Pedal Hum After Installing Into the Case

[nguitar12]

I have a pedal hum after installing into the case. I am using a metal ring I/O jack so the pedal case is negative terminal after assembling. Will it be the possible reason to introduce the hum?

[antonis]

If IN - OUT jack grounds create some kind of loop (e.g. grounded via metal case AND via gnd wires)..

If case isn't actually grounded (e.g. jacks on painted surface)..

If you live in a country without mains GND wiring (common Neutral/GND)..

If YOUR place has common ground issues..

[GibsonGM]

If you broke something when you installed the PCB...

If a component is touching the enclosure that should not be, such as a "+" wire creating a short to the case....

Are you powering it from battery (try it if not).   Check the resistance from "+" to "-" at the battery snap with the circuit "on" (jack inserted).   Should start relatively high, should not have a short....

Just a couple of ideas, things that have happened to me.    Another thing to do is 'bump' the PCB with a pencil eraser with circuit on to see if anything changes, which would tell you a component is out of place...

[EBK]

Some important questions:
What kind of pedal?
Did you test it before boxing it up? 
If so,
    did it hum then also?
    does the hum change if you touch a control (pot or switch)?

[GibsonGM]

Exactly. Way too NOT enough information, really...

[nguitar12]

Some important questions:
What kind of pedal?
Did you test it before boxing it up? 
If so,
    did it hum then also?
    does the hum change if you touch a control (pot or switch)?

I just found that the pedal hum even without the case. It is a SHO booster circuit. I ended up building a LM317 power supply circuit and the hum gone. Can someone please suggest a reason for this? Since the same power adapter is used for my other OD pedal without humming.

[Cozybuilder]

Maybe the SHO is just a happy pedal, and found its soul mate in the first power source?

More than likely your other pedal has a low pass filter (LPF) on the power input, and the SHO doesn't. A good LPF is a series resistor (say 47 ohms) followed by a large capacitor (100 micro farad) to ground, forming a low pass with knee at about 34 Hz. This should get rid of most of the hum.

http://www.learningaboutelectronics.com/Articles/Low-pass-filter-calculator.php

[EBK]

Is your other OD pedal op amp based?
Op amps are generally good at suppressing power supply variations to their output.  An individual transistor, like in the SHO, is not good at that. 

[nguitar12]

Is your other OD pedal op amp based?
Op amps are generally good at suppressing power supply variations to their output.  An individual transistor, like in the SHO, is not good at that.

Yes it is a TS type op amp circuit 

[duck_arse]

^ what ebk says, cmrr and stuff like that.