Firefly low-wattage tube amp - Projects - Audio Artillery

Firefly low-wattage tube amp

  1. Intro
  2. Power section
  3. Internal wiring.
  4. All wired up
  5. Adding an FX loop
  6. Adding a headphone output
  7. Hum reduction

6: Adding a headphone output

A lot of people have put the below "FireZog" line-out circuit in their fireflies. I was more interested in a headphone out and someone said swapping the 150 kOhm for a 100 Ohm would work for driving headphones. I also used a 500k pot instead of a 1M since that's what I had lying around. It does work but has a fizzy sound to it. Haven't figured that out yet.


(click for full size)


 

7: Hum reduction

This little amp hummed like a mother once I had it all put together. Which was odd because it sounded pretty quiet when I was building it. I powered it up and removed the lid and - whoa, not so noisy any more. After poking at the wires with a wooden spoon (and one hand in my pocket) I determined when some of the wires in that rats nest get closer to the output transformer there is a ton of hum. Solution...


(click for full size)

One little cable tie and the hum is completely gone. It's so silent you can't even tell if the amp is on or not.


 
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