[Born2bwire]

I apologize if this has been addressed before but I could not find a black and white answer to this. If I want to design a balanced in-->balanced out headphone amplifier, what are the design parameters that I need to address. Is it as simple as the following diagram for a single channel:

The signal grounds and power supplies are separate for each channel. For the purpose of argument, just consider the amps to be any general amplifying circuit. What I would like to know is if this configuration is correct and any design considerations that one would need to address.

Also, does anyone know of a simple unbalanced-->balanced conversion circuit. Headwize has one that does the reverse.

 

[skyskraper]

this thread has heaps of cool info on balancing unbalancing and toppling over

 

[Nisbeth]

Quote:

Originally Posted by Born2bwire Also, does anyone know of a simple unbalanced-->balanced conversion circuit. Headwize has one that does the reverse.

Have a look at the DRV134/INA134 ICs from TI

/U.

 

[00940]

Only error in your diagram is that the output has no ground pin. Your drivers on the headphones only have two terminals per side.

 

[Garbz]

Indeed that is true, however in practice provide either a 5th pin anyway to allow the use of an adapter so unbalanced heapdhones can be used, or more importantly connect the ground to the XLR itself. Terminate the shield of the headphone cord to this and you get extra shielding. Now i know this is already elimintating what balanced should keep gone, however since many use starquad, which is shielded, it's a shame to waste the sheild in the cable if it's already there.

Also on the input I sugest you implement a DPST switch to lift pin3 on the XLR. The reason being is that you can flick it to eliminate a possible ground loop since the signal and return are from pins 1 and 2, disconnecting ground will not cause hum, and may infact often eliminate it.

 

[Born2bwire]

Couldn't I just use a SPST to float or connect the XLR input ground, or should I be tying it to something when if I disconnect it from the signal ground?

 

[Garbz]

true true, i just said DPST since it would give you 2 points to solder to. All that's being done is have the ground disconnected. But then again thinking back someone was having trouble with a ground loop created within his interconnect pair which was fixed when he floated just one cable. I'm not sure if having a continuous ground loop from source across cables, and back to source would have any effect though.