Any preamp buildders?

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shoggoth80

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Hey all. First post in the DIY/Homebrew/Modshop...
I have a friend who dabbles pretty heavily in homebrewing his own gear. We were talking last night about building some of our own kit, and modding other stuff to suit our desires.
The topic of modding my Ballari Mp105 came up. I know that people have replaced the opamps in them to get a hotter unit.

We talked about the idea of a 2 tube mic preamp. Are there any schematics out there? Anyone ever attempt this? I think it sounds like a fun idea. Might be a bit complex for a beginning DIYer, but the idea is too neat for me to not at least look into. I know a lot of the components aren't very expensive... 12AX7 tubes run sub $20 most times, and opamps are cheap. The boards would probably cost a bit to get. However, my friend has the soldering set up, and the general know how that we could probably make something functional between the two of us. He's made a number of effects pedals for his guitar, and is currently working on putting together a larger pedal board comprised of a few projects that he has going at the moment.

The hardest part would be creating the chassis I think. Though I could see the phantom power and padding switches being a headache to wrap my head around.

Anyone ever make their own, or modify their pre to suit them better, or to get a hotter signal out?

Also, I was told Mouser is the place to go for components. Is this pretty much the go to place?
 
digikey is my source for parts... a tube pre may be hard to roll your own withoput some specific data... that said check out this site prodigy.com hardcore modders... you'll even be able to source some kits and pcb's...
 
Search for the NewYorkDave "One Bottle" preamp, or one of the Gyraf projects--G7 or G9, I forget the number. Both are well supported at prodigy-pro.

You will probably find you need multiple sources for parts--Digikey and Mouser are each great, but in different ways sometimes. They have a lot of overlap, but each is stronger in particular areas. Granted I have much larger orders than your average DIY-er, so that might not apply to you; it's nice to be able to get all the parts you need from one vendor.

But you won't find hardly any tube parts at either; you need to go to a specialty vendor for that stuff (PartsExpress has a basic range of tube parts, including Hammond output & power transformers, tube sockets, etc.)

Phantom power and pad switches are very simple to wire up. The tough part will be the power supply; for a tube mic preamp you need a plate supply (anywhere from 100V to 300V; 140V is easiest), a heater supply (6.3V or 12.6V), a phantom supply (you can step up the heater supply with a voltage multiplier circuit). If you want to add opamps for output drivers, then you need either a half-rail or negative supply. The simplest way to go is a 120V:120V:12V-0-12V; you use one of the 120V primaries as your plate supply and the +/-12V for everything else you need. That keeps the cost of the trafo to around $20.

You will also need to use an input transformer, or you can use both halves of one of your twin triodes as a differential input. The latter is less common because you usually want a step-up transformer on the input for improved noise performance anyway.

But look at what has already been done at prodigy-pro; it's all there.
 
This is a good way to get a cheap power transformer for the plate of Tube circuit , You know those plugins in the bathroom that are for a electric razor ?? behind it is a 120v/120v power transformer that will give you about 170vDC, qute small and pretty cheap to buy , you would just need a 12v supply for the heaters and any opamps ....

Cheers
 
I definitely gotta check out Prodigy-pro, and the listed models. I also found a schematic for a multi-tube pre. Probably more complex than I can do myself... but that is what tapping into others brains is for. Thanks for the information guys... got some searching to do.
 
Second to prodigy-pro. That is a regular encyclopedia of DIY. Power transformers for preamp circuits aren't all that expensive as the current requirements are lower. You can get a 250v transformer for something like $16 from Allied which is suitable for the NYD 1 bottle. Also, as indicated above a dual primary transformer will work as well. Look for PRR Varimu, and look at the power supply for that, ingenious really, as designed gets you 100v and 12v using a $16 dual primary transformer, but you can get higher voltages with moderate design changes. I'm in the process of getting parts together for both of these.

Input transformer for a mic pre is another story, depending on what design you're using. You can spend anywhere from $20 for an Edcor or up to $200 for a vintage Altec 4722 that audiophiles want for phono preamps. There is a guy who used a 5:1 Altec , which aren't quite as in demand, wired backwards in front of an Aikido circuit. You could try other 1:5, like the aforementioned Edcors.


NYD
One-Bottle Preamp
GroupDIY - One Bottle/One Bottle2

Aikido
Boozhound Laboratories

PRR:
DIY Factory - diy12au7

A great thing about prodigy-pro is the build help threads. I've put together something like a 100 page booklet on the PRR!

Depending on how much you want to roll your own, check out these sites as well. I've not done business with them, and both in Australia, but they have PCB's and kits:


PCB's and kits:
http://www.jlmaudio.com/shop/

PCB's and lots of info:
http://sound.westhost.com/
 
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