Firefly 1.5W Tube Amp Build

[tot_Ou_tard]

As I understand these things, and amp will sound dark if the circuit is laid out such that a large portion of the high frequencies are lost/bled off to ground during the course of amplifying the signal. This tends to be most pronounced at low volumes. Some amps are intrinsically dark sounding, while others are bright, or somewhere in between. Dark sounding amps are often modified in some way to give them more top end, with the addition of the famous "Top Boost" stage to the Vox AC30 being a well-known example. (Interestingly, that circuit was copied directly from an old 50's Gibson amp, right down to an error in the bass pot design!)

However, this can be done in other ways, notably by adding judiciously chosen capacitors to locations in the circuit where they can act as a bypass around points where high frequencies would otherwise be bled off. This works because of the the fact that the impedance of a capacitor varies inversely with frequency, so that at very high frequencies, a capacitor becomes a short circuit, and at very low frequencies, an open circuit. Now, exactly how you decide what capacitance rating to use in what circuit is still a mystery to me, but John Calhoun suggests something in the 200 - 450 picofarad range for the optional brightness cap in the Firefly. So I've ordered several silver mica caps in that capacitance ballpark and will see which I like the sound of best.

Clear as mud?

I think you need to mod the above with a clarity boost

Thanks Vood, that did help some.

[duhvoodooman***]

I think you need to mod the above with a clarity boost....

Got a schematic? I could use one of those!

[duhvoodooman***]

OK, here's a little sample of what the Firefly can do. I came across a posting at the AX84.com Firefly forum that said if you swap a 12AT7 for the 12AU7 power tube, it drops the max. power output but brings on an earlier breakup with a huge bottom end. Since I'm not using close to the max. output of this little monster, that sounded like a pretty good tradeoff to me. So I tried it through my 1x12 cab using my LP Std. and--WHAM--instant mini-Marshall stack sounds! Couldn't think of anything better to ram through it than some vintage Zep. Now, I'll never be confused for Jimmy Page, but playing aside, this sounded pretty good to me. Mind you, this is with NO effects other than a bit of plate reverb from my DigiVerb pedal. All the crunch comes purely from the amp. Here's the link:

http://www.box.net/shared/12u35riuck

[stingx]

SWEET!

I have GOT to build me one of these!

[Tone2TheBone]

SWEET!

I have GOT to build me one of these!

Hell yeah buddy that's what I told him. This is my next amp! Great job Voo! It's inspirational stuff mang!

[duhvoodooman***]

Anybody interested in tackling this DIY amp project, refer to the resource links back in posts #1 and #10 in this thread. John Calhoun's PCB and detailed instructions (with full BOM/source/part # info) really make it quite straightforward! If you have basic electrical knowledge, decent soldering skills and can follow directions, this really isn't that hard to do.... :

[warren0728]

can follow directions

man....i was so close... :

ww

[tot_Ou_tard]

Anybody interested in tackling this DIY amp project, refer to the resource links back in posts #1 and #10 in this thread. John Calhoun's PCB and detailed instructions (with full BOM/source/part # info) really make it quite straightforward! If you have basic electrical knowledge, decent soldering skills and can follow directions, this really isn't that hard to do.... :

Jeez...I gotta look at previous posts & *then* what?!?

Hoo boy! I've got enough trouble trying to replace a speaker .

[F_BSurfer]

oh yea I like that mini marshall!!!!

[tot_Ou_tard]

Sweet is right Vood!!!!

[Katastrophe]

Repost:

Couldn't think of anything better to ram through it than some vintage Zep. Now, I'll never be confused for Jimmy Page, but playing aside, this sounded pretty good to me.

You're right... Page plays sloppier.: The tone you're getting from the amph sounds very warm, even through my little computer speakers. Great stuff, DVM!

Added:

I wish I had your talent with electronics. Put a soldering iron in my hand, and somebody better have a paramedic on standby, with a bed waiting at the nearest burn center.