AX84 Firefly
Background
This is the first amp I ever built. I opened it up recently to fix a joint that went bad over time and realized how much progress I made since then regarding soldering, wiring and component placement. Regardless of that, it’s a great little amp and below is the original build report I wrote back then.
Components
There aren’t many good audio-grade components here in Serbia so most parts are ordered from Germany, UK or USA. I purchased good metal film resistors in local store and power transformer is also built here. AX84.com offers many low-wattage amp designs, but I finally decided to go with FireFly, 1.5W hi-gain amp which offers good cranked tone at bedroom level and is not too complicated to build for a newbie. Power transformer was custom made by Trafomatic and output transformer is Hammond 125A. For caps I used mostly Orange Drops for nF range (and one Xicon Poly film in tone stack), Silver Mica for pF range, filter caps are F+T electrolytes and few caps are great Solen Fast poly. One of those Solen caps at 2.2uF is used as treble bleed at L-Pad. Those ECC83 and ECC81 tubes are EI and 12AT7 is N.O.S. General Electric. Hookup wire is 1000V solid core in different colors, a gift from AmpMaker.com (HUGE thanks). As for the speaker, one of few dedicated guitar speakers you can find in Serbia is Celestion Greenback G12M. I got one of these to make a cabinet.
Mods
- added single knob Marshall 18W style tone control for more versatility
- added L-Pad power attenuator since I need really low volume
- added Master volume control
- tried changing output tube with 12AT7 (ECC81) for more sustain and distortion (and a bit less volume) but came back to ECC82
Update (June 2010)
From this perspective, the only mod I would keep is the L-pad. It’s unnecessary to have both that and the Master volume. I found that Tone control is maxed all the time, so it would probably be better off without that too. In the meantime, some good folks started making PCBs for this great little amp which makes it even easier to build.
Pictorial
Click on an image to see more details.
Useful links
AX84.com project page
Paul Marossy’s board layout
Harmony Central AX84.com Firefly reviews
Hi! Looks really good, nice idea with plexi! I really like it… Can you please tell me how can i add master volume like you? Im going to build with tone controll and master vol like you. Can you please send me your schematic? My email adress is J.kohout2006@seznam.cz Tahnks!
Hi! Great project. Very nice build. Can you just tell me where did you get Hammond 125A?
tnx! Got it from tubetown.de
Cheers
Love your project! GREAT idea with the plexi face!! You know what, I used fabric to upholster my Fender Frontman 25R like an old Fender Tweed and it looks awesome.