Firefly 1.5W Tube Amp Build

[duhvoodooman]

Well, on to the next project! This is a cool one. Mentioned HERE back in Sept. by then-new-member Tunghaichuan, I was immediately smitten with the idea of building it. All the info you need is available on John Calhoun's website, where you can also purchase the PCB for the amp build for a very reasonable $19. If you want to hear what this little sucker is capable of, check out THIS CLIP. Sounds like a mini-Marshall stack, no lie!

Between some spare components that Tung was generous enough to send me at no charge, and the rest of the parts order from the sources given in Calhoun's amazingly complete instructions, I've started construction, and finished the PCB fab tonight. Below are some pics, tubes & all. It uses two 12AX7's for the main preamp and a switchable boost stage, and the power tube is a 12AU7!! Now comes the hard part--drilling the chassis and putting all the hardware together. I'll post back here as I make further progress.

 

[Algonquin]

That sound clip is Killer DVM!

Good luck with the rest of the build... Would absolutely love to hear the completed project! :AOK:

Way Cool! :beer:

 

[Robert]

That looks cool! Imagine that thingy on top of a 4x12... what a sight, hehe...

At least you won't need rubber feet for it! :bravo:

 

[Tone2TheBone]

Or wheels. Heard that little sucker today and yeah it rocks heavy. I think I want one.

 

[sunvalleylaw]

What was that clip played through? Wow!

 

[duhvoodooman]

What was that clip played through? Wow!

A closed back 1x12 cabinet with a Celestion G12H30. Sounds bigger, doesn't it? :dude: :rockon:

 

[tot_Ou_tard]

Emminently cool Vood.

Was that your Goldtop straight in?

 

[duhvoodooman]

Was that your Goldtop straight in?

Oh, sorry if I was misleading! No, the clip isn't me (I wish!!), it's a clip posted on the Firefly project page at AX84.com. Doesn't say who the player or the guitar is, though it certainly sounds like an LP or similar humbucker guitar.

 

[tot_Ou_tard]

Oh, sorry if I was misleading! No, the clip isn't me (I wish!!), it's a clip posted on the Firefly project page at AX84.com. Doesn't say who the player or the guitar is, though it certainly sounds like an LP or similar humbucker guitar.

My bad. I do see now that you haven't built the dang thing yet!:thwap:!

That would'a be some trick, playing through a pile of tubes & bits n' bobs!

 

[duhvoodooman]

My bad. I do see now that you haven't built the dang thing yet!:thwap:!

That would'a be some trick, playing through a pile of tubes & bits n' bobs!

Yeah, they're kinda quiet without power and output transformers wired in!

BTW, some more excellent clips can be found at the following link. Scroll way down the page to the "Amps" section of clips, and you'll see the Firefly listed there. There's a nice set of 3 clips that demo the clean, mid-gain and hi-gain sounds. Humbucker guitar, but it doesn't say what the cab was. There's also a clip by Doug Hammond (more on him below). Here's the link:

http://www.mrdwab.com/john/soundclipspage.html​

A bit more "credit where credit is due":

The Firefly is the brainchild of Doug Hammond, a familiar name among DIY amp builders. It's one of several amp projects listed at the AX84.com website, a very cool DIY amp building site run by Chris Hurley, the proprietor of Doberman Music Products. There are some nice bigger DIY tube amp projects there, too, if you're looking to build something with more muscle. What John Calhoun did was to take the project and design a very nice PCB to build it on, and then put together a really outstanding set of instructions, complete with a full bill of materials, sourcing/part # info (this saves hours!), chassis templates, and more. A big tip o' the hat to Doug, Chris & John! :AOK: :bravo: :dude:

 

[sunvalleylaw]

Hmm, what cab would you pick to run with it? Would one of those sale ones from a few months back do a good job?

 

[duhvoodooman]

I expect I'll use it extensively with both the 1x12 I assembled myself and the 2x12 Drive cab I bought during that insane Music123 close-out sale. A 4x12 would probably sound great, but it's getting a bit ridiculous to be playing a 1.5W through a cab that size! Not that it would stop Tone.... :rockon:

 

[Tone2TheBone]

I wanna see what that circuit would like like in one of M29's amp head creations!

ps - you're right Bob nothing stops me moo ah ah ah

 

[abraxas]

Wow!!! :bravo:

That sounds great!!! :AOK:

 

[mrmudcat]

Not to thread hijack but after having god awful (still have) internet problems lately(upgrading system:whatever: ) I got to post fast no time for a big thread. You have given me the bug to do my own SKYDOG project.I think im going with package 2 all the parts just assemble.Im going to do a special cab:smile-us: Vood if I dont hear from ya or vice versa we are still on with book and pedal:beer:

http://www.ceriatone.com/productSubPages/BSPlexi50Bass/BSPlexi50BassKits.htm

 

[duhvoodooman]

WOO WOO WOO!!!! Finished the Firefly build and fired it up Saturday evening--worked the first time!! :dude: The chassis hasn't been painted yet, but it looks pretty cool just the same. Here are some pics, below. Haven't had much chance to play through it yet (out last night at a school function and at church this morning, and now my daughter's asleep on the family room couch!), but the little sucker screams, especially with the boost enabled (insert evil grin/maniacal laughter here). :rockon:

Looking across the front panel from left to right, it's the input jack, boost switch, boost gain, main gain, standby switch, power switch and power indicator light.The power transformer is the larger black one on the right, and the output tranformer is to its left. The tubes (l to r) are boost (12AX7), main preamp (12AX7), and power stage (12AU7).

Will post a clip or two when I have a chance....

 

[warren0728]

:drool: :bravo: :beer: :drool: :bravo: :beer:

 

[sunvalleylaw]

:drool: :bravo: :beer: :drool: :bravo: :beer:

Yeah, all of those, plus pancakes! I kinda like it all industrial and stainless looking. Kinda gives it a 50's tone scientist vibe!

 

[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!!!:bravo:

 

[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

 

[Tone2TheBone]

Holy Moley Voo that's the coolest thing I've ever seen! Let us know how the cap mods do.

 

[aeolian]

Very nicely done. It must be cool to play through an amp you build yourself.

 

[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!