Firebox - tube power amp emulator

vigilante398

Authorized Vendor
Now that I have my own section I'M GOING TO POST EVERY SINGLE IDEA I HAVE HERE. I have a dedicated section on Talkbass where I can show off things like finished products, but people there don't enjoy geeking out about PCB designs like we do here.

So this is a bit of a misnomer, as it's not actually an emulator, it is a full power amp with a dummy load on the output and a tap to bring down the level so I can feed it into more stuff. A year or so ago someone asked if I could do something like the SWR Interstellar Overdrive, which is a hybrid preamp going into an EL84 push-pull output section but with a dummy load and both line level and D.I. outputs so you get an "emulated" full amplifier at line level.

I wanted to do the same type thing but smaller, so I'm using a 12AU7 self-split output section like the AX84 Firefly and throwing a dummy load on there. It saves space, saves power, saves money, and saves heat over using a traditional power tube. It's not super small as it still needs an output transformer, but the output transformer for a 1/2W amplifier is much smaller than it would be for a 15W or higher, so I should be able to fit it in a 1590X. The end goal is to go tube preamp -> tube power amp -> tube driven IR loader for the most ridiculous all-in-one box anyone could ever ask for. Anyway, just ordered this one, so it will be a couple weeks out, but I'm excited.


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I was just reading up on the Interstellar - what an awesome piece of equipment that is. Are you going to include the Aural Enhancer? I have held on to my Workingman's 15" combo for like 20 years because it sounds so good, and that Aural Enhancer was always a great part of that sound.
 
I was just reading up on the Interstellar - what an awesome piece of equipment that is. Are you going to include the Aural Enhancer? I have held on to my Workingman's 15" combo for like 20 years because it sounds so good, and that Aural Enhancer was always a great part of that sound.
Nope, aural enhancer is an op-amp driven filter that's part of their hybrid preamp, I'm completely scrapping their preamp and using one of my own that's going to be all-tube. I'm not trying to clone the interstellar overdrive, just taking a page from their book on the power section "emulator".
 
a full power amp with a dummy load on the output and a tap to bring down the level

saves power
Interesting.... ;)

Jokes aside. What transformer are you going to use?
Is it the first prototype or have you already had the opportunity to test the circuit (breadboard)?
 
Would the transformer be mounted on the face of the enclosure, or is it small/shallow enough to fit inside the 1590X?
 
Interesting.... ;)

Jokes aside. What transformer are you going to use?
Is it the first prototype or have you already had the opportunity to test the circuit (breadboard)?
Transformer is a Hammond 125A, just like the Firefly. I know I'm still using a lot more power than other preamps, but I'm using a lot less with a self-split 12AU7 than I would have with a 6V6 like I had originally planned :p This will be the first prototype, ordered boards based on faith :p I don't really breadboard anymore, chinese PCBs are too cheap and too fast.

I've built a Firefly before so I know the circuit I used is fine, I just swapped the original preamp for my Space Heater, which is my go-to for testing designs since it's dead simple and hard to mess up. Also just for funsies I have the dummy load on a switch so I can turn off the dummy load and run this thing into a cab.
Would the transformer be mounted on the face of the enclosure, or is it small/shallow enough to fit inside the 1590X?
The transformer is small enough to fit inside the box. I use 1590XX for a lot of stuff, but only the 1590X is deep enough to keep the transformer on the inside, and that's a must for me.
 
I want to see this, Mostly the section of preamp to power amp, I'm not the full purist. I want to try using this or a Black Eye with a SS power section.
 
I want to see this, Mostly the section of preamp to power amp, I'm not the full purist. I want to try using this or a Black Eye with a SS power section.
I'm not a 100% purist in practice, but I have enough customers that are that something like this makes sense. Black Eye into a SS power amp is still delicious. I do a lot more recording on guitar than I do playing out, so I want a rackmount unit that has Black Eye -> power amp sim -> IR loader -> D.I. out. It would be my ultimate recording rig.

Completely clueless as to what this actually was, I did a quick read and I'm intrigued. How many slots will you have?
My digital skills are limited so the final IR loader design is being outsourced to a guy I met at NAMM, trying to remember how many slots he said it will have. 16 maybe? Way more than anyone realistically needs. But that guy is busy and I like things fast, so I just ordered boards for a standalone tube-driven IR loader where I'm doing the digital bits myself, and that will only have 2 slots, the intention being one for guitar and one for bass. That one is in a big order with a bunch of other boards and the last board is almost done, so it's scheduled to ship tomorrow and I should see it by mid-next week, I'll probably start a new thread about that one because it's exciting 😁
 
Nice!

I have an ancient Hafler T-2 rack preamp that uses a single ended interstage trafo which was always kind of a weak point. It sounds pretty decent though in any case. And then I'm sitting on a gifted Mercury Magnetics output trafo made for 6SN7 run in push-pull...one of these days. ;)
 
You guys are scaring me :) I REALLY like the idea of pre > pwr > IR. Although multiple IR slots would be cool I'd think a lot of folks could set on 2 or 4 maybe? In my case I'd probably settle on a 412 closed back into an SM57 and call it a win as long as the sound quality was there.

I also just finished up the Aion preamps that Kevin just put out so I can imagine having a few tube or IC based pre's in a chassis. I've been playing a few places where going straight to front-of-house is the only option so this would be a cool option.
 
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