Building a Transformer/Color Box? School me on transformers

[T-rex]

I have been thinking about building a box with some transformers in it to use for my EH12AY7 and to use as a color box for the mix bus or running individual tracks through at mix down.

While I have been kicking this around, it has been recently mentioned in two threads. In this one by Joel:
http://messageboard.tapeop.com/viewtopi ... ight=valve

And this one by Jim Williams:
http://messageboard.tapeop.com/viewtopi ... ansformers

So I find the idea of building some sort of transformer box intriguing, but I don't know much about transformers. What would this entail? Simply two transformers wired to inputs and outputs in a project box? I am sure I would want a nevish type sound (based on my love of the N72 I have) but what transformer ratio? I am going to start reseraching transformers on the net but any advice or starting points would be awesome.

thanks!

[Nate Dort]

1:1 (600ohm to 600ohm) would probably serve you well in this case.

If you want some color, get something with a steel core. Or check out some frequency response charts for the trannys and find something that's not necessarily ruler-flat. New Cinemag CMOB-2S trannys are about $30 each.

[Jim Williams]

Impedance and turns ratio: Those are the specs you need to consider.
Line level transformers are usually 1/1 ratio with 600 ohms typical impedance. 1/1 ratios are unity gain minus transformer insertion losses. You don't want to use a 10/1 mic input transformer for a line input or output unless you want an extra 20 db gain thrown in.

[valverec]

1:1 (600ohm to 600ohm) would probably serve you well in this case.

If you want some color, get something with a steel core. Or check out some frequency response charts for the trannys and find something that's not necessarily ruler-flat. New Cinemag CMOB-2S trannys are about $30 each.

Sorry, sick minds don't belong in the diy section...or do they.

If you're looking for color there are probably cheaper ways to achieve that than to build a tranny box. You'd be better off finding something with more options than just a tranny since that's not always going to make a very big difference, especially if you're using gear that doesn't have a tranny. Why not build or buy something that has that in it and have the best of both worlds? Want something cheap and still DIY with a tranny? Check out a couple PM1000 modules. Those have great preamps built in, can be used as a line device or mic device, and have a nice transformer on the input and you can add a 1:1 transformer on the output very easily. Plus there's a ton of documentation on how to do that.

[T-rex]

That's a good point and I love the SCA stuff I have built. But if we are talking about two trannys (I avoided typing it like that earlier cause I know how you DIY guys are all sick in the head ), four neutrik connectors and a box it seems like it would only run about $80 or so? Not sure how much a PM1000 channel is but I think it's a bit more and I would need two.

I was really thinking about building one of these just as an output for my EH12ay7, so if I could double that up and drive the sh$t out of it every once in a while, I would be down with that.

[T-rex]

I also downloaded a 30 page paper from the Jensen site on transformers that I am reading right now.

[Spindrift]

It could be cool to add a passive trim pot to the output. That way, you could hit the transformer hard and then pull the level back before going into another device.

[T-rex]

That is a great idea. I was thinking of maybe getting a single step down just to drive it harder as an experiment. But passive trim pot would be interesting. . .

[T-rex]

So here is the pdf for the CMOB-2S.
http://www.cinemag.biz/output/CMOB-2.pdf

It has four wires, two on either side. How would I wire this for simplel input and output? What would be ground or would this be unbalanced? I no I am a total newb on this stuff, please bare with me!

[Smitty]

i have considered doing this from a very conceptual point of view, not being anywhere near knowledgable enough to actually undertake the project.

if you do this, you should wire in a whole bunch of different transformers with switches to select which ones are in/out of the chain.

and then you MUST have this laser-engraved on the box:

[T-rex]

i have considered doing this from a very conceptual point of view, not being anywhere near knowledgable enough to actually undertake the project.

Then you and I are right there together!

[atavacron]

so did ya build it?

[???????]

Instead of two trim pots, I'd get one of those precision ALPS dual-gang pots, and use precision <1% tolerance resistors in the voltage dividers. That way you could turn the output level down on both channels at once and have it track seamlessly and accurately.

[T-rex]

Nope, I never built this. Since then I ditched my EH 12ay7 and bought a germanium pre, so while I would still like to do it - maybe to run my Ghost's two buss through - it is way down the line right now. New project is the mnats 1176. I have the board, but I have been too lazy to order the parts to start stuffing it.

[strdsk]

The tranny box still sounds like a good idea to me...