Firefly 1.5W Tube Amp Build

[SuperSwede]

ooohhhhh! (and everything warren said)

[duhvoodooman***]

Well, after spending a bit more time with this little dynamo, I must admit I'm pretty impressed. It can generate an unbelievable amount of volume considering it's power rating (I suspect that 1.5W is very conservative), and when you crank the boost gain, it has plenty of raunch on tap. And I haven't even really "opened it up" yet, because I haven't had the house to myself since I built it. But I will on Wed. night, and I'll try to record a demo clip then, too.

The only thing I don't particularly like is that it's a little dark sounding, at least at low volumes. The good news is that John Calhoun included an optional "brightness" capacitor spot on his PCB design, so I'm going to get two different value silver-mica caps and wire them to the board via an on-off-on DPDT switch. That'll give me three settings: normal, bright and brighter. That should cover it....

[oldguy]

Vood, that looks fantastic! You do nice work.
Thanks for the pics and updates, you are 'da MAN!!!

[Jimi75]

Why didn't GOD give the talent to assemble small amps and pedals on my own?

This amp looks gergeous and the sound in the clip is killer. I can only look up to people like you - respect!

[duhvoodooman***]

I can only look up to people like you - respect!

Funny, that's how I feel about you when I hear your guitar playing! Thanks for your generous comments, Jimi. Really--the building is easier than the playing!

[tot_Ou_tard]

I waited a bit to make sure that you really have built it now .

Looks beautiful as usual Vood!

Technically speaking, what makes the amp dark. Could you go into a little more detail about how a bright switch works?

You duh_man voodoo!

[duhvoodooman***]

Technically speaking, what makes the amp dark. Could you go into a little more detail about how a bright switch works?

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?

[Jimi75]

Funny, that's how I feel about you when I hear your guitar playing! Thanks for your generous comments, Jimi. Really--the building is easier than the playing!

Thank you :-)

[heatherd66]

Mesa Boogie Express 112 5:25 Tone demo Mic: http://play.kendincos.com/174562/Wrv...-demo-mic.html