Custom Pedal noise

[RDK]

Hey guys. I made a pedal. It was kinda noisy though. HOWEVER I did not put it in a box. Just a free hanging circuit board. Does the medal plate in the surround help to eliminate noise?

[Enzo]

Circuits carrying signals and especially circuits that have gain need to be shielded, so yes, the metal box matters to keeping noise low.

[Mark Hammer]

Metal boxes DO provide shielding, as Enzo wisely notes. But there is a long and illustrious history of pedals being produced in plastic boxes that are pleasingly quiet. I own a few, and plastic can work just fine, from a signal quality and durability perspective, as long as you aren't brutal in your treatment of them. I regularly test out circuits without a metal chassis, prior to installation, just to confirm functioning, and to see if I like them as is. Any noise at that point elicits intervention. So, a bare circuit board does not necessarily have to sound like a beehive, and is not instantly transformed into a soothingly silent device once it finds its way to Hammond-land.

Noise in unboxed circuits can come from bad layout, with signal paths that ought not to be near each other ending up so. As a novice builder, there is a strong likelihood that you've made some sort of distortion circuit. Those are high gain, and higher-gain signal runnng to and from pots and switches can easily misbehave of the wires cross over each other. Failure to tend to matters at some key locations can also generate internal noise that will NOT be solved by the shielding of a metal box. There is also shielding on the way from the input jack and on the way to the output jack. That can be very helpful.

It also pays to do your testing in the right environments. Sadly, both my office and my garage workbench have fluorescent lighting, which generates all sorts of hum. Recently, I finally made the switch from CRT to LCD monitor, and that helped considerably in reducing hum on the testpad.

Finally, I don't know what circuit you are working on or what components it might use, but there can be lower and higher noise version of the same general categories of devices. For instance, I have a Behringer pedal that is essentially a clone of the Boss AC-2 acoustic simulator. Unfortunately, Behringer decided to use TL064 quad op-amps to make it, and those chips, while saving on current drain and extending battery life, are hissier than many of the other alternatives, and a pedal that gooses the top end is NOT where you want to use those. If I could get in there and replace the TL064 chips with TL074, I surely would...but it's a packed surface mount board. The point is, that perhaps you can reduce noise by use of more suitable transistors of op-amps.