Firebox - tube power amp emulator

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vigilante398

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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.
 
peccary said:
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.
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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".
 
temol said:
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)?
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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.
Bricksnbeatles said:
Would the transformer be mounted on the face of the enclosure, or is it small/shallow enough to fit inside the 1590X?
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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.
 
Deperduci said:
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.
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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.

fig said:
Completely clueless as to what this actually was, I did a quick read and I'm intrigued. How many slots will you have?
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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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