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help with circuit diagram needed

It makes no sense. There should be nothing between the output and the + input of either amplifier. Take the 5.1 k resistors off pins 1 and 7 and tie them to ground instead. You also want to move the 47 uf caps to the other side of the 120 ohm resistors, as there has to be a DC path between pins 1 and 2 and 6 and 7 of the two amplifiers. Otherwise it should work fine.
 
I agree with moving the 47uF caps.
As for the components between the outputs and the + inputs, it looks like they are there for HF roll-off and gain-setting.

There is a dot on the 'unbalanced signal (+)' input line (just to the right of the arrow block) that looks like it is shorting that line to the GND line. Remove the dot. It may be obvious to some people, but others may interpret it as a connection, in which case you would be correct in thinking that the input is shorted.
 
I would try out the circuit as shown (without the shorted input indicated by the unfortunate dot which shouldn't be there).
The rolloff and gain control 5.1 k an 220 pf form output back to the + input may not be needed, but in the presence of
very much RF, may be useful in suppressing oscillations.

I have always HATED schematics with crossed lines and dots. We were not allowed to draw schematics this way in radio
engineering school, proper "jump over" lines were required on papers we submitted.
It is lazy to just draw straight lines, and it invites mistakes and misinterpretation.

At least this schematic uses the proper symbols for resistors, not just little rectangles (another ugh).

But what KIND of "ground" is represented by the little triangle? Chassis ground? Earth ground?
Some soil in a flower pot? Is it too hard to use one of the approved, standardized symbols?
Is there any reference between this triangle and the +/- supply or does it just float?
How would anyone know? You'll just have to try it out.
 
The unwanted dot at the Unbalanced Signal (+) input seems to be an artifact of the schematic drawing package. Take a look at the 5.1K input resistor on pin 6. It too has a dot at the 90 degree turn where the line connects to Unbalanced Signal Gnd input. There are unnecessary dots all over the diagram. If the vertical line had been drawn over the left by one grid unit, the dot would still be there, but it would not be at the intersection of the lines crossing each other.

Other than that, the circuit looks to me like a garden variety unbalanced-to-balanced signal converter optimized for a high RF environment. I built several of them virtually identical to this one, but I ultimately decided that it was easier, cheaper, and quicker to use a transformer. Plus, I like the sound of transformers.

What is interesting is the designation of Out Pin 2 as Hot and Out Pin 3 as Cold. The signal on Pin 2 is inverted or out of phase from the Unbalanced Signal (+). Moreover, the circuit is really a balanced-to-balanced converter. The inputs are totally balanced. In that application, except for the RFI filtering, you could use two pieces of wire to do the same thing. :)

It would be very easy to debate the need for or value of particular components in the circuit. For example, the 47uF caps are not necessary. The power supply is bipolar, and the op amps are operating at unit gain, so there will not be a DC offset at the outputs. I would argue that the caps are there to protect the circuit from an DC that might appear from the circuit following this one. The 5.1K resistors from the 47uF to ground are to keep the cap from charging, and the 120 ohm resistor is to prevent the 5532 from self-destructing if the circuit is connected to an improper load.

What is the source of the schematic? What is the intended application for this circuit?
 
I love Jensen transformers...great at blocking RF pollution and don't require any power. They sound good to my ears. I always use them for computer interface if not with Livewire over the network. Transformers completely cut the potential ground loop one can still run into as Tom points out in "what is ground".
 
The schematic was drawn incorrectly and it's way more complex than it needs to be.
Reverse the connections to pins 2 and 3. Reverse the connections to pins 5 and 6.
Someone got the + and the - connections wrong. The feedback resistors should go from pin 1 to pin 2 and from pin 7 to pin 6.
Not sure why they added the 220pf capacitors. They're really not necessary.
Since this is a unity gain circuit, you can eliminate the 47uf output capacitors and the 5.1k resistors on the output side of the 47uf capacitors too.
Going from unbalanced (-10) to balanced (+4) requires 14dB of gain. This circuit provides no gain. You can obtain the gain (if necessary) by trimming the value of the 5.1k feedback resistors to a lower value.
 
Wow guys!!! What have I done here :)
Thank you all but after reading all this I came to the decision of using TomT's suggestion:



Parts list: 10 K-ohm resistors (1/4 watt fine) qty. 8
2/ 100 Ohm resistors; one 15 turn 100k pot.
47 uf electrolytics, (3); two .01 mylar or similar caps for power supply rails by-pass; two 27 pf. ceramic; TLO-72 IC.

The TLO 72 is set up as two separate amplifiers. The first stage is pin 3, non-inverting input (+), pin 2 inverting input(-), and pin 1, output. The second stage, pin 5 non-inverting input, pin 6 inverting input, and pin 7 output. The first stage provides the positive going portion of the balanced output, the second stage is fed from the first into the inverting input and provides the negative goi8ng portion of the balanced output. Gain is set with a feedback resistor on the first stage. The 27PF ceramics provide frequency compensation so the amp is not too broad. Requires a bi-polar power supply, +15 vdc to pin 8, -15 vdc to pin 4, use the two .01 mylar caps to bypass the supply rails to ground.

Circuit: Unbalanced input to pin 3 of the IC through a 10K resistor, 10 k from pin 3 to ground. Pin 2 connected to ground through a 10 k, then 47 uf cap. Pin 2 and Pin 1 connected together through the 100k variable resistor. The 27 pf ceramic parallels the 100 k variable between Pin 1 and pin 2.

The output of the first stage from pin 1 goes through a 100 ohm resistor, then a 47 uf cap. (this could be non-polarized, but polarized seems to work fine). This is the (+) output portion of the balanced out. The output side of the cap is connected to ground through a 10 k resistor.

Another 10 k resistor goes from Pin 1 of the first stage to the inverting input (pin 6) of the second stage. The non-inverting input (pin 5, is grounded through a 10 k resistor. The "feedback loop" on this second stage is a 10 k resistor paralleled with another 27 pf ceramic. The output of this second stage, pin 7, goes through a 100 ohm resistor and another 47 uf cap. The output side of this cap is also coupled to ground through another 10 k resistor. This will be the low (-) side of your balanced output.



Seems simplier and effective. What do you think? I'm trying to create the layout with PCBWiz and using a tl074 instead on a tl072. A doubt as ocurred to me but I've pmd Tom already.

And the original circuit comes from here: http://www.fivefish.net/diy/balanced/
 
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