Hiss & Hum

Only a few ideas and experiences on this topic.

• The frequency also lets you conclude where the hum comes from. Let's assume that it is a mains hum. Then it must be determined whether it already was buzzing or started suddenly.
  
  
• If the hum just arose, a power supply capacitor could be leaking or a tube is close to the end. Perhaps there is an electro-mechanical problem, for example a contact is broken, etc ... also solder residues on the sockets of the pre amp.
  
  
• If you have hum at a recently finished homemade amp, the grounding is mostly to blame. Read the relevant literature.
  
  
• It may be due to the location of the transformer wirings, for example, if an unshielded choke or output transformer is too close to the power transformer. Test by tilting about an axis. Also, the transformer can transmit the hum directly to the speakers. Then it's also buzzing even when unplugged.
  
  
• If the hum is irrespective of the equalizer settings, I would say it is the power supply .... maybe add an additional choke. Especially in SE and amps with spring reverb.
  
  
• If you hear a very "hoarse" hum and noise, the heater is not properly symmetric. Also pay attention to the twisting of the heating wires and put them along the chassis.
  
  
• The Champion 600 as has a strong heating hum. It is also volume dependent, at Vol. 9 almost gone and then it becomes stronger again.
  
  
• If an amplifier feedbacks and whistles (at self during test) wildly from the speaker, while no source is present, it could be due to the phase of the feedback. Just replace the connectors of the output transformer at the the anodes.
  
  
• If you hear high frequencies or radio .... a "grid stopper" (grid resistor V1) is your friend.
  
  
• If it sounds a little cloudy with raining, always recurring, could be a "leaking" coupling capacitor.
  
  
• Fits with: If a Poti makes strange noises when activated and an exchange does not change, maybe DC voltage is in the house. A coupling capacitor or a capacitor of the tone control may be broken. So far only SilverMica types struck me as a source of error.
  
  
• When you hear the logon sound of a mobile phone and similar crossfeeds quite strong, the chassis is not completely grounded. If necessary, use and grounded aluminum foil (Tesa).
  
  
• If you use connect shielded cables only, only connect on one side (Start) with the ground, if the ground should not be "transported".
  
  
• Hearing nothing at all, may be due to the input jacks. In open Switchcraft jacks, sometimes the switching function is not working. The signal is always zeroed.