i n t r ö d u c t i o n
The cat sure gets a pile of mail asking just how it is a four pawed little creature like herself can make such wonderful electronical devices without blowing up the shop or killing herself.
It's a good question, I'll tell you, but I'm not too sure 'cause an awful lot of time has passed since the cat and me first took up a soldering iron. Truth be told, though, I can tell you that the journey began with a couple of little things like messing around with a junky preamp, a busted tube, sparks, and my poor old grandpa screaming bloody murder.
The first thing we built that actually worked was something nice and easy; something almost anyone can build and something that's usable in a home studio, too.
A clean, well-lighted vacuum tube preamplifier.
We're guessing it's something most anyone can do. You just gotta follow some simple directions and you're there.
Now the first thing the cat and me agreed on was that digging up the parts for a preamp project shouldn't be a pain in the ass. In a perfect constructor world all the parts better come from one or two places and they should set you back around a hundred bucks or so. Of equal importance, the design of the preamp has to be simple and to the electronic point--a vacuum tube, power cord, transformer, some caps, a couple of resistors, grommets, quarter inch jacks and a few other doo-dads.
Cheap parts, simple design.
Perfect.
Take a look at the parts list. There ain't nothing crazy about it and you can get everything on the list at one or two stores. This is the actual list we used to round up all of our parts for the project and by God it worked the first time we plugged it in. Try and follow our directions this first time out.
And don't get all weird thinking about the parts you're gonna use. We decided on certain parts because we've used them before, because they're cheap, because there's a million of them, and because they sound perfect for what we want to do with this thing.
You can go hi-fi after your preamp works.
Here's an Adobe Acrobat file that illustrates a few wiring and parts things that we did to our Lulusonic. Now we've got a couple of fancy paper-in-oil capacitors in the signal chain, metal film resistors all around, clean wire runs--easy stuff that works.
Lulusonic Modifications PDF document
If you've got a mod that worked for you, let us know. We're collecting ideas and will post'em in a section devoted to reader Lulusonic mods. Stuff like adding input and output transformers, like our friend Byron did or changing the value of C2 to 470nF or 1uF as suggested by Lulu's buddy Jakob that "will make interfacing to standard 10K ohm line inputs that much less problematic".
Tube of choice seems to be the 12AU7, which, low and behold, is the tube called for in the original RCA schematic. Test complete!
And remember, this is a learning project, a simple tube based preamp. It's usable but is not the end all to everything in the world. Build it as such. You want to dirty up a clean signal, this'll work. You want some tube sound, this'll give you some tube sound. It is not, however, a Neve preamp or anything like that. It's a simple preamp. Don't get mad at Lulu or think she's an idiot cause the signal to noise ratio is crap, there's no phantom power, there's only one tube, it's using 12.6 volts on the heaters . . .
For a different take on the subject, check out:
A couple of good, honest, smart and cat friendly electronical thinkers.
Lulusonic 77-F ® parts list
Right mouse click, "Save As" to your computer, then size and print
Lulusonic 77-F ® schematic
Right mouse click, "Save as" to your computer, then size and print