An important subject I want to discuss is noise. This because using effect pedals will have impact on the noise level of your rig and especially when using vintage effects. With the term noise I generally mean the signal noise ratio (SNR); the signal we do want to hear in relation to the signal(s) we don't!
There are several types of noise having different effect and causes. I have roughly classified them as follows:
1. HUM = a constant low frequency humming sound corresponding with the AC line voltage frequency of 50 or 60 Hz.
Main possible causes of hum are:
- not- or bad stabilized power-supply
- (current) overloaded power-supply
- inductor (single coil pickup or wah) picking up an AC magnetic field
- bad ground connection or shielding
- nearby electroluminescent lamps (Neon & TL)
2. HISS = higher frequency constant noise, a sizzling sound. This is a random spectrum of all frequency; called white noise and is comparable to sound of sea waves.
Main possible causes of hiss are:
- bad transistors
- high frequency ripple of switching power supplies
- bad BBD chips (chorus & delay effects)
3 .CRACKLE = irregular medium frequency noise. It sounds like a fire place burning dry wood.
Main possible causes of crackle are:
- bad transistor, especially germanium types have this problem
- bad signal cable
4. Radio Frequency Interference (RFI) = receiving radio audio signals, mostly AM band on your guitar rig.
Main possible causes of RFI are:
- bad signal cable
- guitar pickups
- gain setting too high
5. SQEEL = a resonance of one specific frequency that can increase in volume and or frequency rapidly when not in control.
Main possible causes of Squeel are:
- not wax potted guitar pickups
- high gain setting of your guitar rig
- high treble setting of your guitar rig
6. MICROPHONIC'S = knocking sound when knocked on or moved. Can also result in feedback
Main possible causes of microphonic's are:
- not wax potted pickups in combination with high amp setting
- coil in Wah inductor
- bad guitar cable
- bad vacuum tube(s) in your amp