Balanced line out using a op-amp? (sorry non-tube related)

[PrecisionB]

Hello All,
I am building a bass preamp and wanted to have a balanced output. Instead of using a transformer to switch from hi-z to low-z I was wondering if I could just do it with an op-amp (I have a NE5532 kickin around) First of all, is this possible? Secondly, what is the absolute simplest way to do so? Could anyone post a schematic? Sorry if this comes off as sort of a stupid question, I am somewhat of a beginner. Thanks for the help!

-Patrick

[selloutrr]

I'm not sure an opamp will give you what you are looking for I could totally be wrong! But even on great vintage preamps such as an API 312 card there is still an input and output transformer giving you balanced outs. The opamp works to increase the level from milivolt to volt.
Hense the "amp" in opamp

the simpliest way to do a balanced out is still a transformer "jensen transformers" are sought after in the studio.

You might want to look for an swr or trace Elliot preamp schematic that may help if an opamp is possible.

[PrecisionB]

I think I found something. Im gonna try It out and see what happens. Would it be safe to be running a pre-amp level into this? Or would that cause distortion?

[selloutrr]

probably distort

the opamp is taking the milivolt and making a line sort of level similar to keyboard no true +4 but much higher then a passive guitar so a preamp is still needed to make the full conversion to line level.

if you take the line level your preamp is giving at the output you will be overloading the opamp ( probably ) unless you stepped your preamp back down to milivolt which pretty much removes the need for the preamp.

this schematic would be best used to ... plug your instrument into and then the out into a mixing console or an extenal preamp line level input.

[BTF]

PB:

If your first idea doesn't work, you might want to have a look at some of the PAIA schematics. I remember a preamp they offered that had an op-amp driver in place of a transformer, and I believe the XLR setup could electronically switch phase as well. It might have been called the "Stack in a Box" or something similar. Their website should mention it.

Good Luck, BTF.

[PrecisionB]

selloutrr,
Don't assume that because this is an "op-amp" that it is automatically amplifying. This particular circuit is simply acting as a buffer. This technique is used in many pedals today. If you put in a milivolt your gonna get a milivolt out. It has a unity gain factor. The purpose of this circuit is to change impedance and isolate. Thats it.

The circuit is so simple that I am just going to try it out and see what happens. The only problem I see is the input getting overloaded. In which case I'll try to fix with a voltage divider circuit. The signal for this circuit is coming from a 12ax7. I was just looking for an alternative to purchasing a DI transformer.

[wallybob]

How about using one of these:

http://focus.ti.com/docs/prod/folders/print/drv135.html

[Cliff Schecht]

It's a simple op amp circuit. You use a non-inverting op amp (giving you whatever gain you need, formula is 1+R2/R1) and an inverting unity gain op amp circuit tied to the output of the first op amp. Op amp 1, the non-inverting one, is the "+" side, the inverting unity gain op amp output is the "-" and ground is ground. The PAiA Tube Mic Pre is an interesting variation in that the first stage is inverting as well and has an interesting mixing circuit attached to it. Schematic here: http://paia.com/prodimages/fantusch.gif

[passfan]

This curcuit will convert balanced to un balanced or unbalanced to balanced whichever you like. P5 controls the gain from zero to up around 20db I believe. I use this curcuit as a preamp for a big class A mosfet amp I built that has balanced inputs. I realize it is not an opamp circuit but you could probably copy it to an opamp curcuit.

http://www.passdiy.com/pdf/balzenpre.pdf

[Aurora]

Both the opamp circuit shown and the Balanced Zen should work, and give you a balanced output. You may have to attenuate the input, though, depending on where you tap your signal in the original preamp.
Input to the opamp cct ( and the BalZen) should be 0.7 -1 V to give some headroom - the BalZen maybe as low as 0.1 V, as this circuit have a lot of gain.

[selloutrr]

would this work i just stumbled across it

http://www.fivefish.net/diy/balanced2/default.htm

[Merlinb]

A cheap way of getting the benefits of balanced wiring on the cheap is to use a ground cancelling output, which needs only one opamp (actually it can be even quieter than true balanced wiring!):
[img550]http://www.dself.dsl.pipex.com/ampins/b ... lfig5a.gif[/img]
Full page:
http://www.dself.dsl.pipex.com/ampins/b ... lanced.htm[/img]