One is by simply not having enough filtering. The power supply you show has large filter caps, but little in the way of series filtering. I'd suggest changing the 1K resistor to 50K and inserting a 100 ohm resistor between the first 1000uF and the rest of the filter caps. That should clean up any ripple hum.

Ripple hum from a full wave rectifier is always twice the power line frequency, so you can tell it from AC power line hum if your ear is good. If you have 50Hz AC power, the ripple hum will be at 100Hz; if you have 60Hz AC, the ripple is at 120Hz. Ripple hum is usually more buzzy in nature than power line hum.

Power line hum comes from three places: radiated power line frequency, grounding induced hum, and power line trash noise.

Radiated power line frequency is usually magnetic in nature. The power line is low frequency, but if you think of the AC power distribution network as an antenna, the antenna is everywhere. Some circuits pick up the power line frequency directly as though it were radio. More often, there is a transformer or other power line magnetic part like a motor or fluorescent light ballast nearby radiating the power line AC. Sometimes these parts will radiate three times the power line frequency, or 150/180Hz if the iron is saturating a bit. You attack radiated power line frequency by moving the equipment away from the emitter or redoing your cabling into a smaller package.

Grounding induced hum comes in two variants: ground loops and incorrect/leaky AC wiring.  The leaky wiring is easiest to understand. If your AC power supply (your wall wart in this case) leaks some of the AC line power into the power supply ground, then you hear hum. This can come from a defective transformer or just the parasitic capacitance inside the transformer itself. You might try another transformer to see if the hum changes if you suspect this.

Ground loops picking up hum is something that I explained in my article on the Spyder power supply at GEO (http://www.geofex.com).
It overlaps with the radiated hum pickup, as your ground wires themselves are picking up a difference in AC voltage or magnetic radiation simply because they make a large receiving antenna loop.

Power line trash noise is usually caused by fluorescent light bulbs or dimmers causing a short spike on the AC power line once or twice per AC line cycle. This causes a very buzzy sounding hum.

"So..." I can hear you say, "... all that's neat, but how do I fix my hum?"

-Try the 100 ohm series resistor between the two 1000uF caps.
- If that doesn't work try removing the ground/shield braid from **only one end** of the cable between the two effects. This breaks the loop of grounds from power supply to first effect to second effect back to power supply, and should get rid of any ground loop hum.
- If that doesn't work, try the whole rig in another physical location, preferably another building to see if you're picking up radiated hum.
- If that doesn't work, try another transformer if you can.
[/list:u]

One of these should substantially reduce the hum you get in the daisy chain.

The Spyder power supply idea was based on getting rid of ground loops by using isolated power supplies instead of breaking the ground on cables.

[zener]

Thanks R.G.

I'll do as what suggested as soon as I get my hands on soldering leads as I ran out of it.

Happy New Year!

Zener