Need help wiring DI output in tube preamp

[tedmich]

there are two 1/4" outputs on the SIAB, one positive (+) and one negative (-) or inverted. Sending both of these signals down the same line, with a ground (and optionally shielded) is the definition of a balanced line; its an XLR balanced line if its a 3 pin Canon connector or a TRS (tip-ring-sleeve) balanced line if it uses 1/4 stereo connectors. The wiki has a good explanation as to the utility of this arrangement for decreasing noise, and piggy backing phantom power too. While many do like passive transformer designs to create a balanced signal, op amp active designs also do a very good job, albeit with the requirement of single (or better dual, +/-) DC supplies and assorted components.

If you are set on a store bought or DIY passive transformer circuit by all means go for it, but the SIAB implementation is equivalent and has some good characteristics not found in other topologies, IMHO.

[nbtone]

Thank you for the interesting and informative input. I was very confused when I first began to study this problem, but now I seem to have an idea of what to do if I encounter this question in the future. Op-amps are something that I've never experimented much with in preamp circuits, and I've just run across an article that says they aren't good musically: Discrete FET Guitar Preamp
The price of the jenson transformers is a major obstacle, though, so I'm going to look into the op-amp solution anyway, when I get the time.

[tedmich]

we're all ignorant, just (hopefully) in different subjects!

Rod Elliott has some cool circuits for balanced lines, including discrete transistors, I belive. Also a very simple OP amp: Balanced Transmitter and Receiver II
near the bottom...it would cost ~$2

[nbtone]

I ran across this today. Best Bass DI - TalkBass Forums
Lots of info about Bass DIs.