FireFly Tweak

[Doug H]

I've seen a few FireFly builders on here so I thought I'd mention this here as well as at ax84.

This is a simple tweak if you're building it with a Hammond 125 series OT. After getting away from this amp for a week or so, I thought it sounded slightly harsh to my ears after using it again. So I re-wired the OT to give me the maximum impedance available on the primary (22.5K). Then the conjunctive filter was rolling the highs off a hair too much so I reduced the cap from .003u to .0022u. This sounds nice and smooth now, both with the boost channel and the normal channel without/without pedals. This flattens the freq resp a little and firms up the midrange, not as scooped now. I like this sound for this amp, esp. in high gain- it is very smooth and the bass is still tight.

If you think 22.5K sounds ridiculously high- when I plotted a load line for it a couple weeks ago I realized you could pretty much set it as high as you want for this amp (or at least as high as the 125a would let me;-). Might as well set it where you like the sound the best. Lower impedances will work, so no worries if you're using another type of OT. It's just a personal preference thing.

Here's the updated schematic:

http://home.cfl.rr.com/dbhammond/FireFlyBoost_sch.gif

Doug

[Ansil]

cool man, i dig i dig,  i only have one question, what is the actual function of the cap accross the transformer,  the .0022.  i noticed the last time i made one i forgot to do this, and well it didn't blow up so i was just wondering..  i pm you about it sometime ago, but i never heard back so i didn't know if you got it or not.