"Cicada" - 1W tube amp

[vigilante398]

I posted this here rather than in the Sushi Box subforum because the project isn't going anywhere. I originally planned to make this available as a DIY project, but I'm not as happy with the sound as I wanted to be, so I'm scrapping it and coming up with something different.

This is basically a Firefly from the old AX84 project with minor modifications. Basically I wanted to make a tube amp as cheap and easy to build as possible while still getting a good sounding result. I'm taking a 12VDC input and using an SMPS instead of a power transformer, so that helps a lot with both size and cost. Like everything I build, the design strategy was to PCB mount everything possibel, and if it's not possible then connect it in the easiest way possible.

It uses a single 12AX7 for the preamp and a 12AU7 in self-split push-pull, as well as an additional 12AX7 for a switchable boost. It has a pretty sweet drive sound, especially with the boost active, but as one could reasonably expect has nearly zero clean headroom. I tried it through a 1x6, 1x12, and 2x12, and I like the sound of the 2x12 the best but I want this to be a little setup, so I'm contemplating building a 2x6 cab to see how that sounds. Anyway. This is it.

 

[iamjackslackof]

This is super cool! I think it's great that you're making tube-based effects, and now amps, available to DIYers. I do hope you end up releasing this or something similar eventually!

 

[JamieJ]

I’d way prefer to build this over an amp kit! It’s the massive cost of transformers that puts me off personally. I like that this is PCB based and not turret board. I’d definitely be interested in any further similar projects and I’m sure I’m not alone!

 

[Mentaltossflycoon]

Echoing interest in whatever the cicada morphs into.

 

[vigilante398]

I’d way prefer to build this over an amp kit! It’s the massive cost of transformers that puts me off personally. I like that this is PCB based and not turret board.

Yeah transformer cost is the main reason I don't build a lot more amps. Even the tiny output transformer in this one is $55, which is absurd. The majority of the amp builds I've done have been turret board or eyelet board, and I think they make it easy to make mistakes and difficult to keep things tidy without spending loads of time on it. A well-designed PCB has every advantage you would expect of a turretboard and then some.

Regarding the future of this, my main complaint with Cicada is that there's no clean headroom which makes it a tough sell as a pedal platform. My main goal is to get something relatively inexpensive and easy to build that works well for pedals, so the average builder can put something together to jam with. I'm not planning to do something fancy and high powered that you can gig with, but I'm thinking something in the 5W range would be doable without getting too crazy.

I'm still working on the design to make sure it can still fit in the chassis I want to use, but it's looking pretty good so far. It will need a power transformer since the SMPS can't supply enough current for a real power tube, but so far the chassis, transformers, tubes, and tube sockets come to a total of about $150, with the goal of keeping the entire parts cost for the build (not including cabinet, speaker, etc) around $200. It would be a lot more than a pedal project, but a lot less than most amp projects. Maybe look for that one after NAMM, I'm not sure if I'll have time to get it together before then.

 

[Feral Feline]

Very cool little amp, Nathan.


Hope you achieve your DIY-Amp Goal, would love to build one you've designed.

All I ask is that it's louder than the acoustic sound of the pick hitting the strings.

Having said that, even at 5w the neighbours may complain...

 

[Alan W]

Very cool little amp, Nathan.


Hope you achieve your DIY-Amp Goal, would love to build one you've designed.

All I ask is that it's louder than the acoustic sound of the pick hitting the strings.

Having said that, even at 5w the neighbours may complain...

Speaker efficiency is rated at 1watt input. Many guitar speakers are in the upper 80s db at that, some higher. So 5 watts can get pretty loud. I have a headphone amp that puts out ~1.25 watts, and I’ve plugged 91 db/wattt speakers in and was surprised at how they filled the room.

Great project, and I’ll be in line to buy one!

 

[derevaun]

So cool! Getting away from the power transformer is a victory on its own.

I built the Firefly on the last (I think) PCB revision and it definitely earns its reputation as a one trick pony. It also doesn't boost well into high gain (I don't like how that sounds anyway), probably due to the output tube arrangement. But IMHO it reacts beautifully to switching pickups and mild boosts. It will 90s soapbar indie all day long.

I wonder if some of D-Lab's 6CL6 or 6AQ5 output tube ideas might have some promise. They still seem to get over-the-edge fast. But the high gain side sounds pretty boss, at least in this dude's version:

 

[JPK1]

So cool! Getting away from the power transformer is a victory on its own.

