Low Noise Pedals?

[kefestvog]

What's the best way to make a low noise pedal?  I have a copy of the Ampeg Scrambler by P. Bryant and I think the thing is quieter when on than in bypass mode.  Quiet, quiet, quiet.

This made me think about ways of making your pedal as quiet as possible.  I heard of amp makers bending all wires in 90 degree angles, I've also heard of single-point grounding (don't really know what it is), clean soldering, etc.

What matters, what doesn't in order to make a quiet pedal, especially when designing a board layout.

[Mark Hammer]

Some pedals have an advantage in terms of quiet simply because of what they do.  For instance, tremoloes and phasers apply very little gain.  In contrast, overdrives and fuzzes, by their nature apply so much gain that any noise coming in with the signal gets multiplied, creating a bigger problem to be solved.  Even worse, compressors apply more gain when all there is to be amplified is input hiss.

Choice of lower-noise components can help, but only in terms of reducing noise generated by the circuit itself.  Megabucks on op-amps and low-noise resistors does nothing to reduce hiss in a fuzz with a gain of 500.

Shielding of certain lines can help, and keeping signals away from where they don't belong also helps.  Though not a criticism of the terrific efforts of all those folks who spend their time developing layouts for the rest of us, you will note that many "vintage" circuits are laid out on much bigger boards than many of us use, and there is good isolation of circuit portions.  What helps to stuff a circuit into a small Hammond box, though, may not necessarily be what keeps the noise demons at bay.  Again, not a criticism, just a concern sitting in the back of my mind.

Personally, I make it a point to take out any bandwidth I don't need.  Many circuits will have tiny feedback caps in op-amp stages to reduce the possibility of ultrasonic oscillations.  That's fine for stuff going on at 70khz, but do I actually NEED all the bandwidth between 10khz and 70khz?  Not likely.  And if a big chunk of it is possible hiss, why keep it?  I just do the calculations and up the feedback cap value to trim the hgh end back to what I need and use only.

Other things include line noise like ticking.  Remember that all the semiconductors in your circuit are sharing the same power supply the same way that all appliances in your home share the same power supply.  If your TV, stereo, or radio do not have adequate decoupling of their power supply circuits from each other and everything else, then when any motor turns on in your home (e.g., fridge, dishwasher, furnace, sewing machine, etc.), their momentary draws on the supply current will be heard as line noise in those audio devices mentioned.  Frequently, "decoupling" can consist of something as easy as a low-value resistor between the battery supply and the V+ pin/input of the semiconductor, and a cap to ground.  Think of it like a "treble control" for the buzz on the supply line.  If you fed +9v to a chip through a 47R resistor with a 10uf cap to ground, you'd have something working like a lowpass filter rolling off at 338hz.  Not perfect, but any high frequency impulse noise on the supply line would be attenuated...hopefully to the point of acceptability, much like dulling a buzz rather than eliminating it

[RandomRedLetters]

Single point grounding is placing all the grounds in a circuit to one point (say the lug of the output jack on an fx pedal) Basically this reduces the chance of grounding loops and shorts that might introduce noise back into the circuit.

As far as bending all the wires 90 degrees, its to reduce the amount of electromagnetic influence each wire has one one another as current passes through it. Fortunately this isn't as big, or even a problem at all in pedals since they aren't using much voltage. It might be a problem in some parts of some amps because of the amount of current they're pulling. Its not something to worry about as a pedal builder.