Unbalanced to blanced

[mettula]

Hi all,
sry for asking again, but can anyone tell me how can I convert an unbalanced signal to balanced signal. Do I need a BALUN transformer? or just a centre tapped transformer?? can anyone also suggest a brand of such items???

Thanks very much
matthew

 

[audioguru2]

It depends on the frequency. Audio? Low RF? High RF? UHF? All the TV RF frequencies?

 

[mettula]

audio frequencies 20hz to 20khz

 

[audioguru2]

Good microphones are balanced already. An audio transformer cuts high and low frequencies unless it is expensive and picks up magnetic mains hum unless it has expensive mu-metal shielding.
An old opamp will add noise and cut high frequencies but a newer opamp will convert unbalanced audio to balanced audio .

 

[mettula]

Audioguru,  can you post me a circuit or help me visualize a circuit of the balancing op-amp please.
Is it putting the input through an inverting opamp of 0 gain, and than putting the output to pin 3 of the xlr?

 

[audioguru2]

Two opamps can convert an unbalanced audio signal to balanced. One opamp is non-inverting and the other opamp is inverting. They both have the unbalanced signal as their inputs and both have the same gain.

 

[mettula]

ok thanksa audio guru - but another questions;

1) which you think is of best quality, a balun transformer or an opamp?

2) about the opamp which you think is best? tl 071??

thanks

 

[audioguru2]

1) which you think is of best quality, a balun transformer or an opamp?

I told you already. An expensive transformer will have a good enough audio bandwidth and will have mu-metal magnetic shielding to avoid picking up mains hum. A good opamp doesn't have these probems, is smaller and is less expensive.

2) about the opamp which you think is best? tl 071??

The TL071 is not the best but it has good value for an audio opamp. Many are used in home entertainment electronics but not in studio and broadcasting equipment. A TL072 has two opamps and a TL074 has four opamps.

 

[mettula]

can you suggest than a more professional opamp if you please.....

 

[audioguru2]

The OPA134 single opamp, OPA2134 dual opamps and OPA4134 quad opamps are pretty good. Very low noise, wide bandwidth and distortion rated at only 0,00008%.
They have FET inputs so they don't have bias current.

 

[alvinyow]

Hi there,
I'm new to this forum.
Currently, I trying to built a balance - unbalance and vice versa circuit but run on a normal adapter.
The adapter deliver 12Vdc only. In this case how can I power the opamp into the negative rail since I'm just having +12Vdc. I had tried using a 555 charge pump to produce the negative portion. But the current is too small to power 4 pcs of TL074 opamp, besides others circuitry too.
How could I acheive this?
Maybe another question here is. Is charge pump psu good for the balance - unbalance? Will it distort the signal or producing noise to it?
Thanks for reading.
Regards
Alvin

 

[audioguru2]

Hi Alvin,
Welcome to our forum. ;D
Opamps don't need a negative supply. They just need to have their inputs biased to about half the single supply voltage, which is ground when there is a negative supply. Capacitor-couple the input, output and feedback resistor and any opamp works with a single supply.

View attachment 40307