I built the Firefly on the last (I think) PCB revision and it definitely earns its reputation as a one trick pony. It also doesn't boost well into high gain (I don't like how that sounds anyway), probably due to the output tube arrangement. But IMHO it reacts beautifully to switching pickups and mild boosts. It will 90s soapbar indie all day long.

I wonder if some of D-Lab's 6CL6 or 6AQ5 output tube ideas might have some promise. They still seem to get over-the-edge fast. But the high gain side sounds pretty boss, at least in this dude's version:

Nice sounding amp. Of course the dude can shred so it won't sound as good with me playing.

 

[jubal81]

Just spitballing:
Could be interesting to use a 6BM8 tube. It's a triode and 3.5W pentode in one tube.
1. A single-tube, 3.5W single-ended amp. This can be clean, or thought of as a power amp to be used with other tube preamp pedals.
2. Add another 12ax7 for a total of 3 preamp stages into a 3.5W single-ended amp. This still keeps it to 2 total tubes.

 

[jubal81]

Checked AES and they've got an output transformer for $20.

 

[vigilante398]

Checked AES and they've got an output transformer for $20.

Yup, there are reasonable ones to be had in the 5W range, that's part of why I'm aiming there. Best deal I'm seeing on a power tranny is around $50, but still $70 for a good quality set of transformers isn't bad.

 

[andare]

Having said that, even at 5w the neighbours may complain...

30W 1x12 here, my neighbors must be deaf or somewhere else

 

[Feral Feline]

I've still got to swap my Tweed-DLX build from 220v over to 110v. Same with my little vintage Trend 5w — its output transformer went south for the winter and never came back so I upgraded to one that can do both 220 and 110.

So my neighbours are just putting up with Trombone and acoustic upright for the time being.

 

[RetiredUnit1]

expensive? hmmm..... I bet when you count price PER WATT it's cheaper to build a 2203.... Iron cost me about $350 including freight and tax, rolling my own chassis, already have the rest of the components.... insanely loud and heavy? As in heavy metal, yes.

Just sorta finishing off the custom layout, for like the past month. Every time I think I have it done I see something I don't quite like. This view has the transformers in a back layer, in their exact position the holes will need to be drilled at. The actual layout for assembly with be sans anything but assembly, and I'm going to make a top down layout too.

I'm retired, all the time in the world........ (I'm also building a couple 5w champs too, quiet has it's time and place)

 

[derevaun]

I posted this here rather than in the Sushi Box subforum because the project isn't going anywhere. I originally planned to make this available as a DIY project, but I'm not as happy with the sound as I wanted to be, so I'm scrapping it and coming up with something different.

This is basically a Firefly from the old AX84 project with minor modifications. Basically I wanted to make a tube amp as cheap and easy to build as possible while still getting a good sounding result. I'm taking a 12VDC input and using an SMPS instead of a power transformer, so that helps a lot with both size and cost. Like everything I build, the design strategy was to PCB mount everything possibel, and if it's not possible then connect it in the easiest way possible.

It uses a single 12AX7 for the preamp and a 12AU7 in self-split push-pull, as well as an additional 12AX7 for a switchable boost. It has a pretty sweet drive sound, especially with the boost active, but as one could reasonably expect has nearly zero clean headroom. I tried it through a 1x6, 1x12, and 2x12, and I like the sound of the 2x12 the best but I want this to be a little setup, so I'm contemplating building a 2x6 cab to see how that sounds. Anyway. This is it.

View attachment 44128

View attachment 44129

Where in the signal path did you put the tone stack?

 

[swyse]

Super interesting project as always. I have been wanting to do more with tubes, but the transformer cost always was a lot for a single project, it's more fun to do 10 cheaper projects, or thats what I tell myself. I've looked at these transformers in the past https://www.antekinc.com/as-05tc300-50va-300vx2-transformer/ I haven't done enough research so I'm not super sure what ones would have enough juice for the tubes we'd want to use for something like that.

 

[vigilante398]

Where in the signal path did you put the tone stack?

Right before the last gain stage.

 

[kweefthief]

Just spitballing:
Could be interesting to use a 6BM8 tube. It's a triode and 3.5W pentode in one tube.
1. A single-tube, 3.5W single-ended amp. This can be clean, or thought of as a power amp to be used with other tube preamp pedals.
2. Add another 12ax7 for a total of 3 preamp stages into a 3.5W single-ended amp. This still keeps it to 2 total tubes.

This seems interesting! Having a power amp to use with the other sushibox pedals would be cool. You could have something like particle accelerator -> space heater -> (this thingy). It'd be like a little fender champ : D